root/third_party/tcmalloc/vendor/src/profile-handler.cc

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DEFINITIONS

This source file includes following definitions.
  1. Init
  2. Instance
  3. timer_sharing_
  4. RegisterThread
  5. RegisterCallback
  6. UnregisterCallback
  7. Reset
  8. GetState
  9. StartTimer
  10. StopTimer
  11. IsTimerRunning
  12. EnableHandler
  13. DisableHandler
  14. IsSignalHandlerAvailable
  15. SignalHandler
  16. ProfileHandlerRegisterThread
  17. ProfileHandlerRegisterCallback
  18. ProfileHandlerUnregisterCallback
  19. ProfileHandlerReset
  20. ProfileHandlerGetState
  21. ProfileHandlerRegisterThread
  22. ProfileHandlerRegisterCallback
  23. ProfileHandlerUnregisterCallback
  24. ProfileHandlerReset
  25. ProfileHandlerGetState

// Copyright (c) 2009, 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
//         Nabeel Mian
//
// Implements management of profile timers and the corresponding signal handler.

#include "config.h"
#include "profile-handler.h"

#if !(defined(__CYGWIN__) || defined(__CYGWIN32__))

#include <stdio.h>
#include <errno.h>
#include <sys/time.h>

#include <list>
#include <string>

#include "base/dynamic_annotations.h"
#include "base/googleinit.h"
#include "base/logging.h"
#include "base/spinlock.h"
#include "maybe_threads.h"

using std::list;
using std::string;

// This structure is used by ProfileHandlerRegisterCallback and
// ProfileHandlerUnregisterCallback as a handle to a registered callback.
struct ProfileHandlerToken {
  // Sets the callback and associated arg.
  ProfileHandlerToken(ProfileHandlerCallback cb, void* cb_arg)
      : callback(cb),
        callback_arg(cb_arg) {
  }

  // Callback function to be invoked on receiving a profile timer interrupt.
  ProfileHandlerCallback callback;
  // Argument for the callback function.
  void* callback_arg;
};

// This class manages profile timers and associated signal handler. This is a
// a singleton.
class ProfileHandler {
 public:
  // Registers the current thread with the profile handler. On systems which
  // have a separate interval timer for each thread, this function starts the
  // timer for the current thread.
  //
  // The function also attempts to determine whether or not timers are shared by
  // all threads in the process.  (With LinuxThreads, and with NPTL on some
  // Linux kernel versions, each thread has separate timers.)
  //
  // Prior to determining whether timers are shared, this function will
  // unconditionally start the timer.  However, if this function determines
  // that timers are shared, then it will stop the timer if no callbacks are
  // currently registered.
  void RegisterThread();

  // Registers a callback routine to receive profile timer ticks. The returned
  // token is to be used when unregistering this callback and must not be
  // deleted by the caller. Registration of the first callback enables the
  // SIGPROF handler (or SIGALRM if using ITIMER_REAL).
  ProfileHandlerToken* RegisterCallback(ProfileHandlerCallback callback,
                                        void* callback_arg);

  // Unregisters a previously registered callback. Expects the token returned
  // by the corresponding RegisterCallback routine. Unregistering the last
  // callback disables the SIGPROF handler (or SIGALRM if using ITIMER_REAL).
  void UnregisterCallback(ProfileHandlerToken* token)
      NO_THREAD_SAFETY_ANALYSIS;

  // Unregisters all the callbacks, stops the timer if shared, disables the
  // SIGPROF (or SIGALRM) handler and clears the timer_sharing_ state.
  void Reset();

  // Gets the current state of profile handler.
  void GetState(ProfileHandlerState* state);

  // Initializes and returns the ProfileHandler singleton.
  static ProfileHandler* Instance();

 private:
  ProfileHandler();
  ~ProfileHandler();

  // Largest allowed frequency.
  static const int32 kMaxFrequency = 4000;
  // Default frequency.
  static const int32 kDefaultFrequency = 100;

