// Copyright 2008 The RE2 Authors. All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// A DFA (deterministic finite automaton)-based regular expression search.
//
// The DFA search has two main parts: the construction of the automaton,
// which is represented by a graph of State structures, and the execution
// of the automaton over a given input string.
//
// The basic idea is that the State graph is constructed so that the
// execution can simply start with a state s, and then for each byte c in
// the input string, execute "s = s->next[c]", checking at each point whether
// the current s represents a matching state.
//
// The simple explanation just given does convey the essence of this code,
// but it omits the details of how the State graph gets constructed as well
// as some performance-driven optimizations to the execution of the automaton.
// All these details are explained in the comments for the code following
// the definition of class DFA.
//
// See http://swtch.com/~rsc/regexp/ for a very bare-bones equivalent.
#include "re2/prog.h"
#include "re2/stringpiece.h"
#include "util/atomicops.h"
#include "util/flags.h"
#include "util/sparse_set.h"
#define NO_THREAD_SAFETY_ANALYSIS
DEFINE_bool(re2_dfa_bail_when_slow, true,
"Whether the RE2 DFA should bail out early "
"if the NFA would be faster (for testing).");
namespace re2 {
#if !defined(__linux__) /* only Linux seems to have memrchr */
static void* memrchr(const void* s, int c, size_t n) {
const unsigned char* p = (const unsigned char*)s;
for (p += n; n > 0; n--)
if (*--p == c)
return (void*)p;
return NULL;
}
#endif
// Changing this to true compiles in prints that trace execution of the DFA.
// Generates a lot of output -- only useful for debugging.
static const bool DebugDFA = false;
// A DFA implementation of a regular expression program.
// Since this is entirely a forward declaration mandated by C++,
// some of the comments here are better understood after reading
// the comments in the sections that follow the DFA definition.
class DFA {
public:
DFA(Prog* prog, Prog::MatchKind kind, int64 max_mem);
~DFA();
bool ok() const { return !init_failed_; }
Prog::MatchKind kind() { return kind_; }
// Searches for the regular expression in text, which is considered
// as a subsection of context for the purposes of interpreting flags
// like ^ and $ and \A and \z.
// Returns whether a match was found.
// If a match is found, sets *ep to the end point of the best match in text.
// If "anchored", the match must begin at the start of text.
// If "want_earliest_match", the match that ends first is used, not
// necessarily the best one.
// If "run_forward" is true, the DFA runs from text.begin() to text.end().
// If it is false, the DFA runs from text.end() to text.begin(),
// returning the leftmost end of the match instead of the rightmost one.
// If the DFA cannot complete the search (for example, if it is out of
// memory), it sets *failed and returns false.
bool Search(const StringPiece& text, const StringPiece& context,
bool anchored, bool want_earliest_match, bool run_forward,
bool* failed, const char** ep, vector<int>* matches);
// Builds out all states for the entire DFA. FOR TESTING ONLY
// Returns number of states.
int BuildAllStates();
// Computes min and max for matching strings. Won't return strings
// bigger than maxlen.
bool PossibleMatchRange(string* min, string* max, int maxlen);
// These data structures are logically private, but C++ makes it too
// difficult to mark them as such.
class Workq;
class RWLocker;
class StateSaver;
// A single DFA state. The DFA is represented as a graph of these
// States, linked by the next_ pointers. If in state s and reading
// byte c, the next state should be s->next_[c].
struct State {
inline bool IsMatch() const { return flag_ & kFlagMatch; }
void SaveMatch(vector<int>* v);
int* inst_; // Instruction pointers in the state.
int ninst_; // # of inst_ pointers.
uint flag_; // Empty string bitfield flags in effect on the way
// into this state, along with kFlagMatch if this
// is a matching state.
State** next_; // Outgoing arrows from State,
// one per input byte class
};
enum {
kByteEndText = 256, // imaginary byte at end of text
kFlagEmptyMask = 0xFFF, // State.flag_: bits holding kEmptyXXX flags
kFlagMatch = 0x1000, // State.flag_: this is a matching state
kFlagLastWord = 0x2000, // State.flag_: last byte was a word char
kFlagNeedShift = 16, // needed kEmpty bits are or'ed in shifted left
};
#ifndef STL_MSVC
// STL function structures for use with unordered_set.
struct StateEqual {
bool operator()(const State* a, const State* b) const {
if (a == b)
return true;
if (a == NULL || b == NULL)
return false;
if (a->ninst_ != b->ninst_)
return false;
if (a->flag_ != b->flag_)
return false;
for (int i = 0; i < a->ninst_; i++)
if (a->inst_[i] != b->inst_[i])
return false;
return true; // they're equal
}
};
#endif // STL_MSVC
struct StateHash {
size_t operator()(const State* a) const {
if (a == NULL)
return 0;
const char* s = reinterpret_cast<const char*>(a->inst_);
int len = a->ninst_ * sizeof a->inst_[0];
if (sizeof(size_t) == sizeof(uint32))
return Hash32StringWithSeed(s, len, a->flag_);
else
return Hash64StringWithSeed(s, len, a->flag_);
}
#ifdef STL_MSVC
// Less than operator.
bool operator()(const State* a, const State* b) const {
if (a == b)
return false;
if (a == NULL || b == NULL)
return a == NULL;
if (a->ninst_ != b->ninst_)
return a->ninst_ < b->ninst_;
if (a->flag_ != b->flag_)
return a->flag_ < b->flag_;
for (int i = 0; i < a->ninst_; ++i)
if (a->inst_[i] != b->inst_[i])
return a->inst_[i] < b->inst_[i];
return false; // they're equal
}
// The two public members are required by msvc. 4 and 8 are default values.
// Reference: http://msdn.microsoft.com/en-us/library/1s1byw77.aspx
static const size_t bucket_size = 4;
static const size_t min_buckets = 8;
#endif // STL_MSVC
};
#ifdef STL_MSVC
typedef unordered_set<State*, StateHash> StateSet;
#else // !STL_MSVC
typedef unordered_set<State*, StateHash, StateEqual> StateSet;
#endif // STL_MSVC
private:
// Special "firstbyte" values for a state. (Values >= 0 denote actual bytes.)
enum {
kFbUnknown = -1, // No analysis has been performed.
kFbMany = -2, // Many bytes will lead out of this state.
kFbNone = -3, // No bytes lead out of this state.
};
enum {
// Indices into start_ for unanchored searches.
// Add kStartAnchored for anchored searches.
kStartBeginText = 0, // text at beginning of context
kStartBeginLine = 2, // text at beginning of line
kStartAfterWordChar = 4, // text follows a word character
kStartAfterNonWordChar = 6, // text follows non-word character
kMaxStart = 8,
kStartAnchored = 1,
};
// Resets the DFA State cache, flushing all saved State* information.
// Releases and reacquires cache_mutex_ via cache_lock, so any
// State* existing before the call are not valid after the call.
// Use a StateSaver to preserve important states across the call.
// cache_mutex_.r <= L < mutex_
// After: cache_mutex_.w <= L < mutex_
void ResetCache(RWLocker* cache_lock);
// Looks up and returns the State corresponding to a Workq.
// L >= mutex_
State* WorkqToCachedState(Workq* q, uint flag);
// Looks up and returns a State matching the inst, ninst, and flag.
// L >= mutex_
State* CachedState(int* inst, int ninst, uint flag);
// Clear the cache entirely.
// Must hold cache_mutex_.w or be in destructor.
void ClearCache();
// Converts a State into a Workq: the opposite of WorkqToCachedState.
// L >= mutex_
static void StateToWorkq(State* s, Workq* q);
// Runs a State on a given byte, returning the next state.
State* RunStateOnByteUnlocked(State*, int); // cache_mutex_.r <= L < mutex_
State* RunStateOnByte(State*, int); // L >= mutex_
// Runs a Workq on a given byte followed by a set of empty-string flags,
// producing a new Workq in nq. If a match instruction is encountered,
// sets *ismatch to true.
// L >= mutex_
void RunWorkqOnByte(Workq* q, Workq* nq,
int c, uint flag, bool* ismatch,
Prog::MatchKind kind,
int new_byte_loop);
// Runs a Workq on a set of empty-string flags, producing a new Workq in nq.
// L >= mutex_
void RunWorkqOnEmptyString(Workq* q, Workq* nq, uint flag);
// Adds the instruction id to the Workq, following empty arrows
// according to flag.
