/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ #include "mozilla/ArrayUtils.h" #include "mozilla/BackgroundHangMonitor.h" #include "mozilla/LinkedList.h" #include "mozilla/Monitor.h" #include "mozilla/Move.h" #include "mozilla/Preferences.h" #include "mozilla/StaticPtr.h" #include "mozilla/Telemetry.h" #include "mozilla/ThreadHangStats.h" #include "mozilla/ThreadLocal.h" #include "prinrval.h" #include "prthread.h" #include "ThreadStackHelper.h" #include "nsIObserverService.h" #include "nsIObserver.h" #include "mozilla/Services.h" #include "nsXULAppAPI.h" #include <algorithm> // Activate BHR only for one every BHR_BETA_MOD users. // This is now 100% of Beta population for the Beta 45/46 e10s A/B trials // It can be scaled back again in the future #define BHR_BETA_MOD 1; // Maximum depth of the call stack in the reported thread hangs. This value represents // the 99.9th percentile of the thread hangs stack depths reported by Telemetry. static const size_t kMaxThreadHangStackDepth = 30; // An utility comparator function used by std::unique to collapse "(* script)" entries in // a vector representing a call stack. bool StackScriptEntriesCollapser(const char* aStackEntry, const char *aAnotherStackEntry) { return !strcmp(aStackEntry, aAnotherStackEntry) && (!strcmp(aStackEntry, "(chrome script)") || !strcmp(aStackEntry, "(content script)")); } namespace mozilla { /** * BackgroundHangManager is the global object that * manages all instances of BackgroundHangThread. */ class BackgroundHangManager : public nsIObserver { private: // Background hang monitor thread function static void MonitorThread(void* aData) { PR_SetCurrentThreadName("BgHangManager"); /* We do not hold a reference to BackgroundHangManager here because the monitor thread only exists as long as the BackgroundHangManager instance exists. We stop the monitor thread in the BackgroundHangManager destructor, and we can only get to the destructor if we don't hold a reference here. */ static_cast<BackgroundHangManager*>(aData)->RunMonitorThread(); } // Hang monitor thread PRThread* mHangMonitorThread; // Stop hang monitoring bool mShutdown; BackgroundHangManager(const BackgroundHangManager&); BackgroundHangManager& operator=(const BackgroundHangManager&); void RunMonitorThread(); public: NS_DECL_THREADSAFE_ISUPPORTS NS_DECL_NSIOBSERVER static StaticRefPtr<BackgroundHangManager> sInstance; static bool sDisabled; // Lock for access to members of this class Monitor mLock; // Current time as seen by hang monitors PRIntervalTime mIntervalNow; // List of BackgroundHangThread instances associated with each thread LinkedList<BackgroundHangThread> mHangThreads; void Shutdown() { MonitorAutoLock autoLock(mLock); mShutdown = true; autoLock.Notify(); } void Wakeup() { // PR_CreateThread could have failed earlier if (mHangMonitorThread) { // Use PR_Interrupt to avoid potentially taking a lock PR_Interrupt(mHangMonitorThread); } } BackgroundHangManager(); private: virtual ~BackgroundHangManager(); }; NS_IMPL_ISUPPORTS(BackgroundHangManager, nsIObserver) NS_IMETHODIMP BackgroundHangManager::Observe(nsISupports* aSubject, const char* aTopic, const char16_t* aData) { NS_ENSURE_TRUE(!strcmp(aTopic, "profile-after-change"), NS_ERROR_UNEXPECTED); BackgroundHangMonitor::DisableOnBeta(); nsCOMPtr<nsIObserverService> observerService = mozilla::services::GetObserverService(); MOZ_ASSERT(observerService); observerService->RemoveObserver(this, "profile-after-change"); return NS_OK; } /** * BackgroundHangThread is a per-thread object that is used * by all instances of BackgroundHangMonitor to monitor hangs. */ class BackgroundHangThread : public LinkedListElement<BackgroundHangThread> { private: static MOZ_THREAD_LOCAL(BackgroundHangThread*) sTlsKey; static bool sTlsKeyInitialized; BackgroundHangThread(const BackgroundHangThread&); BackgroundHangThread& operator=(const BackgroundHangThread&); ~BackgroundHangThread(); /* Keep a reference to the manager, so we can keep going even after BackgroundHangManager::Shutdown is called. */ const RefPtr<BackgroundHangManager> mManager; // Unique thread ID for identification const PRThread* mThreadID; void Update(); public: NS_INLINE_DECL_REFCOUNTING(BackgroundHangThread) /** * Returns