// Copyright (c) 2008, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// ---
// Author: Sanjay Ghemawat <opensource@google.com>
#ifndef TCMALLOC_THREAD_CACHE_H_
#define TCMALLOC_THREAD_CACHE_H_
#include <config.h>
#ifdef HAVE_PTHREAD
#include <pthread.h> // for pthread_t, pthread_key_t
#endif
#include <stddef.h> // for size_t, NULL
#ifdef HAVE_STDINT_H
#include <stdint.h> // for uint32_t, uint64_t
#endif
#include <sys/types.h> // for ssize_t
#include "common.h"
#include "linked_list.h"
#include "maybe_threads.h"
#include "page_heap_allocator.h"
#include "sampler.h"
#include "static_vars.h"
#include "common.h" // for SizeMap, kMaxSize, etc
#include "internal_logging.h" // for ASSERT, etc
#include "linked_list.h" // for SLL_Pop, SLL_PopRange, etc
#include "page_heap_allocator.h" // for PageHeapAllocator
#include "sampler.h" // for Sampler
#include "static_vars.h" // for Static
namespace tcmalloc {
// Even if we have support for thread-local storage in the compiler
// and linker, the OS may not support it. We need to check that at
// runtime. Right now, we have to keep a manual set of "bad" OSes.
#if defined(HAVE_TLS)
extern bool kernel_supports_tls; // defined in thread_cache.cc
void CheckIfKernelSupportsTLS();
inline bool KernelSupportsTLS() {
return kernel_supports_tls;
}
#endif // HAVE_TLS
//-------------------------------------------------------------------
// Data kept per thread
//-------------------------------------------------------------------
class ThreadCache {
public:
// All ThreadCache objects are kept in a linked list (for stats collection)
ThreadCache* next_;
ThreadCache* prev_;
void Init(pthread_t tid);
void Cleanup();
// Accessors (mostly just for printing stats)
int freelist_length(size_t cl) const { return list_[cl].length(); }
// Total byte size in cache
size_t Size() const { return size_; }
// Allocate an object of the given size and class. The size given
// must be the same as the size of the class in the size map.
void* Allocate(size_t size, size_t cl);
void Deallocate(void* ptr, size_t size_class);
void Scavenge();
int GetSamplePeriod();
// Record allocation of "k" bytes. Return true iff allocation
// should be sampled
bool SampleAllocation(size_t k);
static void InitModule();
static void InitTSD();
static ThreadCache* GetThreadHeap();
static ThreadCache* GetCache();
static ThreadCache* GetCacheIfPresent();
static ThreadCache* CreateCacheIfNecessary();
static void BecomeIdle();
// Return the number of thread heaps in use.
static inline int HeapsInUse();
// Writes to total_bytes the total number of bytes used by all thread heaps.
// class_count must be an array of size kNumClasses. Writes the number of
// items on the corresponding freelist. class_count may be NULL.
// The storage of both parameters must be zero intialized.
// REQUIRES: Static::pageheap_lock is held.
static void GetThreadStats(uint64_t* total_bytes, uint64_t* class_count);
// Sets the total thread cache size to new_size, recomputing the
// individual thread cache sizes as necessary.
// REQUIRES: Static::pageheap lock is held.
static void set_overall_thread_cache_size(size_t new_size);
static size_t overall_thread_cache_size() {
return overall_thread_cache_size_;
}
private:
class FreeList {
private:
void* list_; // Linked list of nodes
#ifdef _LP64
// On 64-bit hardware, manipulating 16-bit values may be slightly slow.
uint32_t length_; // Current length.
uint32_t lowater_; // Low water mark for list length.
uint32_t max_length_; // Dynamic max list length based on usage.