// L >= mutex_
void AddToQueue(Workq* q, int id, uint flag);
// For debugging, returns a text representation of State.
static string DumpState(State* state);
// For debugging, returns a text representation of a Workq.
static string DumpWorkq(Workq* q);
// Search parameters
struct SearchParams {
SearchParams(const StringPiece& text, const StringPiece& context,
RWLocker* cache_lock)
: text(text), context(context),
anchored(false),
want_earliest_match(false),
run_forward(false),
start(NULL),
firstbyte(kFbUnknown),
cache_lock(cache_lock),
failed(false),
ep(NULL),
matches(NULL) { }
StringPiece text;
StringPiece context;
bool anchored;
bool want_earliest_match;
bool run_forward;
State* start;
int firstbyte;
RWLocker *cache_lock;
bool failed; // "out" parameter: whether search gave up
const char* ep; // "out" parameter: end pointer for match
vector<int>* matches;
private:
DISALLOW_EVIL_CONSTRUCTORS(SearchParams);
};
// Before each search, the parameters to Search are analyzed by
// AnalyzeSearch to determine the state in which to start and the
// "firstbyte" for that state, if any.
struct StartInfo {
StartInfo() : start(NULL), firstbyte(kFbUnknown) { }
State* start;
volatile int firstbyte;
};
// Fills in params->start and params->firstbyte using
// the other search parameters. Returns true on success,
// false on failure.
// cache_mutex_.r <= L < mutex_
bool AnalyzeSearch(SearchParams* params);
bool AnalyzeSearchHelper(SearchParams* params, StartInfo* info, uint flags);
// The generic search loop, inlined to create specialized versions.
// cache_mutex_.r <= L < mutex_
// Might unlock and relock cache_mutex_ via params->cache_lock.
inline bool InlinedSearchLoop(SearchParams* params,
bool have_firstbyte,
bool want_earliest_match,
bool run_forward);
// The specialized versions of InlinedSearchLoop. The three letters
// at the ends of the name denote the true/false values used as the
// last three parameters of InlinedSearchLoop.
// cache_mutex_.r <= L < mutex_
// Might unlock and relock cache_mutex_ via params->cache_lock.
bool SearchFFF(SearchParams* params);
bool SearchFFT(SearchParams* params);
bool SearchFTF(SearchParams* params);
bool SearchFTT(SearchParams* params);
bool SearchTFF(SearchParams* params);
bool SearchTFT(SearchParams* params);
bool SearchTTF(SearchParams* params);
bool SearchTTT(SearchParams* params);
// The main search loop: calls an appropriate specialized version of
// InlinedSearchLoop.
// cache_mutex_.r <= L < mutex_
// Might unlock and relock cache_mutex_ via params->cache_lock.
bool FastSearchLoop(SearchParams* params);
// For debugging, a slow search loop that calls InlinedSearchLoop
// directly -- because the booleans passed are not constants, the
// loop is not specialized like the SearchFFF etc. versions, so it
// runs much more slowly. Useful only for debugging.
// cache_mutex_.r <= L < mutex_
// Might unlock and relock cache_mutex_ via params->cache_lock.
bool SlowSearchLoop(SearchParams* params);
// Looks up bytes in bytemap_ but handles case c == kByteEndText too.
int ByteMap(int c) {
if (c == kByteEndText)
return prog_->bytemap_range();
return prog_->bytemap()[c];
}
// Constant after initialization.
Prog* prog_; // The regular expression program to run.
Prog::MatchKind kind_; // The kind of DFA.
int start_unanchored_; // start of unanchored program
bool init_failed_; // initialization failed (out of memory)
Mutex mutex_; // mutex_ >= cache_mutex_.r
// Scratch areas, protected by mutex_.
Workq* q0_; // Two pre-allocated work queues.
Workq* q1_;
int* astack_; // Pre-allocated stack for AddToQueue
int nastack_;
// State* cache. Many threads use and add to the cache simultaneously,
// holding cache_mutex_ for reading and mutex_ (above) when adding.
// If the cache fills and needs to be discarded, the discarding is done
// while holding cache_mutex_ for writing, to avoid interrupting other
// readers. Any State* pointers are only valid while cache_mutex_
// is held.
Mutex cache_mutex_;
int64 mem_budget_; // Total memory budget for all States.
int64 state_budget_; // Amount of memory remaining for new States.
StateSet state_cache_; // All States computed so far.
StartInfo start_[kMaxStart];
bool cache_warned_; // have printed to LOG(INFO) about the cache
};
// Shorthand for casting to uint8*.
static inline const uint8* BytePtr(const void* v) {
return reinterpret_cast<const uint8*>(v);
}
// Work queues
// Marks separate thread groups of different priority
// in the work queue when in leftmost-longest matching mode.
#define Mark (-1)
// Internally, the DFA uses a sparse array of
// program instruction pointers as a work queue.
// In leftmost longest mode, marks separate sections
// of workq that started executing at different
// locations in the string (earlier locations first).
class DFA::Workq : public SparseSet {
public:
// Constructor: n is number of normal slots, maxmark number of mark slots.
Workq(int n, int maxmark) :
SparseSet(n+maxmark),
n_(n),
maxmark_(maxmark),
nextmark_(n),
last_was_mark_(true) {
}
bool is_mark(int i) { return i >= n_; }
int maxmark() { return maxmark_; }
void clear() {
SparseSet::clear();
nextmark_ = n_;
}
void mark() {
if (last_was_mark_)
return;
last_was_mark_ = false;
SparseSet::insert_new(nextmark_++);
}
int size() {
return n_ + maxmark_;
}
void insert(int id) {
if (contains(id))
return;
insert_new(id);
}
void insert_new(int id) {
last_was_mark_ = false;
SparseSet::insert_new(id);
}
private:
int n_; // size excluding marks
int maxmark_; // maximum number of marks
int nextmark_; // id of next mark
bool last_was_mark_; // last inserted was mark
DISALLOW_EVIL_CONSTRUCTORS(Workq);
};
DFA::DFA(Prog* prog, Prog::MatchKind kind, int64 max_mem)
: prog_(prog),
kind_(kind),
init_failed_(false),
q0_(NULL),
q1_(NULL),
astack_(NULL),
mem_budget_(max_mem),
cache_warned_(false) {
if (DebugDFA)
fprintf(stderr, "\nkind %d\n%s\n", (int)kind_, prog_->DumpUnanchored().c_str());
int nmark = 0;
start_unanchored_ = 0;
if (kind_ == Prog::kLongestMatch) {
nmark = prog->size();
start_unanchored_ = prog->start_unanchored();
}
nastack_ = 2 * prog->size() + nmark;
// Account for space needed for DFA, q0, q1, astack.
mem_budget_ -= sizeof(DFA);
mem_budget_ -= (prog_->size() + nmark) *
(sizeof(int)+sizeof(int)) * 2; // q0, q1
mem_budget_ -= nastack_ * sizeof(int); // astack
if (mem_budget_ < 0) {
LOG(INFO) << StringPrintf("DFA out of memory: prog size %lld mem %lld",
prog_->size(), max_mem);
init_failed_ = true;
return;
}
state_budget_ = mem_budget_;
// Make sure there is a reasonable amount of working room left.
// At minimum, the search requires room for two states in order
// to limp along, restarting frequently. We'll get better performance
// if there is room for a larger number of states, say 20.
int64 one_state = sizeof(State) + (prog_->size()+nmark)*sizeof(int) +
(prog_->bytemap_range()+1)*sizeof(State*);
if (state_budget_ < 20*one_state) {
LOG(INFO) << StringPrintf("DFA out of memory: prog size %lld mem %lld",
prog_->size(), max_mem);
init_failed_ = true;
return;
}
q0_ = new Workq(prog->size(), nmark);
q1_ = new Workq(prog->size(), nmark);
astack_ = new int[nastack_];
}
DFA::~DFA() {
delete q0_;
delete q1_;
delete[] astack_;
ClearCache();
}
// In the DFA state graph, s->next[c] == NULL means that the
// state has not yet been computed and needs to be. We need
// a different special value to signal that s->next[c] is a
// state that can never lead to a match (and thus the search
// can be called off). Hence DeadState.
#define DeadState reinterpret_cast<State*>(1)
// Signals that the rest of the string matches no matter what it is.
#define FullMatchState reinterpret_cast<State*>(2)
#define SpecialStateMax FullMatchState
// Debugging printouts
// For debugging, returns a string representation of the work queue.
string DFA::DumpWorkq(Workq* q) {
string s;
const char* sep = "";
for (DFA::Workq::iterator it = q->begin(); it != q->end(); ++it) {
if (q->is_mark(*it)) {
StringAppendF(&s, "|");
sep = "";
} else {
StringAppendF(&s, "%s%d", sep, *it);
sep = ",";
}
}
return s;
}
// For debugging, returns a string representation of the state.
string DFA::DumpState(State* state) {
if (state == NULL)
return "_";
if (state == DeadState)
return "X";
if (state == FullMatchState)
return "*";
string s;
const char* sep = "";
StringAppendF(&s, "(%p)", state);
for (int i = 0; i < state->ninst_; i++) {
if (state->inst_[i] == Mark) {
StringAppendF(&s, "|");
sep = "";
} else {
StringAppendF(&s, "%s%d", sep, state->inst_[i]);
sep = ",";
}
}
StringAppendF(&s, " flag=%#x", state->flag_);
return s;
}
//////////////////////////////////////////////////////////////////////
//
// DFA state graph construction.