the BackgroundHangThread associated with the * running thread. Note that this will not find private * BackgroundHangThread threads. * * @return BackgroundHangThread*, or nullptr if no thread * is found. */ static BackgroundHangThread* FindThread(); static void Startup() { /* We can tolerate init() failing. */ sTlsKeyInitialized = sTlsKey.init(); } // Hang timeout in ticks const PRIntervalTime mTimeout; // PermaHang timeout in ticks const PRIntervalTime mMaxTimeout; // Time at last activity PRIntervalTime mInterval; // Time when a hang started PRIntervalTime mHangStart; // Is the thread in a hang bool mHanging; // Is the thread in a waiting state bool mWaiting; // Is the thread dedicated to a single BackgroundHangMonitor BackgroundHangMonitor::ThreadType mThreadType; // Platform-specific helper to get hang stacks ThreadStackHelper mStackHelper; // Stack of current hang Telemetry::HangStack mHangStack; // Statistics for telemetry Telemetry::ThreadHangStats mStats; // Annotations for the current hang UniquePtr<HangMonitor::HangAnnotations> mAnnotations; // Annotators registered for this thread HangMonitor::Observer::Annotators mAnnotators; BackgroundHangThread(const char* aName, uint32_t aTimeoutMs, uint32_t aMaxTimeoutMs, BackgroundHangMonitor::ThreadType aThreadType = BackgroundHangMonitor::THREAD_SHARED); // Report a hang; aManager->mLock IS locked Telemetry::HangHistogram& ReportHang(PRIntervalTime aHangTime); // Report a permanent hang; aManager->mLock IS locked void ReportPermaHang(); // Called by BackgroundHangMonitor::NotifyActivity void NotifyActivity() { MonitorAutoLock autoLock(mManager->mLock); Update(); } // Called by BackgroundHangMonitor::NotifyWait void NotifyWait() { MonitorAutoLock autoLock(mManager->mLock); if (mWaiting) { return; } Update(); mWaiting = true; } // Returns true if this thread is (or might be) shared between other // BackgroundHangMonitors for the monitored thread. bool IsShared() { return mThreadType == BackgroundHangMonitor::THREAD_SHARED; } }; StaticRefPtr<BackgroundHangManager> BackgroundHangManager::sInstance; bool BackgroundHangManager::sDisabled = false; MOZ_THREAD_LOCAL(BackgroundHangThread*) BackgroundHangThread::sTlsKey; bool BackgroundHangThread::sTlsKeyInitialized; BackgroundHangManager::BackgroundHangManager() : mShutdown(false) , mLock("BackgroundHangManager") , mIntervalNow(0) { // Lock so we don't race against the new monitor thread MonitorAutoLock autoLock(mLock); mHangMonitorThread = PR_CreateThread( PR_USER_THREAD, MonitorThread, this, PR_PRIORITY_LOW, PR_GLOBAL_THREAD, PR_JOINABLE_THREAD, 0); MOZ_ASSERT(mHangMonitorThread, "Failed to create monitor thread"); } BackgroundHangManager::~BackgroundHangManager() { MOZ_ASSERT(mShutdown, "Destruction without Shutdown call"); MOZ_ASSERT(mHangThreads.isEmpty(), "Destruction with outstanding monitors"); MOZ_ASSERT(mHangMonitorThread, "No monitor thread"); // PR_CreateThread could have failed above due to resource limitation if (mHangMonitorThread) { // The monitor thread can only live as long as the instance lives PR_JoinThread(mHangMonitorThread); } } void BackgroundHangManager::RunMonitorThread() { // Keep us locked except when waiting MonitorAutoLock autoLock(mLock); /* mIntervalNow is updated at various intervals determined by waitTime. However, if an update latency is too long (due to CPU scheduling, system sleep, etc.), we don't update mIntervalNow at all. This is done so that long latencies in our timing are not detected as hangs. systemTime is used to track PR_IntervalNow() and determine our latency. */ PRIntervalTime systemTime = PR_IntervalNow(); // Default values for the first iteration of thread loop PRIntervalTime waitTime = PR_INTERVAL_NO_WAIT; PRIntervalTime recheckTimeout = PR_INTERVAL_NO_WAIT; while (!mShutdown) { PR_ClearInterrupt(); nsresult rv = autoLock.Wait(waitTime); PRIntervalTime newTime = PR_IntervalNow(); PRIntervalTime systemInterval = newTime - systemTime; systemTime = newTime; /* waitTime is a quarter of the shortest timeout value; If our timing latency is low enough (less than half the shortest timeout value), we can update mIntervalNow. */ if (MOZ_LIKELY(waitTime != PR_INTERVAL_NO_TIMEOUT && systemInterval < 2 * waitTime)) { mIntervalNow += systemInterval; } /* If it's before the next recheck timeout, and our wait did not get interrupted (either through Notify or PR_Interrupt), we can keep the current waitTime and skip iterating through hang monitors. */ if (MOZ_LIKELY(systemInterval < recheckTimeout && systemInterval >= waitTime && rv == NS_OK)) { recheckTimeout -= systemInterval; continue; } /* We are in one of the following scenarios, - Hang or permahang recheck timeout - Thread added/removed - Thread wait or hang ended In all cases, we want to go through our list of hang monitors and update waitTime and recheckTimeout. */ waitTime = PR_INTERVAL_NO_TIMEOUT; recheckTimeout = PR_INTERVAL_NO_TIMEOUT; // Locally hold mIntervalNow PRIntervalTime intervalNow = mIntervalNow; // iterate through hang monitors for (BackgroundHangThread* currentThread = mHangThreads.getFirst(); currentThread; currentThread = currentThread->getNext()) { if (currentThread->mWaiting) { // Thread is waiting, not hanging continue; } PRIntervalTime interval = currentThread->mInterval; PRIntervalTime hangTime = intervalNow - interval; if (MOZ_UNLIKELY(hangTime >= currentThread->mMaxTimeout)) { // A permahang started // Skip subsequent iterations and tolerate a race on mWaiting here currentThread->mWaiting = true; currentThread->mHanging = false; currentThread->ReportPermaHang(); continue; } if (MOZ_LIKELY(!currentThread->mHanging)) { if (MOZ_UNLIKELY(hangTime >= currentThread->mTimeout)) { // A hang started currentThread->mStackHelper.GetStack(currentThread->mHangStack); currentThread->mHangStart = interval; currentThread->mHanging = true; currentThread->mAnnotations = currentThread->mAnnotators.GatherAnnotations(); } } else { if (MOZ_LIKELY(interval != currentThread->mHangStart)) { // A hang ended currentThread->ReportHang(intervalNow - currentThread->mHangStart); currentThread->mHanging = false; } } /* If we are hanging, the next time we check for hang status is when the hang turns into a permahang. If we're not hanging, the next recheck timeout is when we may be entering a hang. */ PRIntervalTime nextRecheck; if (currentThread->mHanging) { nextRecheck = currentThread->mMaxTimeout; } else { nextRecheck = currentThread->mTimeout; } recheckTimeout = std::min(recheckTimeout, nextRecheck - hangTime); if (currentThread->mTimeout != PR_INTERVAL_NO_TIMEOUT) { /* We wait for a quarter of the shortest timeout value to give mIntervalNow enough granularity. */ waitTime = std::min(waitTime, currentThread->mTimeout / 4); } } } /* We are shutting down now. Wait for all outstanding monitors to unregister. */ while (!mHangThreads.isEmpty()) { autoLock.Wait(PR_INTERVAL_NO_TIMEOUT); } } BackgroundHangThread::BackgroundHangThread(const char* aName, uint32_t aTimeoutMs, uint32_t aMaxTimeoutMs, BackgroundHangMonitor::ThreadType aThreadType) : mManager(BackgroundHangManager::sInstance) , mThreadID(PR_GetCurrentThread()) , mTimeout(aTimeoutMs == BackgroundHangMonitor::kNoTimeout ? PR_INTERVAL_NO_TIMEOUT : PR_MillisecondsToInterval(aTimeoutMs)) , mMaxTimeout(aMaxTimeoutMs == BackgroundHangMonitor::kNoTimeout ? PR_INTERVAL_NO_TIMEOUT : PR_MillisecondsToInterval(aMaxTimeoutMs)) , mInterval(mManager->mIntervalNow) , mHangStart(mInterval) , mHanging(false) , mWaiting(true) , mThreadType(aThreadType) , mStats(aName) { if (sTlsKeyInitialized && IsShared()) { sTlsKey.set(this); } // Lock here because LinkedList is not thread-safe MonitorAutoLock autoLock(mManager->mLock); // Add to thread list mManager->mHangThreads.insertBack(this); // Wake up monitor thread to process new thread autoLock.Notify(); } BackgroundHangThread::~BackgroundHangThread() { // Lock here because LinkedList is not thread-safe MonitorAutoLock autoLock(mManager->mLock); // Remove from thread list remove(); // Wake up monitor thread to process removed thread autoLock.Notify(); // We no longer have a thread if (sTlsKeyInitialized && IsShared()) { sTlsKey.set(nullptr); } // Move our copy of ThreadHangStats to Telemetry storage Telemetry::RecordThreadHangStats(mStats); } Telemetry::HangHistogram& BackgroundHangThread::ReportHang(PRIntervalTime aHangTime) { // Recovered from a hang; called on the