  // ProfileHandler singleton.
  static ProfileHandler* instance_;

  // pthread_once_t for one time initialization of ProfileHandler singleton.
  static pthread_once_t once_;

  // Initializes the ProfileHandler singleton via GoogleOnceInit.
  static void Init();

  // The number of SIGPROF (or SIGALRM for ITIMER_REAL) interrupts received.
  int64 interrupts_ GUARDED_BY(signal_lock_);

  // SIGPROF/SIGALRM interrupt frequency, read-only after construction.
  int32 frequency_;

  // ITIMER_PROF (which uses SIGPROF), or ITIMER_REAL (which uses SIGALRM)
  int timer_type_;

  // Counts the number of callbacks registered.
  int32 callback_count_ GUARDED_BY(control_lock_);

  // Is profiling allowed at all?
  bool allowed_;

  // Whether or not the threading system provides interval timers that are
  // shared by all threads in a process.
  enum {
    // No timer initialization attempted yet.
    TIMERS_UNTOUCHED,
    // First thread has registered and set timer.
    TIMERS_ONE_SET,
    // Timers are shared by all threads.
    TIMERS_SHARED,
    // Timers are separate in each thread.
    TIMERS_SEPARATE
  } timer_sharing_ GUARDED_BY(control_lock_);

  // This lock serializes the registration of threads and protects the
  // callbacks_ list below.
  // Locking order:
  // In the context of a signal handler, acquire signal_lock_ to walk the
  // callback list. Otherwise, acquire control_lock_, disable the signal
  // handler and then acquire signal_lock_.
  SpinLock control_lock_ ACQUIRED_BEFORE(signal_lock_);
  SpinLock signal_lock_;

  // Holds the list of registered callbacks. We expect the list to be pretty
  // small. Currently, the cpu profiler (base/profiler) and thread module
  // (base/thread.h) are the only two components registering callbacks.
  // Following are the locking requirements for callbacks_:
  // For read-write access outside the SIGPROF handler:
  //  - Acquire control_lock_
  //  - Disable SIGPROF handler.
  //  - Acquire signal_lock_
  // For read-only access in the context of SIGPROF handler
  // (Read-write access is *not allowed* in the SIGPROF handler)
  //  - Acquire signal_lock_
  // For read-only access outside SIGPROF handler:
  //  - Acquire control_lock_
  typedef list<ProfileHandlerToken*> CallbackList;
  typedef CallbackList::iterator CallbackIterator;
  CallbackList callbacks_ GUARDED_BY(signal_lock_);

  // Starts the interval timer.  If the thread library shares timers between
  // threads, this function starts the shared timer. Otherwise, this will start
  // the timer in the current thread.
  void StartTimer() EXCLUSIVE_LOCKS_REQUIRED(control_lock_);

  // Stops the interval timer. If the thread library shares timers between
  // threads, this fucntion stops the shared timer. Otherwise, this will stop
  // the timer in the current thread.
  void StopTimer() EXCLUSIVE_LOCKS_REQUIRED(control_lock_);

  // Returns true if the profile interval timer is enabled in the current
  // thread.  This actually checks the kernel's interval timer setting.  (It is
  // used to detect whether timers are shared or separate.)
  bool IsTimerRunning() EXCLUSIVE_LOCKS_REQUIRED(control_lock_);

  // Sets the timer interrupt signal handler.
  void EnableHandler() EXCLUSIVE_LOCKS_REQUIRED(control_lock_);

  // Disables (ignores) the timer interrupt signal.
  void DisableHandler() EXCLUSIVE_LOCKS_REQUIRED(control_lock_);

  // Returns true if the handler is not being used by something else.
  // This checks the kernel's signal handler table.
  bool IsSignalHandlerAvailable();

  // SIGPROF/SIGALRM handler. Iterate over and call all the registered callbacks.
  static void SignalHandler(int sig, siginfo_t* sinfo, void* ucontext);

  DISALLOW_COPY_AND_ASSIGN(ProfileHandler);
};