//
// The DFA state graph is a heavily-linked collection of State* structures.
// The state_cache_ is a set of all the State structures ever allocated,
// so that if the same state is reached by two different paths,
// the same State structure can be used. This reduces allocation
// requirements and also avoids duplication of effort across the two
// identical states.
//
// A State is defined by an ordered list of instruction ids and a flag word.
//
// The choice of an ordered list of instructions differs from a typical
// textbook DFA implementation, which would use an unordered set.
// Textbook descriptions, however, only care about whether
// the DFA matches, not where it matches in the text. To decide where the
// DFA matches, we need to mimic the behavior of the dominant backtracking
// implementations like PCRE, which try one possible regular expression
// execution, then another, then another, stopping when one of them succeeds.
// The DFA execution tries these many executions in parallel, representing
// each by an instruction id. These pointers are ordered in the State.inst_
// list in the same order that the executions would happen in a backtracking
// search: if a match is found during execution of inst_[2], inst_[i] for i>=3
// can be discarded.
//
// Textbooks also typically do not consider context-aware empty string operators
// like ^ or $. These are handled by the flag word, which specifies the set
// of empty-string operators that should be matched when executing at the
// current text position. These flag bits are defined in prog.h.
// The flag word also contains two DFA-specific bits: kFlagMatch if the state
// is a matching state (one that reached a kInstMatch in the program)
// and kFlagLastWord if the last processed byte was a word character, for the
// implementation of \B and \b.
//
// The flag word also contains, shifted up 16 bits, the bits looked for by
// any kInstEmptyWidth instructions in the state. These provide a useful
// summary indicating when new flags might be useful.
//
// The permanent representation of a State's instruction ids is just an array,
// but while a state is being analyzed, these instruction ids are represented
// as a Workq, which is an array that allows iteration in insertion order.
// NOTE(rsc): The choice of State construction determines whether the DFA
// mimics backtracking implementations (so-called leftmost first matching) or
// traditional DFA implementations (so-called leftmost longest matching as
// prescribed by POSIX). This implementation chooses to mimic the
// backtracking implementations, because we want to replace PCRE. To get
// POSIX behavior, the states would need to be considered not as a simple
// ordered list of instruction ids, but as a list of unordered sets of instruction
// ids. A match by a state in one set would inhibit the running of sets
// farther down the list but not other instruction ids in the same set. Each
// set would correspond to matches beginning at a given point in the string.
// This is implemented by separating different sets with Mark pointers.
// Looks in the State cache for a State matching q, flag.
// If one is found, returns it. If one is not found, allocates one,
// inserts it in the cache, and returns it.
DFA::State* DFA::WorkqToCachedState(Workq* q, uint flag) {
if (DEBUG_MODE)
mutex_.AssertHeld();
// Construct array of instruction ids for the new state.
// Only ByteRange, EmptyWidth, and Match instructions are useful to keep:
// those are the only operators with any effect in
// RunWorkqOnEmptyString or RunWorkqOnByte.
int* inst = new int[q->size()];
int n = 0;
uint needflags = 0; // flags needed by kInstEmptyWidth instructions
bool sawmatch = false; // whether queue contains guaranteed kInstMatch
bool sawmark = false; // whether queue contains a Mark
if (DebugDFA)
fprintf(stderr, "WorkqToCachedState %s [%#x]", DumpWorkq(q).c_str(), flag);
for (Workq::iterator it = q->begin(); it != q->end(); ++it) {
int id = *it;
if (sawmatch && (kind_ == Prog::kFirstMatch || q->is_mark(id)))
break;
if (q->is_mark(id)) {
if (n > 0 && inst[n-1] != Mark) {
sawmark = true;
inst[n++] = Mark;
}
continue;
}
Prog::Inst* ip = prog_->inst(id);
switch (ip->opcode()) {
case kInstAltMatch:
// This state will continue to a match no matter what
// the rest of the input is. If it is the highest priority match
// being considered, return the special FullMatchState
// to indicate that it's all matches from here out.
if (kind_ != Prog::kManyMatch &&
(kind_ != Prog::kFirstMatch ||
(it == q->begin() && ip->greedy(prog_))) &&
(kind_ != Prog::kLongestMatch || !sawmark) &&
(flag & kFlagMatch)) {
delete[] inst;
if (DebugDFA)
fprintf(stderr, " -> FullMatchState\n");
return FullMatchState;
}
// Fall through.
case kInstByteRange: // These are useful.
case kInstEmptyWidth:
case kInstMatch:
case kInstAlt: // Not useful, but necessary [*]
inst[n++] = *it;
if (ip->opcode() == kInstEmptyWidth)
needflags |= ip->empty();
if (ip->opcode() == kInstMatch && !prog_->anchor_end())
sawmatch = true;
break;
default: // The rest are not.
break;
}
// [*] kInstAlt would seem useless to record in a state, since
// we've already followed both its arrows and saved all the
// interesting states we can reach from there. The problem
// is that one of the empty-width instructions might lead
// back to the same kInstAlt (if an empty-width operator is starred),
// producing a different evaluation order depending on whether
// we keep the kInstAlt to begin with. Sigh.
// A specific case that this affects is /(^|a)+/ matching "a".
// If we don't save the kInstAlt, we will match the whole "a" (0,1)
// but in fact the correct leftmost-first match is the leading "" (0,0).
}
DCHECK_LE(n, q->size());
if (n > 0 && inst[n-1] == Mark)
n--;
// If there are no empty-width instructions waiting to execute,
// then the extra flag bits will not be used, so there is no
// point in saving them. (Discarding them reduces the number
// of distinct states.)
if (needflags == 0)
flag &= kFlagMatch;
// NOTE(rsc): The code above cannot do flag &= needflags,
// because if the right flags were present to pass the current
// kInstEmptyWidth instructions, new kInstEmptyWidth instructions
// might be reached that in turn need different flags.
// The only sure thing is that if there are no kInstEmptyWidth
// instructions at all, no flags will be needed.
// We could do the extra work to figure out the full set of
// possibly needed flags by exploring past the kInstEmptyWidth
// instructions, but the check above -- are any flags needed
// at all? -- handles the most common case. More fine-grained
// analysis can only be justified by measurements showing that
// too many redundant states are being allocated.
// If there are no Insts in the list, it's a dead state,
// which is useful to signal with a special pointer so that
// the execution loop can stop early. This is only okay
// if the state is *not* a matching state.
if (n == 0 && flag == 0) {
delete[] inst;
if (DebugDFA)
fprintf(stderr, " -> DeadState\n");
return DeadState;
}
// If we're in longest match mode, the state is a sequence of
// unordered state sets separated by Marks. Sort each set
// to canonicalize, to reduce the number of distinct sets stored.
if (kind_ == Prog::kLongestMatch) {
int* ip = inst;
int* ep = ip + n;
while (ip < ep) {
int* markp = ip;
while (markp < ep && *markp != Mark)
markp++;
sort(ip, markp);
if (markp < ep)
markp++;
ip = markp;
}
}
// Save the needed empty-width flags in the top bits for use later.
flag |= needflags << kFlagNeedShift;
State* state = CachedState(inst, n, flag);
delete[] inst;
return state;
}
// Looks in the State cache for a State matching inst, ninst, flag.
// If one is found, returns it. If one is not found, allocates one,
// inserts it in the cache, and returns it.
DFA::State* DFA::CachedState(int* inst, int ninst, uint flag) {
if (DEBUG_MODE)
mutex_.AssertHeld();
// Look in the cache for a pre-existing state.
State state = { inst, ninst, flag, NULL };
StateSet::iterator it = state_cache_.find(&state);
if (it != state_cache_.end()) {
if (DebugDFA)
fprintf(stderr, " -cached-> %s\n", DumpState(*it).c_str());
return *it;
}
// Must have enough memory for new state.