monitor thread // mManager->mLock IS locked // Remove unwanted "js::RunScript" frame from the stack for (size_t i = 0; i < mHangStack.length(); ) { const char** f = mHangStack.begin() + i; if (!mHangStack.IsInBuffer(*f) && !strcmp(*f, "js::RunScript")) { mHangStack.erase(f); } else { i++; } } // Collapse duplicated "(chrome script)" and "(content script)" entries in the stack. auto it = std::unique(mHangStack.begin(), mHangStack.end(), StackScriptEntriesCollapser); mHangStack.erase(it, mHangStack.end()); // Limit the depth of the reported stack if greater than our limit. Only keep its // last entries, since the most recent frames are at the end of the vector. if (mHangStack.length() > kMaxThreadHangStackDepth) { const int elementsToRemove = mHangStack.length() - kMaxThreadHangStackDepth; // Replace the oldest frame with a known label so that we can tell this stack // was limited. mHangStack[0] = "(reduced stack)"; mHangStack.erase(mHangStack.begin() + 1, mHangStack.begin() + elementsToRemove); } Telemetry::HangHistogram newHistogram(Move(mHangStack)); for (Telemetry::HangHistogram* oldHistogram = mStats.mHangs.begin(); oldHistogram != mStats.mHangs.end(); oldHistogram++) { if (newHistogram == *oldHistogram) { // New histogram matches old one oldHistogram->Add(aHangTime, Move(mAnnotations)); return *oldHistogram; } } // Add new histogram newHistogram.Add(aHangTime, Move(mAnnotations)); if (!mStats.mHangs.append(Move(newHistogram))) { MOZ_CRASH(); } return mStats.mHangs.back(); } void BackgroundHangThread::ReportPermaHang() { // Permanently hanged; called on the monitor thread // mManager->mLock IS locked Telemetry::HangHistogram& hang = ReportHang(mMaxTimeout); Telemetry::HangStack& stack = hang.GetNativeStack(); if (stack.empty()) { mStackHelper.GetNativeStack(stack); } } MOZ_ALWAYS_INLINE void BackgroundHangThread::Update() { PRIntervalTime intervalNow = mManager->mIntervalNow; if (mWaiting) { mInterval = intervalNow; mWaiting = false; /* We have to wake up the manager thread because when all threads are waiting, the manager thread waits indefinitely as well. */ mManager->Wakeup(); } else { PRIntervalTime duration = intervalNow - mInterval; mStats.mActivity.Add(duration); if (MOZ_UNLIKELY(duration >= mTimeout)) { /* Wake up the manager thread to tell it that a hang ended */ mManager->Wakeup(); } mInterval = intervalNow; } } BackgroundHangThread* BackgroundHangThread::FindThread() { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR if (BackgroundHangManager::sInstance == nullptr) { MOZ_ASSERT(BackgroundHangManager::sDisabled, "BackgroundHandleManager is not initialized"); return nullptr; } if (sTlsKeyInitialized) { // Use TLS if available return sTlsKey.get(); } // If TLS is unavailable, we can search through the thread list RefPtr<BackgroundHangManager> manager(BackgroundHangManager::sInstance); MOZ_ASSERT(manager, "Creating BackgroundHangMonitor after shutdown"); PRThread* threadID = PR_GetCurrentThread(); // Lock thread list for traversal MonitorAutoLock autoLock(manager->mLock); for (BackgroundHangThread* thread = manager->mHangThreads.getFirst(); thread; thread = thread->getNext()) { if (thread->mThreadID == threadID && thread->IsShared()) { return thread; } } #endif // Current thread is not initialized return nullptr; } bool BackgroundHangMonitor::ShouldDisableOnBeta(const nsCString &clientID) { MOZ_ASSERT(clientID.Length() == 36, "clientID is invalid"); const char *suffix = clientID.get() + clientID.Length() - 4; return strtol(suffix, NULL, 16) % BHR_BETA_MOD; } bool BackgroundHangMonitor::IsDisabled() { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR return BackgroundHangManager::sDisabled; #else return true; #endif } bool BackgroundHangMonitor::DisableOnBeta() { nsAdoptingCString clientID = Preferences::GetCString("toolkit.telemetry.cachedClientID"); bool telemetryEnabled = Preferences::GetBool("toolkit.telemetry.enabled"); if (!telemetryEnabled || !clientID || BackgroundHangMonitor::ShouldDisableOnBeta(clientID)) { if (XRE_IsParentProcess()) { BackgroundHangMonitor::Shutdown(); } else { BackgroundHangManager::sDisabled = true; } return true; } return false; } void