ProfileHandler* ProfileHandler::instance_ = NULL;
pthread_once_t ProfileHandler::once_ = PTHREAD_ONCE_INIT;

const int32 ProfileHandler::kMaxFrequency;
const int32 ProfileHandler::kDefaultFrequency;

// If we are LD_PRELOAD-ed against a non-pthreads app, then
// pthread_once won't be defined.  We declare it here, for that
// case (with weak linkage) which will cause the non-definition to
// resolve to NULL.  We can then check for NULL or not in Instance.
extern "C" int pthread_once(pthread_once_t *, void (*)(void))
    ATTRIBUTE_WEAK;

void ProfileHandler::Init() {
  instance_ = new ProfileHandler();
}

ProfileHandler* ProfileHandler::Instance() {
  if (pthread_once) {
    pthread_once(&once_, Init);
  }
  if (instance_ == NULL) {
    // This will be true on systems that don't link in pthreads,
    // including on FreeBSD where pthread_once has a non-zero address
    // (but doesn't do anything) even when pthreads isn't linked in.
    Init();
    assert(instance_ != NULL);
  }
  return instance_;
}

ProfileHandler::ProfileHandler()
    : interrupts_(0),
      callback_count_(0),
      allowed_(true),
      timer_sharing_(TIMERS_UNTOUCHED) {
  SpinLockHolder cl(&control_lock_);

  timer_type_ = (getenv("CPUPROFILE_REALTIME") ? ITIMER_REAL : ITIMER_PROF);

  // Get frequency of interrupts (if specified)
  char junk;
  const char* fr = getenv("CPUPROFILE_FREQUENCY");
  if (fr != NULL && (sscanf(fr, "%u%c", &frequency_, &junk) == 1) &&
      (frequency_ > 0)) {
    // Limit to kMaxFrequency
    frequency_ = (frequency_ > kMaxFrequency) ? kMaxFrequency : frequency_;
  } else {
    frequency_ = kDefaultFrequency;
  }

  if (!allowed_) {
    return;
  }

  // If something else is using the signal handler,
  // assume it has priority over us and stop.
  if (!IsSignalHandlerAvailable()) {
    RAW_LOG(INFO, "Disabling profiler because %s handler is already in use.",
                    timer_type_ == ITIMER_REAL ? "SIGALRM" : "SIGPROF");
    allowed_ = false;
    return;
  }

  // Ignore signals until we decide to turn profiling on.  (Paranoia;
  // should already be ignored.)
  DisableHandler();
}

ProfileHandler::~ProfileHandler() {
  Reset();
}

void ProfileHandler::RegisterThread() {
  SpinLockHolder cl(&control_lock_);

  if (!allowed_) {
    return;
  }

  // We try to detect whether timers are being shared by setting a
  // timer in the first call to this function, then checking whether
  // it's set in the second call.
  //
  // Note that this detection method requires that the first two calls
  // to RegisterThread must be made from different threads.  (Subsequent
  // calls will see timer_sharing_ set to either TIMERS_SEPARATE or
  // TIMERS_SHARED, and won't try to detect the timer sharing type.)
  //
  // Also note that if timer settings were inherited across new thread
  // creation but *not* shared, this approach wouldn't work.  That's
  // not an issue for any Linux threading implementation, and should
  // not be a problem for a POSIX-compliant threads implementation.
  switch (timer_sharing_) {
    case TIMERS_UNTOUCHED:
      StartTimer();
      timer_sharing_ = TIMERS_ONE_SET;
      break;
    case TIMERS_ONE_SET:
      // If the timer is running, that means that the main thread's
      // timer setup is seen in this (second) thread -- and therefore
      // that timers are shared.
      if (IsTimerRunning()) {
        timer_sharing_ = TIMERS_SHARED;
        // If callback is already registered, we have to keep the timer
        // running.  If not, we disable the timer here.
        if (callback_count_ == 0) {
          StopTimer();
        }
      } else {
        timer_sharing_ = TIMERS_SEPARATE;
        StartTimer();
      }
      break;
    case TIMERS_SHARED:
      // Nothing needed.
      break;
    case TIMERS_SEPARATE:
      StartTimer();
      break;
  }
}