// Tracks the number of times a deallocation has caused
// length_ > max_length_. After the kMaxOverages'th time, max_length_
// shrinks and length_overages_ is reset to zero.
uint32_t length_overages_;
#else
// If we aren't using 64-bit pointers then pack these into less space.
uint16_t length_;
uint16_t lowater_;
uint16_t max_length_;
uint16_t length_overages_;
#endif
public:
void Init() {
list_ = NULL;
length_ = 0;
lowater_ = 0;
max_length_ = 1;
length_overages_ = 0;
}
// Return current length of list
size_t length() const {
return length_;
}
// Return the maximum length of the list.
size_t max_length() const {
return max_length_;
}
// Set the maximum length of the list. If 'new_max' > length(), the
// client is responsible for removing objects from the list.
void set_max_length(size_t new_max) {
max_length_ = new_max;
}
// Return the number of times that length() has gone over max_length().
size_t length_overages() const {
return length_overages_;
}
void set_length_overages(size_t new_count) {
length_overages_ = new_count;
}
// Is list empty?
bool empty() const {
return list_ == NULL;
}
// Low-water mark management
int lowwatermark() const { return lowater_; }
void clear_lowwatermark() { lowater_ = length_; }
void Push(void* ptr) {
SLL_Push(&list_, ptr);
length_++;
}
void* Pop() {
ASSERT(list_ != NULL);
length_--;
if (length_ < lowater_) lowater_ = length_;
return SLL_Pop(&list_);
}
void* Next() {
return SLL_Next(&list_);
}
void PushRange(int N, void *start, void *end) {
SLL_PushRange(&list_, start, end);
length_ += N;
}
void PopRange(int N, void **start, void **end) {
SLL_PopRange(&list_, N, start, end);
ASSERT(length_ >= N);
length_ -= N;
if (length_ < lowater_) lowater_ = length_;
}
};
// Gets and returns an object from the central cache, and, if possible,
// also adds some objects of that size class to this thread cache.
void* FetchFromCentralCache(size_t cl, size_t byte_size);
// Releases some number of items from src. Adjusts the list's max_length
// to eventually converge on num_objects_to_move(cl).
void ListTooLong(FreeList* src, size_t cl);
// Releases N items from this thread cache.
void ReleaseToCentralCache(FreeList* src, size_t cl, int N);
// Increase max_size_ by reducing unclaimed_cache_space_ or by
// reducing the max_size_ of some other thread. In both cases,
// the delta is kStealAmount.
void IncreaseCacheLimit();
// Same as above but requires Static::pageheap_lock() is held.
void IncreaseCacheLimitLocked();
// If TLS is available, we also store a copy of the per-thread object
// in a __thread variable since __thread variables are faster to read
// than pthread_getspecific(). We still need pthread_setspecific()
// because __thread variables provide no way to run cleanup code when
// a thread is destroyed.
// We also give a hint to the compiler to use the "initial exec" TLS
// model. This is faster than the default TLS model, at the cost that
// you cannot dlopen this library. (To see the difference, look at
// the CPU use of __tls_get_addr with and without this attribute.)
// Since we don't really use dlopen in google code -- and using dlopen
// on a malloc replacement is asking for trouble in any case -- that's
// a good tradeoff for us.
#ifdef HAVE_TLS
static __thread ThreadCache* threadlocal_heap_
# ifdef HAVE___ATTRIBUTE__
__attribute__ ((tls_model ("initial-exec")))
# endif
;
#endif
// Thread-specific key. Initialization here is somewhat tricky
// because some Linux startup code invokes malloc() before it
// is in a good enough state to handle pthread_keycreate().
// Therefore, we use TSD keys only after tsd_inited is set to true.
// Until then, we use a slow path to get the heap object.
static bool tsd_inited_;
static pthread_key_t heap_key_;
// Linked list of heap objects. Protected by Static::pageheap_lock.
static ThreadCache* thread_heaps_;
static int thread_heap_count_;
// A pointer to one of the objects in thread_heaps_. Represents
// the next ThreadCache from which a thread over its max_size_ should
// steal memory limit. Round-robin through all of the objects in
// thread_heaps_. Protected by Static::pageheap_lock.
static ThreadCache* next_memory_steal_;
// Overall thread cache size. Protected by Static::pageheap_lock.