// In addition to what we're going to allocate,
// the state cache hash table seems to incur about 32 bytes per
// State*, empirically.
const int kStateCacheOverhead = 32;
int nnext = prog_->bytemap_range() + 1; // + 1 for kByteEndText slot
int mem = sizeof(State) + nnext*sizeof(State*) + ninst*sizeof(int);
if (mem_budget_ < mem + kStateCacheOverhead) {
mem_budget_ = -1;
return NULL;
}
mem_budget_ -= mem + kStateCacheOverhead;
// Allocate new state, along with room for next and inst.
char* space = new char[mem];
State* s = reinterpret_cast<State*>(space);
s->next_ = reinterpret_cast<State**>(s + 1);
s->inst_ = reinterpret_cast<int*>(s->next_ + nnext);
memset(s->next_, 0, nnext*sizeof s->next_[0]);
memmove(s->inst_, inst, ninst*sizeof s->inst_[0]);
s->ninst_ = ninst;
s->flag_ = flag;
if (DebugDFA)
fprintf(stderr, " -> %s\n", DumpState(s).c_str());
// Put state in cache and return it.
state_cache_.insert(s);
return s;
}
// Clear the cache. Must hold cache_mutex_.w or be in destructor.
void DFA::ClearCache() {
// In case state_cache_ doesn't support deleting entries
// during iteration, copy into a vector and then delete.
vector<State*> v;
v.reserve(state_cache_.size());
for (StateSet::iterator it = state_cache_.begin();
it != state_cache_.end(); ++it)
v.push_back(*it);
state_cache_.clear();
for (int i = 0; i < v.size(); i++)
delete[] reinterpret_cast<const char*>(v[i]);
}
// Copies insts in state s to the work queue q.
void DFA::StateToWorkq(State* s, Workq* q) {
q->clear();
for (int i = 0; i < s->ninst_; i++) {
if (s->inst_[i] == Mark)
q->mark();
else
q->insert_new(s->inst_[i]);
}
}
// Adds ip to the work queue, following empty arrows according to flag
// and expanding kInstAlt instructions (two-target gotos).
void DFA::AddToQueue(Workq* q, int id, uint flag) {
// Use astack_ to hold our stack of states yet to process.
// It is sized to have room for nastack_ == 2*prog->size() + nmark
// instructions, which is enough: each instruction can be
// processed by the switch below only once, and the processing
// pushes at most two instructions plus maybe a mark.
// (If we're using marks, nmark == prog->size(); otherwise nmark == 0.)
int* stk = astack_;
int nstk = 0;
stk[nstk++] = id;
while (nstk > 0) {
DCHECK_LE(nstk, nastack_);
id = stk[--nstk];
if (id == Mark) {
q->mark();
continue;
}
if (id == 0)
continue;
// If ip is already on the queue, nothing to do.
// Otherwise add it. We don't actually keep all the ones
// that get added -- for example, kInstAlt is ignored
// when on a work queue -- but adding all ip's here
// increases the likelihood of q->contains(id),
// reducing the amount of duplicated work.
if (q->contains(id))
continue;
q->insert_new(id);
// Process instruction.
Prog::Inst* ip = prog_->inst(id);
switch (ip->opcode()) {
case kInstFail: // can't happen: discarded above
break;
case kInstByteRange: // just save these on the queue
case kInstMatch:
break;
case kInstCapture: // DFA treats captures as no-ops.
case kInstNop:
stk[nstk++] = ip->out();
break;
case kInstAlt: // two choices: expand both, in order
case kInstAltMatch:
// Want to visit out then out1, so push on stack in reverse order.
// This instruction is the [00-FF]* loop at the beginning of
// a leftmost-longest unanchored search, separate out from out1
// with a Mark, so that out1's threads (which will start farther
// to the right in the string being searched) are lower priority
// than the current ones.
stk[nstk++] = ip->out1();
if (q->maxmark() > 0 &&
id == prog_->start_unanchored() && id != prog_->start())
stk[nstk++] = Mark;
stk[nstk++] = ip->out();
break;
case kInstEmptyWidth:
if ((ip->empty() & flag) == ip->empty())
stk[nstk++] = ip->out();
break;
}
}
}
// Running of work queues. In the work queue, order matters:
// the queue is sorted in priority order. If instruction i comes before j,
// then the instructions that i produces during the run must come before
// the ones that j produces. In order to keep this invariant, all the
// work queue runners have to take an old queue to process and then
// also a new queue to fill in. It's not acceptable to add to the end of
// an existing queue, because new instructions will not end up in the
// correct position.
// Runs the work queue, processing the empty strings indicated by flag.
// For example, flag == kEmptyBeginLine|kEmptyEndLine means to match
// both ^ and $. It is important that callers pass all flags at once:
// processing both ^ and $ is not the same as first processing only ^
// and then processing only $. Doing the two-step sequence won't match
// ^$^$^$ but processing ^ and $ simultaneously will (and is the behavior
// exhibited by existing implementations).
void DFA::RunWorkqOnEmptyString(Workq* oldq, Workq* newq, uint flag) {
newq->clear();
for (Workq::iterator i = oldq->begin(); i != oldq->end(); ++i) {
if (oldq->is_mark(*i))
AddToQueue(newq, Mark, flag);
else
AddToQueue(newq, *i, flag);
}
}
// Runs the work queue, processing the single byte c followed by any empty
// strings indicated by flag. For example, c == 'a' and flag == kEmptyEndLine,
// means to match c$. Sets the bool *ismatch to true if the end of the
// regular expression program has been reached (the regexp has matched).
void DFA::RunWorkqOnByte(Workq* oldq, Workq* newq,
int c, uint flag, bool* ismatch,
Prog::MatchKind kind,
int new_byte_loop) {
if (DEBUG_MODE)
mutex_.AssertHeld();
newq->clear();
for (Workq::iterator i = oldq->begin(); i != oldq->end(); ++i) {
if (oldq->is_mark(*i)) {
if (*ismatch)
return;
newq->mark();
continue;
}
int id = *i;
Prog::Inst* ip = prog_->inst(id);
switch (ip->opcode()) {
case kInstFail: // never succeeds
case kInstCapture: // already followed
case kInstNop: // already followed
case kInstAlt: // already followed
case kInstAltMatch: // already followed
case kInstEmptyWidth: // already followed
break;
case kInstByteRange: // can follow if c is in range
if (ip->Matches(c))
AddToQueue(newq, ip->out(), flag);
break;
case kInstMatch:
if (prog_->anchor_end() && c != kByteEndText)
break;
*ismatch = true;
if (kind == Prog::kFirstMatch) {
// Can stop processing work queue since we found a match.
return;
}
break;
}
}
if (DebugDFA)
fprintf(stderr, "%s on %d[%#x] -> %s [%d]\n", DumpWorkq(oldq).c_str(),
c, flag, DumpWorkq(newq).c_str(), *ismatch);
}
// Processes input byte c in state, returning new state.
// Caller does not hold mutex.
DFA::State* DFA::RunStateOnByteUnlocked(State* state, int c) {
// Keep only one RunStateOnByte going
// even if the DFA is being run by multiple threads.
MutexLock l(&mutex_);
return RunStateOnByte(state, c);
}
// Processes input byte c in state, returning new state.
DFA::State* DFA::RunStateOnByte(State* state, int c) {
if (DEBUG_MODE)
mutex_.AssertHeld();
if (state <= SpecialStateMax) {
if (state == FullMatchState) {
// It is convenient for routines like PossibleMatchRange
// if we implement RunStateOnByte for FullMatchState:
// once you get into this state you never get out,
// so it's pretty easy.
return FullMatchState;
}
if (state == DeadState) {
LOG(DFATAL) << "DeadState in RunStateOnByte";
return NULL;
}
if (state == NULL) {
LOG(DFATAL) << "NULL state in RunStateOnByte";
return NULL;
}
LOG(DFATAL) << "Unexpected special state in RunStateOnByte";
return NULL;
}
// If someone else already computed this, return it.
MaybeReadMemoryBarrier(); // On alpha we need to ensure read ordering
State* ns = state->next_[ByteMap(c)];
ANNOTATE_HAPPENS_AFTER(ns);
if (ns != NULL)
return ns;
// Convert state into Workq.
StateToWorkq(state, q0_);
// Flags marking the kinds of empty-width things (^ $ etc)
// around this byte. Before the byte we have the flags recorded
// in the State structure itself. After the byte we have
// nothing yet (but that will change: read on).
uint needflag = state->flag_ >> kFlagNeedShift;
uint beforeflag = state->flag_ & kFlagEmptyMask;
uint oldbeforeflag = beforeflag;
uint afterflag = 0;
if (c == '\n') {
// Insert implicit $ and ^ around \n
beforeflag |= kEmptyEndLine;
afterflag |= kEmptyBeginLine;
}
if (c == kByteEndText) {
// Insert implicit $ and \z before the fake "end text" byte.
beforeflag |= kEmptyEndLine | kEmptyEndText;
}
// The state flag kFlagLastWord says whether the last
// byte processed was a word character. Use that info to
// insert empty-width (non-)word boundaries.
bool islastword = state->flag_ & kFlagLastWord;
bool isword = (c != kByteEndText && Prog::IsWordChar(c));
if (isword == islastword)
beforeflag |= kEmptyNonWordBoundary;
else
beforeflag |= kEmptyWordBoundary;
// Okay, finally ready to run.