ProfileHandlerToken* ProfileHandler::RegisterCallback(
    ProfileHandlerCallback callback, void* callback_arg) {

  ProfileHandlerToken* token = new ProfileHandlerToken(callback, callback_arg);

  SpinLockHolder cl(&control_lock_);
  DisableHandler();
  {
    SpinLockHolder sl(&signal_lock_);
    callbacks_.push_back(token);
  }
  // Start the timer if timer is shared and this is a first callback.
  if ((callback_count_ == 0) && (timer_sharing_ == TIMERS_SHARED)) {
    StartTimer();
  }
  ++callback_count_;
  EnableHandler();
  return token;
}

void ProfileHandler::UnregisterCallback(ProfileHandlerToken* token) {
  SpinLockHolder cl(&control_lock_);
  for (CallbackIterator it = callbacks_.begin(); it != callbacks_.end();
       ++it) {
    if ((*it) == token) {
      RAW_CHECK(callback_count_ > 0, "Invalid callback count");
      DisableHandler();
      {
        SpinLockHolder sl(&signal_lock_);
        delete *it;
        callbacks_.erase(it);
      }
      --callback_count_;
      if (callback_count_ > 0) {
        EnableHandler();
      } else if (timer_sharing_ == TIMERS_SHARED) {
        StopTimer();
      }
      return;
    }
  }
  // Unknown token.
  RAW_LOG(FATAL, "Invalid token");
}

void ProfileHandler::Reset() {
  SpinLockHolder cl(&control_lock_);
  DisableHandler();
  {
    SpinLockHolder sl(&signal_lock_);
    CallbackIterator it = callbacks_.begin();
    while (it != callbacks_.end()) {
      CallbackIterator tmp = it;
      ++it;
      delete *tmp;
      callbacks_.erase(tmp);
    }
  }
  callback_count_ = 0;
  if (timer_sharing_ == TIMERS_SHARED) {
    StopTimer();
  }
  timer_sharing_ = TIMERS_UNTOUCHED;
}

void ProfileHandler::GetState(ProfileHandlerState* state) {
  SpinLockHolder cl(&control_lock_);
  DisableHandler();
  {
    SpinLockHolder sl(&signal_lock_);  // Protects interrupts_.
    state->interrupts = interrupts_;
  }
  if (callback_count_ > 0) {
    EnableHandler();
  }
  state->frequency = frequency_;
  state->callback_count = callback_count_;
  state->allowed = allowed_;
}

void ProfileHandler::StartTimer() {
  if (!allowed_) {
    return;
  }
  struct itimerval timer;
  timer.it_interval.tv_sec = 0;
  timer.it_interval.tv_usec = 1000000 / frequency_;
  timer.it_value = timer.it_interval;
  setitimer(timer_type_, &timer, 0);
}

void ProfileHandler::StopTimer() {
  if (!allowed_) {
    return;
  }
  struct itimerval timer;
  memset(&timer, 0, sizeof timer);
  setitimer(timer_type_, &timer, 0);
}

bool ProfileHandler::IsTimerRunning() {
  if (!allowed_) {
    return false;
  }
  struct itimerval current_timer;
  RAW_CHECK(0 == getitimer(timer_type_, &current_timer), "getitimer");
  return (current_timer.it_value.tv_sec != 0 ||
          current_timer.it_value.tv_usec != 0);
}

void ProfileHandler::EnableHandler() {
  if (!allowed_) {
    return;
  }
  struct sigaction sa;
  sa.sa_sigaction = SignalHandler;
  sa.sa_flags = SA_RESTART | SA_SIGINFO;
  sigemptyset(&sa.sa_mask);
  const int signal_number = (timer_type_ == ITIMER_PROF ? SIGPROF : SIGALRM);
  RAW_CHECK(sigaction(signal_number, &sa, NULL) == 0, "sigprof (enable)");
}

