1 files changed, 734 insertions, 0 deletions
diff --git a/xpcom/threads/BackgroundHangMonitor.cpp b/xpcom/threads/BackgroundHangMonitor.cpp
new file mode 100644
index 000000000..ac65d9f37
--- /dev/null
+++ b/xpcom/threads/BackgroundHangMonitor.cpp
@@ -0,0 +1,734 @@
+/* -*- 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