// Only useful to rerun on empty string if there are new, useful flags.
if (beforeflag & ~oldbeforeflag & needflag) {
RunWorkqOnEmptyString(q0_, q1_, beforeflag);
swap(q0_, q1_);
}
bool ismatch = false;
RunWorkqOnByte(q0_, q1_, c, afterflag, &ismatch, kind_, start_unanchored_);
// Most of the time, we build the state from the output of
// RunWorkqOnByte, so swap q0_ and q1_ here. However, so that
// RE2::Set can tell exactly which match instructions
// contributed to the match, don't swap if c is kByteEndText.
// The resulting state wouldn't be correct for further processing
// of the string, but we're at the end of the text so that's okay.
// Leaving q0_ alone preseves the match instructions that led to
// the current setting of ismatch.
if (c != kByteEndText || kind_ != Prog::kManyMatch)
swap(q0_, q1_);
// Save afterflag along with ismatch and isword in new state.
uint flag = afterflag;
if (ismatch)
flag |= kFlagMatch;
if (isword)
flag |= kFlagLastWord;
ns = WorkqToCachedState(q0_, flag);
// Write barrier before updating state->next_ so that the
// main search loop can proceed without any locking, for speed.
// (Otherwise it would need one mutex operation per input byte.)
// The annotations below tell race detectors that:
// a) the access to next_ should be ignored,
// b) 'ns' is properly published.
WriteMemoryBarrier(); // Flush ns before linking to it.
ANNOTATE_IGNORE_WRITES_BEGIN();
ANNOTATE_HAPPENS_BEFORE(ns);
state->next_[ByteMap(c)] = ns;
ANNOTATE_IGNORE_WRITES_END();
return ns;
}
//////////////////////////////////////////////////////////////////////
// DFA cache reset.
// Reader-writer lock helper.
//
// The DFA uses a reader-writer mutex to protect the state graph itself.
// Traversing the state graph requires holding the mutex for reading,
// and discarding the state graph and starting over requires holding the
// lock for writing. If a search needs to expand the graph but is out
// of memory, it will need to drop its read lock and then acquire the
// write lock. Since it cannot then atomically downgrade from write lock
// to read lock, it runs the rest of the search holding the write lock.
// (This probably helps avoid repeated contention, but really the decision
// is forced by the Mutex interface.) It's a bit complicated to keep
// track of whether the lock is held for reading or writing and thread
// that through the search, so instead we encapsulate it in the RWLocker
// and pass that around.
class DFA::RWLocker {
public:
explicit RWLocker(Mutex* mu);
~RWLocker();
// If the lock is only held for reading right now,
// drop the read lock and re-acquire for writing.
// Subsequent calls to LockForWriting are no-ops.
// Notice that the lock is *released* temporarily.
void LockForWriting();
// Returns whether the lock is already held for writing.
bool IsLockedForWriting() {
return writing_;
}
private:
Mutex* mu_;
bool writing_;
DISALLOW_EVIL_CONSTRUCTORS(RWLocker);
};
DFA::RWLocker::RWLocker(Mutex* mu)
: mu_(mu), writing_(false) {
mu_->ReaderLock();
}
// This function is marked as NO_THREAD_SAFETY_ANALYSIS because the annotations
// does not support lock upgrade.
void DFA::RWLocker::LockForWriting() NO_THREAD_SAFETY_ANALYSIS {
if (!writing_) {
mu_->ReaderUnlock();
mu_->Lock();
writing_ = true;
}
}
DFA::RWLocker::~RWLocker() {
if (writing_)
mu_->WriterUnlock();
else
mu_->ReaderUnlock();
}
// When the DFA's State cache fills, we discard all the states in the
// cache and start over. Many threads can be using and adding to the
// cache at the same time, so we synchronize using the cache_mutex_
// to keep from stepping on other threads. Specifically, all the
// threads using the current cache hold cache_mutex_ for reading.
// When a thread decides to flush the cache, it drops cache_mutex_
// and then re-acquires it for writing. That ensures there are no
// other threads accessing the cache anymore. The rest of the search
// runs holding cache_mutex_ for writing, avoiding any contention
// with or cache pollution caused by other threads.
void DFA::ResetCache(RWLocker* cache_lock) {
// Re-acquire the cache_mutex_ for writing (exclusive use).
bool was_writing = cache_lock->IsLockedForWriting();
cache_lock->LockForWriting();
// If we already held cache_mutex_ for writing, it means
// this invocation of Search() has already reset the
// cache once already. That's a pretty clear indication
// that the cache is too small. Warn about that, once.
// TODO(rsc): Only warn if state_cache_.size() < some threshold.
if (was_writing && !cache_warned_) {
LOG(INFO) << "DFA memory cache could be too small: "
<< "only room for " << state_cache_.size() << " states.";
cache_warned_ = true;
}
// Clear the cache, reset the memory budget.
for (int i = 0; i < kMaxStart; i++) {
start_[i].start = NULL;
start_[i].firstbyte = kFbUnknown;
}
ClearCache();
mem_budget_ = state_budget_;
}
// Typically, a couple States do need to be preserved across a cache
// reset, like the State at the current point in the search.
// The StateSaver class helps keep States across cache resets.
// It makes a copy of the state's guts outside the cache (before the reset)
// and then can be asked, after the reset, to recreate the State
// in the new cache. For example, in a DFA method ("this" is a DFA):
//
// StateSaver saver(this, s);
// ResetCache(cache_lock);
// s = saver.Restore();
//
// The saver should always have room in the cache to re-create the state,
// because resetting the cache locks out all other threads, and the cache
// is known to have room for at least a couple states (otherwise the DFA
// constructor fails).
class DFA::StateSaver {
public:
explicit StateSaver(DFA* dfa, State* state);
~StateSaver();
// Recreates and returns a state equivalent to the
// original state passed to the constructor.
// Returns NULL if the cache has filled, but
// since the DFA guarantees to have room in the cache
// for a couple states, should never return NULL
// if used right after ResetCache.
State* Restore();
private:
DFA* dfa_; // the DFA to use
int* inst_; // saved info from State
int ninst_;
uint flag_;
bool is_special_; // whether original state was special
State* special_; // if is_special_, the original state
DISALLOW_EVIL_CONSTRUCTORS(StateSaver);
};
DFA::StateSaver::StateSaver(DFA* dfa, State* state) {
dfa_ = dfa;
if (state <= SpecialStateMax) {
inst_ = NULL;
ninst_ = 0;
flag_ = 0;
is_special_ = true;
special_ = state;
return;
}
is_special_ = false;
special_ = NULL;
flag_ = state->flag_;
ninst_ = state->ninst_;
inst_ = new int[ninst_];
memmove(inst_, state->inst_, ninst_*sizeof inst_[0]);
}
DFA::StateSaver::~StateSaver() {
if (!is_special_)
delete[] inst_;
}
DFA::State* DFA::StateSaver::Restore() {
if (is_special_)
return special_;
MutexLock l(&dfa_->mutex_);
State* s = dfa_->CachedState(inst_, ninst_, flag_);
if (s == NULL)
LOG(DFATAL) << "StateSaver failed to restore state.";
return s;
}
//////////////////////////////////////////////////////////////////////
//
// DFA execution.
//
// The basic search loop is easy: start in a state s and then for each
// byte c in the input, s = s->next[c].
//
// This simple description omits a few efficiency-driven complications.
//
// First, the State graph is constructed incrementally: it is possible
// that s->next[c] is null, indicating that that state has not been
// fully explored. In this case, RunStateOnByte must be invoked to
// determine the next state, which is cached in s->next[c] to save
// future effort. An alternative reason for s->next[c] to be null is
// that the DFA has reached a so-called "dead state", in which any match
// is no longer possible. In this case RunStateOnByte will return NULL
// and the processing of the string can stop early.
//
// Second, a 256-element pointer array for s->next_ makes each State
// quite large (2kB on 64-bit machines). Instead, dfa->bytemap_[]
// maps from bytes to "byte classes" and then next_ only needs to have
// as many pointers as there are byte classes. A byte class is simply a
// range of bytes that the regexp never distinguishes between.
// A regexp looking for a[abc] would have four byte ranges -- 0 to 'a'-1,
// 'a', 'b' to 'c', and 'c' to 0xFF. The bytemap slows us a little bit
// but in exchange we typically cut the size of a State (and thus our
// memory footprint) by about 5-10x. The comments still refer to
// s->next[c] for simplicity, but code should refer to s->next_[bytemap_[c]].
//
// Third, it is common for a DFA for an unanchored match to begin in a
// state in which only one particular byte value can take the DFA to a
// different state. That is, s->next[c] != s for only one c. In this
// situation, the DFA can do better than executing the simple loop.
// Instead, it can call memchr to search very quickly for the byte c.
// Whether the start state has this property is determined during a
// pre-compilation pass, and if so, the byte b is passed to the search
// loop as the "firstbyte" argument, along with a boolean "have_firstbyte".
//
// Fourth, the desired behavior is to search for the leftmost-best match
// (approximately, the same one that Perl would find), which is not
// necessarily the match ending earliest in the string. Each time a
// match is found, it must be noted, but the DFA must continue on in
// hope of finding a higher-priority match. In some cases, the caller only
// cares whether there is any match at all, not which one is found.