void ProfileHandler::DisableHandler() {
  if (!allowed_) {
    return;
  }
  struct sigaction sa;
  sa.sa_handler = SIG_IGN;
  sa.sa_flags = SA_RESTART;
  sigemptyset(&sa.sa_mask);
  const int signal_number = (timer_type_ == ITIMER_PROF ? SIGPROF : SIGALRM);
  RAW_CHECK(sigaction(signal_number, &sa, NULL) == 0, "sigprof (disable)");
}

bool ProfileHandler::IsSignalHandlerAvailable() {
  struct sigaction sa;
  const int signal_number = (timer_type_ == ITIMER_PROF ? SIGPROF : SIGALRM);
  RAW_CHECK(sigaction(signal_number, NULL, &sa) == 0, "is-signal-handler avail");

  // We only take over the handler if the current one is unset.
  // It must be SIG_IGN or SIG_DFL, not some other function.
  // SIG_IGN must be allowed because when profiling is allowed but
  // not actively in use, this code keeps the handler set to SIG_IGN.
  // That setting will be inherited across fork+exec.  In order for
  // any child to be able to use profiling, SIG_IGN must be treated
  // as available.
  return sa.sa_handler == SIG_IGN || sa.sa_handler == SIG_DFL;
}

void ProfileHandler::SignalHandler(int sig, siginfo_t* sinfo, void* ucontext) {
  int saved_errno = errno;
  // At this moment, instance_ must be initialized because the handler is
  // enabled in RegisterThread or RegisterCallback only after
  // ProfileHandler::Instance runs.
  ProfileHandler* instance = ANNOTATE_UNPROTECTED_READ(instance_);
  RAW_CHECK(instance != NULL, "ProfileHandler is not initialized");
  {
    SpinLockHolder sl(&instance->signal_lock_);
    ++instance->interrupts_;
    for (CallbackIterator it = instance->callbacks_.begin();
         it != instance->callbacks_.end();
         ++it) {
      (*it)->callback(sig, sinfo, ucontext, (*it)->callback_arg);
    }
  }
  errno = saved_errno;
}

// This module initializer registers the main thread, so it must be
// executed in the context of the main thread.
REGISTER_MODULE_INITIALIZER(profile_main, ProfileHandlerRegisterThread());

extern "C" void ProfileHandlerRegisterThread() {
  ProfileHandler::Instance()->RegisterThread();
}

extern "C" ProfileHandlerToken* ProfileHandlerRegisterCallback(
    ProfileHandlerCallback callback, void* callback_arg) {
  return ProfileHandler::Instance()->RegisterCallback(callback, callback_arg);
}

extern "C" void ProfileHandlerUnregisterCallback(ProfileHandlerToken* token) {
  ProfileHandler::Instance()->UnregisterCallback(token);
}

extern "C" void ProfileHandlerReset() {
  return ProfileHandler::Instance()->Reset();
}

extern "C" void ProfileHandlerGetState(ProfileHandlerState* state) {
  ProfileHandler::Instance()->GetState(state);
}

#else  // OS_CYGWIN

// ITIMER_PROF doesn't work under cygwin.  ITIMER_REAL is available, but doesn't
// work as well for profiling, and also interferes with alarm().  Because of
// these issues, unless a specific need is identified, profiler support is
// disabled under Cygwin.
extern "C" void ProfileHandlerRegisterThread() {
}

extern "C" ProfileHandlerToken* ProfileHandlerRegisterCallback(
    ProfileHandlerCallback callback, void* callback_arg) {
  return NULL;
}

extern "C" void ProfileHandlerUnregisterCallback(ProfileHandlerToken* token) {
}

extern "C" void ProfileHandlerReset() {
}

extern "C" void ProfileHandlerGetState(ProfileHandlerState* state) {
}

#endif  // OS_CYGWIN

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