BackgroundHangMonitor::Startup() { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR MOZ_ASSERT(!BackgroundHangManager::sInstance, "Already initialized"); if (!strcmp(NS_STRINGIFY(MOZ_UPDATE_CHANNEL), "beta")) { if (XRE_IsParentProcess()) { // cached ClientID hasn't been read yet ThreadStackHelper::Startup(); BackgroundHangThread::Startup(); BackgroundHangManager::sInstance = new BackgroundHangManager(); nsCOMPtr<nsIObserverService> observerService = mozilla::services::GetObserverService(); MOZ_ASSERT(observerService); observerService->AddObserver(BackgroundHangManager::sInstance, "profile-after-change", false); return; } else if(DisableOnBeta()){ return; } } ThreadStackHelper::Startup(); BackgroundHangThread::Startup(); BackgroundHangManager::sInstance = new BackgroundHangManager(); #endif } void BackgroundHangMonitor::Shutdown() { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR if (BackgroundHangManager::sDisabled) { MOZ_ASSERT(!BackgroundHangManager::sInstance, "Initialized"); return; } MOZ_ASSERT(BackgroundHangManager::sInstance, "Not initialized"); /* Scope our lock inside Shutdown() because the sInstance object can be destroyed as soon as we set sInstance to nullptr below, and we don't want to hold the lock when it's being destroyed. */ BackgroundHangManager::sInstance->Shutdown(); BackgroundHangManager::sInstance = nullptr; ThreadStackHelper::Shutdown(); BackgroundHangManager::sDisabled = true; #endif } BackgroundHangMonitor::BackgroundHangMonitor(const char* aName, uint32_t aTimeoutMs, uint32_t aMaxTimeoutMs, ThreadType aThreadType) : mThread(aThreadType == THREAD_SHARED ? BackgroundHangThread::FindThread() : nullptr) { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR if (!BackgroundHangManager::sDisabled && !mThread) { mThread = new BackgroundHangThread(aName, aTimeoutMs, aMaxTimeoutMs, aThreadType); } #endif } BackgroundHangMonitor::BackgroundHangMonitor() : mThread(BackgroundHangThread::FindThread()) { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR if (BackgroundHangManager::sDisabled) { return; } #endif } BackgroundHangMonitor::~BackgroundHangMonitor() { } void BackgroundHangMonitor::NotifyActivity() { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR if (mThread == nullptr) { MOZ_ASSERT(BackgroundHangManager::sDisabled, "This thread is not initialized for hang monitoring"); return; } if (Telemetry::CanRecordExtended()) { mThread->NotifyActivity(); } #endif } void BackgroundHangMonitor::NotifyWait() { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR if (mThread == nullptr) { MOZ_ASSERT(BackgroundHangManager::sDisabled, "This thread is not initialized for hang monitoring"); return; } if (Telemetry::CanRecordExtended()) { mThread->NotifyWait(); } #endif } bool BackgroundHangMonitor::RegisterAnnotator(HangMonitor::Annotator& aAnnotator) { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR BackgroundHangThread* thisThread = BackgroundHangThread::FindThread(); if (!thisThread) { return false; } return thisThread->mAnnotators.Register(aAnnotator); #else return false; #endif } bool BackgroundHangMonitor::UnregisterAnnotator(HangMonitor::Annotator& aAnnotator) { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR BackgroundHangThread* thisThread = BackgroundHangThread::FindThread(); if (!thisThread) { return false; } return thisThread->mAnnotators.Unregister(aAnnotator); #else return false; #endif } /* Because we are iterating through the BackgroundHangThread linked list, we need to take a lock. Using MonitorAutoLock as a base class makes sure all of that is taken care of for us. */ BackgroundHangMonitor::ThreadHangStatsIterator::ThreadHangStatsIterator() : MonitorAutoLock(BackgroundHangManager::sInstance->mLock) , mThread(BackgroundHangManager::sInstance ? BackgroundHangManager::sInstance->mHangThreads.getFirst() : nullptr) { #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR MOZ_ASSERT(BackgroundHangManager::sInstance || BackgroundHangManager::sDisabled, "Inconsistent state"); #endif } Telemetry::ThreadHangStats* BackgroundHangMonitor::ThreadHangStatsIterator::GetNext() { if (!mThread) { return nullptr; } Telemetry::ThreadHangStats* stats = &mThread->mStats; mThread = mThread->getNext(); return stats; } } // namespace mozilla