// The "want_earliest_match" flag causes the search to stop at the first
// match found.
//
// Fifth, one algorithm that uses the DFA needs it to run over the
// input string backward, beginning at the end and ending at the beginning.
// Passing false for the "run_forward" flag causes the DFA to run backward.
//
// The checks for these last three cases, which in a naive implementation
// would be performed once per input byte, slow the general loop enough
// to merit specialized versions of the search loop for each of the
// eight possible settings of the three booleans. Rather than write
// eight different functions, we write one general implementation and then
// inline it to create the specialized ones.
//
// Note that matches are delayed by one byte, to make it easier to
// accomodate match conditions depending on the next input byte (like $ and \b).
// When s->next[c]->IsMatch(), it means that there is a match ending just
// *before* byte c.
// The generic search loop. Searches text for a match, returning
// the pointer to the end of the chosen match, or NULL if no match.
// The bools are equal to the same-named variables in params, but
// making them function arguments lets the inliner specialize
// this function to each combination (see two paragraphs above).
inline bool DFA::InlinedSearchLoop(SearchParams* params,
bool have_firstbyte,
bool want_earliest_match,
bool run_forward) {
State* start = params->start;
const uint8* bp = BytePtr(params->text.begin()); // start of text
const uint8* p = bp; // text scanning point
const uint8* ep = BytePtr(params->text.end()); // end of text
const uint8* resetp = NULL; // p at last cache reset
if (!run_forward)
swap(p, ep);
const uint8* bytemap = prog_->bytemap();
const uint8* lastmatch = NULL; // most recent matching position in text
bool matched = false;
State* s = start;
if (s->IsMatch()) {
matched = true;
lastmatch = p;
if (want_earliest_match) {
params->ep = reinterpret_cast<const char*>(lastmatch);
return true;
}
}
while (p != ep) {
if (DebugDFA)
fprintf(stderr, "@%d: %s\n", static_cast<int>(p - bp),
DumpState(s).c_str());
if (have_firstbyte && s == start) {
// In start state, only way out is to find firstbyte,
// so use optimized assembly in memchr to skip ahead.
// If firstbyte isn't found, we can skip to the end
// of the string.
if (run_forward) {
if ((p = BytePtr(memchr(p, params->firstbyte, ep - p))) == NULL) {
p = ep;
break;
}
} else {
if ((p = BytePtr(memrchr(ep, params->firstbyte, p - ep))) == NULL) {
p = ep;
break;
}
p++;
}
}
int c;
if (run_forward)
c = *p++;
else
c = *--p;
// Note that multiple threads might be consulting
// s->next_[bytemap[c]] simultaneously.
// RunStateOnByte takes care of the appropriate locking,
// including a memory barrier so that the unlocked access
// (sometimes known as "double-checked locking") is safe.
// The alternative would be either one DFA per thread
// or one mutex operation per input byte.
//
// ns == DeadState means the state is known to be dead
// (no more matches are possible).
// ns == NULL means the state has not yet been computed
// (need to call RunStateOnByteUnlocked).
// RunStateOnByte returns ns == NULL if it is out of memory.
// ns == FullMatchState means the rest of the string matches.
//
// Okay to use bytemap[] not ByteMap() here, because
// c is known to be an actual byte and not kByteEndText.
MaybeReadMemoryBarrier(); // On alpha we need to ensure read ordering
State* ns = s->next_[bytemap[c]];
ANNOTATE_HAPPENS_AFTER(ns);
if (ns == NULL) {
ns = RunStateOnByteUnlocked(s, c);
if (ns == NULL) {
// After we reset the cache, we hold cache_mutex exclusively,
// so if resetp != NULL, it means we filled the DFA state
// cache with this search alone (without any other threads).
// Benchmarks show that doing a state computation on every
// byte runs at about 0.2 MB/s, while the NFA (nfa.cc) can do the
// same at about 2 MB/s. Unless we're processing an average
// of 10 bytes per state computation, fail so that RE2 can
// fall back to the NFA.
if (FLAGS_re2_dfa_bail_when_slow && resetp != NULL &&
(p - resetp) < 10*state_cache_.size()) {
params->failed = true;
return false;
}
resetp = p;
// Prepare to save start and s across the reset.
StateSaver save_start(this, start);
StateSaver save_s(this, s);
// Discard all the States in the cache.
ResetCache(params->cache_lock);
// Restore start and s so we can continue.
if ((start = save_start.Restore()) == NULL ||
(s = save_s.Restore()) == NULL) {
// Restore already did LOG(DFATAL).
params->failed = true;
return false;
}
ns = RunStateOnByteUnlocked(s, c);
if (ns == NULL) {
LOG(DFATAL) << "RunStateOnByteUnlocked failed after ResetCache";
params->failed = true;
return false;
}
}
}
if (ns <= SpecialStateMax) {
if (ns == DeadState) {
params->ep = reinterpret_cast<const char*>(lastmatch);
return matched;
}
// FullMatchState
params->ep = reinterpret_cast<const char*>(ep);
return true;
}
s = ns;
if (s->IsMatch()) {
matched = true;
// The DFA notices the match one byte late,
// so adjust p before using it in the match.
if (run_forward)
lastmatch = p - 1;
else
lastmatch = p + 1;
if (DebugDFA)
fprintf(stderr, "match @%d! [%s]\n",
static_cast<int>(lastmatch - bp),
DumpState(s).c_str());
if (want_earliest_match) {
params->ep = reinterpret_cast<const char*>(lastmatch);
return true;
}
}
}
// Process one more byte to see if it triggers a match.
// (Remember, matches are delayed one byte.)
int lastbyte;
if (run_forward) {
if (params->text.end() == params->context.end())
lastbyte = kByteEndText;
else
lastbyte = params->text.end()[0] & 0xFF;
} else {
if (params->text.begin() == params->context.begin())
lastbyte = kByteEndText;
else
lastbyte = params->text.begin()[-1] & 0xFF;
}
MaybeReadMemoryBarrier(); // On alpha we need to ensure read ordering
State* ns = s->next_[ByteMap(lastbyte)];
ANNOTATE_HAPPENS_AFTER(ns);
if (ns == NULL) {
ns = RunStateOnByteUnlocked(s, lastbyte);
if (ns == NULL) {
StateSaver save_s(this, s);
ResetCache(params->cache_lock);
if ((s = save_s.Restore()) == NULL) {
params->failed = true;
return false;
}
ns = RunStateOnByteUnlocked(s, lastbyte);
if (ns == NULL) {
LOG(DFATAL) << "RunStateOnByteUnlocked failed after Reset";
params->failed = true;
return false;
}
}
}
s = ns;
if (DebugDFA)
fprintf(stderr, "@_: %s\n", DumpState(s).c_str());
if (s == FullMatchState) {
params->ep = reinterpret_cast<const char*>(ep);
return true;
}
if (s > SpecialStateMax && s->IsMatch()) {
matched = true;
lastmatch = p;
if (params->matches && kind_ == Prog::kManyMatch) {
vector<int>* v = params->matches;
v->clear();
for (int i = 0; i < s->ninst_; i++) {
Prog::Inst* ip = prog_->inst(s->inst_[i]);
if (ip->opcode() == kInstMatch)
v->push_back(ip->match_id());
}
}
if (DebugDFA)
fprintf(stderr, "match @%d! [%s]\n", static_cast<int>(lastmatch - bp),
DumpState(s).c_str());
}
params->ep = reinterpret_cast<const char*>(lastmatch);
return matched;
}
// Inline specializations of the general loop.
bool DFA::SearchFFF(SearchParams* params) {
return InlinedSearchLoop(params, 0, 0, 0);
}
bool DFA::SearchFFT(SearchParams* params) {
return InlinedSearchLoop(params, 0, 0, 1);
}
bool DFA::SearchFTF(SearchParams* params) {
return InlinedSearchLoop(params, 0, 1, 0);
}
bool DFA::SearchFTT(SearchParams* params) {
return InlinedSearchLoop(params, 0, 1, 1);
}
bool DFA::SearchTFF(SearchParams* params) {
return InlinedSearchLoop(params, 1, 0, 0);
}
bool DFA::SearchTFT(SearchParams* params) {
return InlinedSearchLoop(params, 1, 0, 1);
}
bool DFA::SearchTTF(SearchParams* params) {
return InlinedSearchLoop(params, 1, 1, 0);
}
bool DFA::SearchTTT(SearchParams* params) {
return InlinedSearchLoop(params, 1, 1, 1);
}
// For debugging, calls the general code directly.
bool DFA::SlowSearchLoop(SearchParams* params) {
return InlinedSearchLoop(params,
params->firstbyte >= 0,
params->want_earliest_match,
params->run_forward);
}
// For performance, calls the appropriate specialized version
// of InlinedSearchLoop.
bool DFA::FastSearchLoop(SearchParams* params) {
// Because the methods are private, the Searches array
// cannot be declared at top level.
static bool (DFA::*Searches[])(SearchParams*) = {
&DFA::SearchFFF,
&DFA::SearchFFT,
&DFA::SearchFTF,
&DFA::SearchFTT,
&DFA::SearchTFF,
&DFA::SearchTFT,
&DFA::SearchTTF,
&DFA::SearchTTT,
};
bool have_firstbyte = (params->firstbyte >= 0);
int index = 4 * have_firstbyte +
2 * params->want_earliest_match +
1 * params->run_forward;
return (this->*Searches[index])(params);
}
// The discussion of DFA execution above ignored the question of how
// to determine the initial state for the search loop. There are two
// factors that influence the choice of start state.
