The Tor Browser: xpcom/threads/BackgroundHangMonitor.cpp@b8a032363ba2 (annotated)

xpcom/threads/BackgroundHangMonitor.cpp@b8a032363ba2 (annotated)

xpcom/threads/BackgroundHangMonitor.cpp

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* 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/StaticPtr.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/ThreadHangStats.h"
 #include "mozilla/ThreadLocal.h"
 #ifdef MOZ_NUWA_PROCESS
 #include "ipc/Nuwa.h"
 #endif
 #include "prinrval.h"
 #include "prthread.h"
 #include "ThreadStackHelper.h"
 #include <algorithm>
 namespace mozilla {
 /**
  * BackgroundHangManager is the global object that
  * manages all instances of BackgroundHangThread.
  */
 class BackgroundHangManager
 {
 private:
   // Background hang monitor thread function
   static void MonitorThread(void* aData)
   {
     PR_SetCurrentThreadName("BgHangManager");
 #ifdef MOZ_NUWA_PROCESS
     if (IsNuwaProcess()) {
       NS_ASSERTION(NuwaMarkCurrentThread != nullptr,
                    "NuwaMarkCurrentThread is undefined!");
       NuwaMarkCurrentThread(nullptr, nullptr);
     }
 #endif
     /* 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_INLINE_DECL_THREADSAFE_REFCOUNTING(BackgroundHangManager)
   static StaticRefPtr<BackgroundHangManager> sInstance;
   // 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();
   ~BackgroundHangManager();
 };
 /**
  * BackgroundHangThread is a per-thread object that is used
  * by all instances of BackgroundHangMonitor to monitor hangs.
  */
 class BackgroundHangThread : public LinkedListElement<BackgroundHangThread>
 {
 private:
   static ThreadLocal<BackgroundHangThread*> sTlsKey;
   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;
 public:
   NS_INLINE_DECL_REFCOUNTING(BackgroundHangThread)
   static BackgroundHangThread* FindThread();
   static void Startup()
   {
     /* We can tolerate init() failing.
        The if block turns off warn_unused_result. */
     if (!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;
   // Platform-specific helper to get hang stacks
   ThreadStackHelper mStackHelper;
   // Stack of current hang
   Telemetry::HangHistogram::Stack mHangStack;
   // Statistics for telemetry
   Telemetry::ThreadHangStats mStats;
   BackgroundHangThread(const char* aName,
                        uint32_t aTimeoutMs,
                        uint32_t aMaxTimeoutMs);
   // Report a hang; aManager->mLock IS locked
   void ReportHang(PRIntervalTime aHangTime);
   // Report a permanent hang; aManager->mLock IS locked
   void ReportPermaHang();
   // Called by BackgroundHangMonitor::NotifyActivity
   void NotifyActivity();
   // Called by BackgroundHangMonitor::NotifyWait
   void NotifyWait()
   {
     NotifyActivity();
     mWaiting = true;
   }
 };
 StaticRefPtr<BackgroundHangManager> BackgroundHangManager::sInstance;
 ThreadLocal<BackgroundHangThread*> BackgroundHangThread::sTlsKey;
 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;
         }
       } 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);
       /* 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)
   : 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)
   , mStats(aName)
 {
   if (sTlsKey.initialized()) {
     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 (sTlsKey.initialized()) {
     sTlsKey.set(nullptr);
   }
   // Move our copy of ThreadHangStats to Telemetry storage
   Telemetry::RecordThreadHangStats(mStats);
 }
 void
 BackgroundHangThread::ReportHang(PRIntervalTime aHangTime)
 {
   // Recovered from a hang; called on the monitor thread
   // mManager->mLock IS locked
   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);
       return;
     }
   }
   // Add new histogram
   newHistogram.Add(aHangTime);
   mStats.mHangs.append(Move(newHistogram));
 }
 void
 BackgroundHangThread::ReportPermaHang()
 {
   // Permanently hanged; called on the monitor thread
   // mManager->mLock IS locked
   // TODO: Add more detailed analysis for perma-hangs
   ReportHang(mMaxTimeout);
 }
 MOZ_ALWAYS_INLINE void
 BackgroundHangThread::NotifyActivity()
 {
   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 (sTlsKey.initialized()) {
     // 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) {
       return thread;
     }
   }
 #endif
   // Current thread is not initialized
   return nullptr;
 }
 void
 BackgroundHangMonitor::Startup()
 {
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   MOZ_ASSERT(!BackgroundHangManager::sInstance, "Already initialized");
   ThreadStackHelper::Startup();
   BackgroundHangThread::Startup();
   BackgroundHangManager::sInstance = new BackgroundHangManager();
 #endif
 }
 void
 BackgroundHangMonitor::Shutdown()
 {
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   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();
 #endif
 }
 BackgroundHangMonitor::BackgroundHangMonitor(const char* aName,
                                              uint32_t aTimeoutMs,
                                              uint32_t aMaxTimeoutMs)
   : mThread(BackgroundHangThread::FindThread())
 {
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   if (!mThread) {
     mThread = new BackgroundHangThread(aName, aTimeoutMs, aMaxTimeoutMs);
   }
 #endif
 }
 BackgroundHangMonitor::BackgroundHangMonitor()
   : mThread(BackgroundHangThread::FindThread())
 {
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   MOZ_ASSERT(mThread, "Thread not initialized for hang monitoring");
 #endif
 }
 BackgroundHangMonitor::~BackgroundHangMonitor()
 {
 }
 void
 BackgroundHangMonitor::NotifyActivity()
 {
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   mThread->NotifyActivity();
 #endif
 }
 void
 BackgroundHangMonitor::NotifyWait()
 {
 #ifdef MOZ_ENABLE_BACKGROUND_HANG_MONITOR
   mThread->NotifyWait();
 #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->mHangThreads.getFirst())
 {
 }
 Telemetry::ThreadHangStats*
 BackgroundHangMonitor::ThreadHangStatsIterator::GetNext()
 {
   if (!mThread) {
     return nullptr;
   }
   Telemetry::ThreadHangStats* stats = &mThread->mStats;
   mThread = mThread->getNext();
   return stats;
 }
 } // namespace mozilla

The Tor Browser / annotate

xpcom/threads/BackgroundHangMonitor.cpp@b8a032363ba2 (annotated)

xpcom/threads/BackgroundHangMonitor.cpp