| // -*- Mode: C++; c-basic-offset: 2; indent-tabs-mode: nil -*- |
| // Copyright (c) 2009, Google Inc. |
| // All rights reserved. |
| // |
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| // modification, are permitted provided that the following conditions are |
| // met: |
| // |
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| // 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 |
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| // 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_, ¤t_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 |