//
// The first factor is whether the search is anchored or not.
// The regexp program (Prog*) itself has
// two different entry points: one for anchored searches and one for
// unanchored searches. (The unanchored version starts with a leading ".*?"
// and then jumps to the anchored one.)
//
// The second factor is where text appears in the larger context, which
// determines which empty-string operators can be matched at the beginning
// of execution. If text is at the very beginning of context, \A and ^ match.
// Otherwise if text is at the beginning of a line, then ^ matches.
// Otherwise it matters whether the character before text is a word character
// or a non-word character.
//
// The two cases (unanchored vs not) and four cases (empty-string flags)
// combine to make the eight cases recorded in the DFA's begin_text_[2],
// begin_line_[2], after_wordchar_[2], and after_nonwordchar_[2] cached
// StartInfos. The start state for each is filled in the first time it
// is used for an actual search.
// Examines text, context, and anchored to determine the right start
// state for the DFA search loop. Fills in params and returns true on success.
// Returns false on failure.
bool DFA::AnalyzeSearch(SearchParams* params) {
const StringPiece& text = params->text;
const StringPiece& context = params->context;
// Sanity check: make sure that text lies within context.
if (text.begin() < context.begin() || text.end() > context.end()) {
LOG(DFATAL) << "Text is not inside context.";
params->start = DeadState;
return true;
}
// Determine correct search type.
int start;
uint flags;
if (params->run_forward) {
if (text.begin() == context.begin()) {
start = kStartBeginText;
flags = kEmptyBeginText|kEmptyBeginLine;
} else if (text.begin()[-1] == '\n') {
start = kStartBeginLine;
flags = kEmptyBeginLine;
} else if (Prog::IsWordChar(text.begin()[-1] & 0xFF)) {
start = kStartAfterWordChar;
flags = kFlagLastWord;
} else {
start = kStartAfterNonWordChar;
flags = 0;
}
} else {
if (text.end() == context.end()) {
start = kStartBeginText;
flags = kEmptyBeginText|kEmptyBeginLine;
} else if (text.end()[0] == '\n') {
start = kStartBeginLine;
flags = kEmptyBeginLine;
} else if (Prog::IsWordChar(text.end()[0] & 0xFF)) {
start = kStartAfterWordChar;
flags = kFlagLastWord;
} else {
start = kStartAfterNonWordChar;
flags = 0;
}
}
if (params->anchored || prog_->anchor_start())
start |= kStartAnchored;
StartInfo* info = &start_[start];
// Try once without cache_lock for writing.
// Try again after resetting the cache
// (ResetCache will relock cache_lock for writing).
if (!AnalyzeSearchHelper(params, info, flags)) {
ResetCache(params->cache_lock);
if (!AnalyzeSearchHelper(params, info, flags)) {
LOG(DFATAL) << "Failed to analyze start state.";
params->failed = true;
return false;
}
}
if (DebugDFA)
fprintf(stderr, "anchored=%d fwd=%d flags=%#x state=%s firstbyte=%d\n",
params->anchored, params->run_forward, flags,
DumpState(info->start).c_str(), info->firstbyte);
params->start = info->start;
params->firstbyte = ANNOTATE_UNPROTECTED_READ(info->firstbyte);
return true;
}
// Fills in info if needed. Returns true on success, false on failure.
bool DFA::AnalyzeSearchHelper(SearchParams* params, StartInfo* info,
uint flags) {
// Quick check; okay because of memory barriers below.
if (ANNOTATE_UNPROTECTED_READ(info->firstbyte) != kFbUnknown) {
ANNOTATE_HAPPENS_AFTER(&info->firstbyte);
return true;
}
MutexLock l(&mutex_);
if (info->firstbyte != kFbUnknown) {
ANNOTATE_HAPPENS_AFTER(&info->firstbyte);
return true;
}
q0_->clear();
AddToQueue(q0_,
params->anchored ? prog_->start() : prog_->start_unanchored(),
flags);
info->start = WorkqToCachedState(q0_, flags);
if (info->start == NULL)
return false;
if (info->start == DeadState) {
ANNOTATE_HAPPENS_BEFORE(&info->firstbyte);
WriteMemoryBarrier(); // Synchronize with "quick check" above.
info->firstbyte = kFbNone;
return true;
}
if (info->start == FullMatchState) {
ANNOTATE_HAPPENS_BEFORE(&info->firstbyte);
WriteMemoryBarrier(); // Synchronize with "quick check" above.
info->firstbyte = kFbNone; // will be ignored
return true;
}
// Compute info->firstbyte by running state on all
// possible byte values, looking for a single one that
// leads to a different state.
int firstbyte = kFbNone;
for (int i = 0; i < 256; i++) {
State* s = RunStateOnByte(info->start, i);
if (s == NULL) {
ANNOTATE_HAPPENS_BEFORE(&info->firstbyte);
WriteMemoryBarrier(); // Synchronize with "quick check" above.
info->firstbyte = firstbyte;
return false;
}
if (s == info->start)
continue;
// Goes to new state...
if (firstbyte == kFbNone) {
firstbyte = i; // ... first one
} else {
firstbyte = kFbMany; // ... too many
break;
}
}
ANNOTATE_HAPPENS_BEFORE(&info->firstbyte);
WriteMemoryBarrier(); // Synchronize with "quick check" above.
info->firstbyte = firstbyte;
return true;
}
// The actual DFA search: calls AnalyzeSearch and then FastSearchLoop.
bool DFA::Search(const StringPiece& text,
const StringPiece& context,
bool anchored,
bool want_earliest_match,
bool run_forward,
bool* failed,
const char** epp,
vector<int>* matches) {
*epp = NULL;
if (!ok()) {
*failed = true;
return false;
}
*failed = false;
if (DebugDFA) {
fprintf(stderr, "\nprogram:\n%s\n", prog_->DumpUnanchored().c_str());
fprintf(stderr, "text %s anchored=%d earliest=%d fwd=%d kind %d\n",
text.as_string().c_str(), anchored, want_earliest_match,
run_forward, kind_);
}
RWLocker l(&cache_mutex_);
SearchParams params(text, context, &l);
params.anchored = anchored;
params.want_earliest_match = want_earliest_match;
params.run_forward = run_forward;
params.matches = matches;
if (!AnalyzeSearch(¶ms)) {
*failed = true;
return false;
}
if (params.start == DeadState)
return false;
if (params.start == FullMatchState) {
if (run_forward == want_earliest_match)
*epp = text.begin();
else
*epp = text.end();
return true;
}
if (DebugDFA)
fprintf(stderr, "start %s\n", DumpState(params.start).c_str());
bool ret = FastSearchLoop(¶ms);
if (params.failed) {
*failed = true;
return false;
}
*epp = params.ep;
return ret;
}
// Deletes dfa.
//
// This is a separate function so that
// prog.h can be used without moving the definition of
// class DFA out of this file. If you set
// prog->dfa_ = dfa;
// then you also have to set
// prog->delete_dfa_ = DeleteDFA;
// so that ~Prog can delete the dfa.
static void DeleteDFA(DFA* dfa) {
delete dfa;
}
DFA* Prog::GetDFA(MatchKind kind) {
DFA*volatile* pdfa;
if (kind == kFirstMatch || kind == kManyMatch) {
pdfa = &dfa_first_;
} else {
kind = kLongestMatch;
pdfa = &dfa_longest_;
}
// Quick check; okay because of memory barrier below.
DFA *dfa = ANNOTATE_UNPROTECTED_READ(*pdfa);
if (dfa != NULL) {
ANNOTATE_HAPPENS_AFTER(dfa);
return dfa;
}
MutexLock l(&dfa_mutex_);
dfa = *pdfa;
if (dfa != NULL) {
ANNOTATE_HAPPENS_AFTER(dfa);
return dfa;
}
// For a forward DFA, half the memory goes to each DFA.