static size_t overall_thread_cache_size_;
// Global per-thread cache size. Writes are protected by
// Static::pageheap_lock. Reads are done without any locking, which should be
// fine as long as size_t can be written atomically and we don't place
// invariants between this variable and other pieces of state.
static volatile size_t per_thread_cache_size_;
// Represents overall_thread_cache_size_ minus the sum of max_size_
// across all ThreadCaches. Protected by Static::pageheap_lock.
static ssize_t unclaimed_cache_space_;
// This class is laid out with the most frequently used fields
// first so that hot elements are placed on the same cache line.
size_t size_; // Combined size of data
size_t max_size_; // size_ > max_size_ --> Scavenge()
// We sample allocations, biased by the size of the allocation
Sampler sampler_; // A sampler
FreeList list_[kNumClasses]; // Array indexed by size-class
pthread_t tid_; // Which thread owns it
bool in_setspecific_; // In call to pthread_setspecific?
// Allocate a new heap. REQUIRES: Static::pageheap_lock is held.
static ThreadCache* NewHeap(pthread_t tid);
// Use only as pthread thread-specific destructor function.
static void DestroyThreadCache(void* ptr);
static void DeleteCache(ThreadCache* heap);
static void RecomputePerThreadCacheSize();
// Ensure that this class is cacheline-aligned. This is critical for
// performance, as false sharing would negate many of the benefits
// of a per-thread cache.
} CACHELINE_ALIGNED;
// Allocator for thread heaps
// This is logically part of the ThreadCache class, but MSVC, at
// least, does not like using ThreadCache as a template argument
// before the class is fully defined. So we put it outside the class.
extern PageHeapAllocator<ThreadCache> threadcache_allocator;
inline int ThreadCache::HeapsInUse() {
return threadcache_allocator.inuse();
}
inline bool ThreadCache::SampleAllocation(size_t k) {
return sampler_.SampleAllocation(k);
}
inline void* ThreadCache::Allocate(size_t size, size_t cl) {
ASSERT(size <= kMaxSize);
ASSERT(size == Static::sizemap()->ByteSizeForClass(cl));
FreeList* list = &list_[cl];
if (list->empty()) {
return FetchFromCentralCache(cl, size);
}
size_ -= size;
return list->Pop();
}
inline void ThreadCache::Deallocate(void* ptr, size_t cl) {
FreeList* list = &list_[cl];
size_ += Static::sizemap()->ByteSizeForClass(cl);
ssize_t size_headroom = max_size_ - size_ - 1;
// This catches back-to-back frees of allocs in the same size
// class. A more comprehensive (and expensive) test would be to walk
// the entire freelist. But this might be enough to find some bugs.
ASSERT(ptr != list->Next());
list->Push(ptr);
ssize_t list_headroom =
static_cast<ssize_t>(list->max_length()) - list->length();
// There are two relatively uncommon things that require further work.
// In the common case we're done, and in that case we need a single branch
// because of the bitwise-or trick that follows.
if ((list_headroom | size_headroom) < 0) {
if (list_headroom < 0) {
ListTooLong(list, cl);
}
if (size_ >= max_size_) Scavenge();
}
}
inline ThreadCache* ThreadCache::GetThreadHeap() {
#ifdef HAVE_TLS
// __thread is faster, but only when the kernel supports it
if (KernelSupportsTLS())
return threadlocal_heap_;
#endif
return reinterpret_cast<ThreadCache *>(
perftools_pthread_getspecific(heap_key_));
}
inline ThreadCache* ThreadCache::GetCache() {
ThreadCache* ptr = NULL;
if (!tsd_inited_) {
InitModule();
} else {
ptr = GetThreadHeap();
}
if (ptr == NULL) ptr = CreateCacheIfNecessary();
return ptr;
}
// In deletion paths, we do not try to create a thread-cache. This is
// because we may be in the thread destruction code and may have
// already cleaned up the cache for this thread.
inline ThreadCache* ThreadCache::GetCacheIfPresent() {
if (!tsd_inited_) return NULL;
return GetThreadHeap();
}
} // namespace tcmalloc
#endif // TCMALLOC_THREAD_CACHE_H_