// For a reverse DFA, all the memory goes to the
// "longest match" DFA, because RE2 never does reverse
// "first match" searches.
int64 m = dfa_mem_/2;
if (reversed_) {
if (kind == kLongestMatch || kind == kManyMatch)
m = dfa_mem_;
else
m = 0;
}
dfa = new DFA(this, kind, m);
delete_dfa_ = DeleteDFA;
// Synchronize with "quick check" above.
ANNOTATE_HAPPENS_BEFORE(dfa);
WriteMemoryBarrier();
*pdfa = dfa;
return dfa;
}
// Executes the regexp program to search in text,
// which itself is inside the larger context. (As a convenience,
// passing a NULL context is equivalent to passing text.)
// Returns true if a match is found, false if not.
// If a match is found, fills in match0->end() to point at the end of the match
// and sets match0->begin() to text.begin(), since the DFA can't track
// where the match actually began.
//
// This is the only external interface (class DFA only exists in this file).
//
bool Prog::SearchDFA(const StringPiece& text, const StringPiece& const_context,
Anchor anchor, MatchKind kind,
StringPiece* match0, bool* failed, vector<int>* matches) {
*failed = false;
StringPiece context = const_context;
if (context.begin() == NULL)
context = text;
bool carat = anchor_start();
bool dollar = anchor_end();
if (reversed_) {
bool t = carat;
carat = dollar;
dollar = t;
}
if (carat && context.begin() != text.begin())
return false;
if (dollar && context.end() != text.end())
return false;
// Handle full match by running an anchored longest match
// and then checking if it covers all of text.
bool anchored = anchor == kAnchored || anchor_start() || kind == kFullMatch;
bool endmatch = false;
if (kind == kManyMatch) {
endmatch = true;
} else if (kind == kFullMatch || anchor_end()) {
endmatch = true;
kind = kLongestMatch;
}
// If the caller doesn't care where the match is (just whether one exists),
// then we can stop at the very first match we find, the so-called
// "shortest match".
bool want_shortest_match = false;
if (match0 == NULL && !endmatch) {
want_shortest_match = true;
kind = kLongestMatch;
}
DFA* dfa = GetDFA(kind);
const char* ep;
bool matched = dfa->Search(text, context, anchored,
want_shortest_match, !reversed_,
failed, &ep, matches);
if (*failed)
return false;
if (!matched)
return false;
if (endmatch && ep != (reversed_ ? text.begin() : text.end()))
return false;
// If caller cares, record the boundary of the match.
// We only know where it ends, so use the boundary of text
// as the beginning.
if (match0) {
if (reversed_)
*match0 = StringPiece(ep, text.end() - ep);
else
*match0 = StringPiece(text.begin(), ep - text.begin());
}
return true;
}
// Build out all states in DFA. Returns number of states.
int DFA::BuildAllStates() {
if (!ok())
return 0;
// Pick out start state for unanchored search
// at beginning of text.
RWLocker l(&cache_mutex_);
SearchParams params(NULL, NULL, &l);
params.anchored = false;
if (!AnalyzeSearch(¶ms) || params.start <= SpecialStateMax)
return 0;
// Add start state to work queue.
StateSet queued;
vector<State*> q;
queued.insert(params.start);
q.push_back(params.start);
// Flood to expand every state.
for (int i = 0; i < q.size(); i++) {
State* s = q[i];
for (int c = 0; c < 257; c++) {
State* ns = RunStateOnByteUnlocked(s, c);
if (ns > SpecialStateMax && queued.find(ns) == queued.end()) {
queued.insert(ns);
q.push_back(ns);
}
}
}
return q.size();
}
// Build out all states in DFA for kind. Returns number of states.
int Prog::BuildEntireDFA(MatchKind kind) {
//LOG(ERROR) << "BuildEntireDFA is only for testing.";
return GetDFA(kind)->BuildAllStates();
}
// Computes min and max for matching string.
// Won't return strings bigger than maxlen.
bool DFA::PossibleMatchRange(string* min, string* max, int maxlen) {
if (!ok())
return false;
// NOTE: if future users of PossibleMatchRange want more precision when
// presented with infinitely repeated elements, consider making this a
// parameter to PossibleMatchRange.
static int kMaxEltRepetitions = 0;
// Keep track of the number of times we've visited states previously. We only
// revisit a given state if it's part of a repeated group, so if the value
// portion of the map tuple exceeds kMaxEltRepetitions we bail out and set
// |*max| to |PrefixSuccessor(*max)|.
//
// Also note that previously_visited_states[UnseenStatePtr] will, in the STL
// tradition, implicitly insert a '0' value at first use. We take advantage
// of that property below.
map<State*, int> previously_visited_states;
// Pick out start state for anchored search at beginning of text.
RWLocker l(&cache_mutex_);
SearchParams params(NULL, NULL, &l);
params.anchored = true;
if (!AnalyzeSearch(¶ms))
return false;
if (params.start == DeadState) { // No matching strings
*min = "";
*max = "";
return true;
}
if (params.start == FullMatchState) // Every string matches: no max
return false;
// The DFA is essentially a big graph rooted at params.start,
// and paths in the graph correspond to accepted strings.
// Each node in the graph has potentially 256+1 arrows
// coming out, one for each byte plus the magic end of
// text character kByteEndText.
// To find the smallest possible prefix of an accepted
// string, we just walk the graph preferring to follow
// arrows with the lowest bytes possible. To find the
// largest possible prefix, we follow the largest bytes
// possible.
// The test for whether there is an arrow from s on byte j is
// ns = RunStateOnByteUnlocked(s, j);
// if (ns == NULL)
// return false;
// if (ns != DeadState && ns->ninst > 0)
// The RunStateOnByteUnlocked call asks the DFA to build out the graph.
// It returns NULL only if the DFA has run out of memory,
// in which case we can't be sure of anything.
// The second check sees whether there was graph built
// and whether it is interesting graph. Nodes might have
// ns->ninst == 0 if they exist only to represent the fact
// that a match was found on the previous byte.
// Build minimum prefix.
State* s = params.start;
min->clear();
for (int i = 0; i < maxlen; i++) {
if (previously_visited_states[s] > kMaxEltRepetitions) {
VLOG(2) << "Hit kMaxEltRepetitions=" << kMaxEltRepetitions
<< " for state s=" << s << " and min=" << CEscape(*min);
break;
}
previously_visited_states[s]++;
// Stop if min is a match.
State* ns = RunStateOnByteUnlocked(s, kByteEndText);
if (ns == NULL) // DFA out of memory
return false;
if (ns != DeadState && (ns == FullMatchState || ns->IsMatch()))
break;
// Try to extend the string with low bytes.
bool extended = false;
for (int j = 0; j < 256; j++) {
ns = RunStateOnByteUnlocked(s, j);
if (ns == NULL) // DFA out of memory
return false;
if (ns == FullMatchState ||
(ns > SpecialStateMax && ns->ninst_ > 0)) {
extended = true;
min->append(1, j);
s = ns;
break;
}
}
if (!extended)
break;
}
// Build maximum prefix.
previously_visited_states.clear();
s = params.start;
max->clear();
for (int i = 0; i < maxlen; i++) {
if (previously_visited_states[s] > kMaxEltRepetitions) {
VLOG(2) << "Hit kMaxEltRepetitions=" << kMaxEltRepetitions
<< " for state s=" << s << " and max=" << CEscape(*max);
break;
}
previously_visited_states[s] += 1;
// Try to extend the string with high bytes.
bool extended = false;
for (int j = 255; j >= 0; j--) {
State* ns = RunStateOnByteUnlocked(s, j);
if (ns == NULL)
return false;
if (ns == FullMatchState ||
(ns > SpecialStateMax && ns->ninst_ > 0)) {
extended = true;
max->append(1, j);
s = ns;
break;
}
}
if (!extended) {
// Done, no need for PrefixSuccessor.
return true;
}
}
// Stopped while still adding to *max - round aaaaaaaaaa... to aaaa...b
*max = PrefixSuccessor(*max);
// If there are no bytes left, we have no way to say "there is no maximum
// string". We could make the interface more complicated and be able to
// return "there is no maximum but here is a minimum", but that seems like
// overkill -- the most common no-max case is all possible strings, so not
// telling the caller that the empty string is the minimum match isn't a
// great loss.
if (max->empty())
return false;
return true;
}
// PossibleMatchRange for a Prog.
bool Prog::PossibleMatchRange(string* min, string* max, int maxlen) {
DFA* dfa = NULL;
{
MutexLock l(&dfa_mutex_);
// Have to use dfa_longest_ to get all strings for full matches.
// For example, (a|aa) never matches aa in first-match mode.
if (dfa_longest_ == NULL) {
dfa_longest_ = new DFA(this, Prog::kLongestMatch, dfa_mem_/2);
delete_dfa_ = DeleteDFA;
}
dfa = dfa_longest_;
}
return dfa->PossibleMatchRange(min, max, maxlen);
}
} // namespace re2