diff -r 000000000000 -r 6474c204b198 xpcom/threads/HangMonitor.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/threads/HangMonitor.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,388 @@
+/* -*- 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/HangMonitor.h"
+#include "mozilla/BackgroundHangMonitor.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/ProcessedStack.h"
+#include "mozilla/Atomics.h"
+#include "nsXULAppAPI.h"
+#include "nsThreadUtils.h"
+#include "nsStackWalk.h"
+
+#ifdef MOZ_CRASHREPORTER
+#include "nsExceptionHandler.h"
+#endif
+
+#ifdef XP_WIN
+#include <windows.h>
+#endif
+
+#if defined(MOZ_ENABLE_PROFILER_SPS) && defined(MOZ_PROFILING) && defined(XP_WIN)
+  #define REPORT_CHROME_HANGS
+#endif
+
+namespace mozilla { namespace HangMonitor {
+
+/**
+ * A flag which may be set from within a debugger to disable the hang
+ * monitor.
+ */
+volatile bool gDebugDisableHangMonitor = false;
+
+const char kHangMonitorPrefName[] = "hangmonitor.timeout";
+
+const char kTelemetryPrefName[] = "toolkit.telemetry.enabled";
+
+// Monitor protects gShutdown and gTimeout, but not gTimestamp which rely on
+// being atomically set by the processor; synchronization doesn't really matter
+// in this use case.
+Monitor* gMonitor;
+
+// The timeout preference, in seconds.
+int32_t gTimeout;
+
+PRThread* gThread;
+
+// Set when shutdown begins to signal the thread to exit immediately.
+bool gShutdown;
+
+// The timestamp of the last event notification, or PR_INTERVAL_NO_WAIT if
+// we're currently not processing events.
+Atomic<PRIntervalTime> gTimestamp(PR_INTERVAL_NO_WAIT);
+
+#ifdef REPORT_CHROME_HANGS
+// Main thread ID used in reporting chrome hangs under Windows
+static HANDLE winMainThreadHandle = nullptr;
+
+// Default timeout for reporting chrome hangs to Telemetry (5 seconds)
+static const int32_t DEFAULT_CHROME_HANG_INTERVAL = 5;
+
+// Maximum number of PCs to gather from the stack
+static const int32_t MAX_CALL_STACK_PCS = 400;
+#endif
+
+// PrefChangedFunc
+void
+PrefChanged(const char*, void*)
+{
+  int32_t newval = Preferences::GetInt(kHangMonitorPrefName);
+#ifdef REPORT_CHROME_HANGS
+  // Monitor chrome hangs on the profiling branch if Telemetry enabled
+  if (newval == 0) {
+    bool telemetryEnabled = Preferences::GetBool(kTelemetryPrefName);
+    if (telemetryEnabled) {
+      newval = DEFAULT_CHROME_HANG_INTERVAL;
+    }
+  }
+#endif
+  MonitorAutoLock lock(*gMonitor);
+  if (newval != gTimeout) {
+    gTimeout = newval;
+    lock.Notify();
+  }
+}
+
+void
+Crash()
+{
+  if (gDebugDisableHangMonitor) {
+    return;
+  }
+
+#ifdef XP_WIN
+  if (::IsDebuggerPresent()) {
+    return;
+  }
+#endif
+
+#ifdef MOZ_CRASHREPORTER
+  CrashReporter::AnnotateCrashReport(NS_LITERAL_CSTRING("Hang"),
+                                     NS_LITERAL_CSTRING("1"));
+#endif
+
+  NS_RUNTIMEABORT("HangMonitor triggered");
+}
+
+#ifdef REPORT_CHROME_HANGS
+static void
+ChromeStackWalker(void *aPC, void *aSP, void *aClosure)
+{
+  MOZ_ASSERT(aClosure);
+  std::vector<uintptr_t> *stack =
+    static_cast<std::vector<uintptr_t>*>(aClosure);
+  if (stack->size() == MAX_CALL_STACK_PCS)
+    return;
+  MOZ_ASSERT(stack->size() < MAX_CALL_STACK_PCS);
+  stack->push_back(reinterpret_cast<uintptr_t>(aPC));
+}
+
+static void
+GetChromeHangReport(Telemetry::ProcessedStack &aStack,
+                    int32_t &aSystemUptime,
+                    int32_t &aFirefoxUptime)
+{
+  MOZ_ASSERT(winMainThreadHandle);
+
+  // The thread we're about to suspend might have the alloc lock
+  // so allocate ahead of time
+  std::vector<uintptr_t> rawStack;
+  rawStack.reserve(MAX_CALL_STACK_PCS);
+  DWORD ret = ::SuspendThread(winMainThreadHandle);
+  if (ret == -1)
+    return;
+  NS_StackWalk(ChromeStackWalker, /* skipFrames */ 0, /* maxFrames */ 0,
+               reinterpret_cast<void*>(&rawStack),
+               reinterpret_cast<uintptr_t>(winMainThreadHandle), nullptr);
+  ret = ::ResumeThread(winMainThreadHandle);
+  if (ret == -1)
+    return;
+  aStack = Telemetry::GetStackAndModules(rawStack);
+
+  // Record system uptime (in minutes) at the time of the hang
+  aSystemUptime = ((GetTickCount() / 1000) - (gTimeout * 2)) / 60;
+
+  // Record Firefox uptime (in minutes) at the time of the hang
+  bool error;
+  TimeStamp processCreation = TimeStamp::ProcessCreation(error);
+  if (!error) {
+    TimeDuration td = TimeStamp::Now() - processCreation;
+    aFirefoxUptime = (static_cast<int32_t>(td.ToSeconds()) - (gTimeout * 2)) / 60;
+  } else {
+    aFirefoxUptime = -1;
+  }
+}
+#endif
+
+void
+ThreadMain(void*)
+{
+  PR_SetCurrentThreadName("Hang Monitor");
+
+  MonitorAutoLock lock(*gMonitor);
+
+  // In order to avoid issues with the hang monitor incorrectly triggering
+  // during a general system stop such as sleeping, the monitor thread must
+  // run twice to trigger hang protection.
+  PRIntervalTime lastTimestamp = 0;
+  int waitCount = 0;
+
+#ifdef REPORT_CHROME_HANGS
+  Telemetry::ProcessedStack stack;
+  int32_t systemUptime = -1;
+  int32_t firefoxUptime = -1;
+#endif
+
+  while (true) {
+    if (gShutdown) {
+      return; // Exit the thread
+    }
+
+    // avoid rereading the volatile value in this loop
+    PRIntervalTime timestamp = gTimestamp;
+
+    PRIntervalTime now = PR_IntervalNow();
+
+    if (timestamp != PR_INTERVAL_NO_WAIT &&
+        now < timestamp) {
+      // 32-bit overflow, reset for another waiting period
+      timestamp = 1; // lowest legal PRInterval value
+    }
+
+    if (timestamp != PR_INTERVAL_NO_WAIT &&
+        timestamp == lastTimestamp &&
+        gTimeout > 0) {
+      ++waitCount;
+#ifdef REPORT_CHROME_HANGS
+      // Capture the chrome-hang stack + Firefox & system uptimes after
+      // the minimum hang duration has been reached (not when the hang ends)
+      if (waitCount == 2) {
+        GetChromeHangReport(stack, systemUptime, firefoxUptime);
+      }
+#else
+      // This is the crash-on-hang feature.
+      // See bug 867313 for the quirk in the waitCount comparison
+      if (waitCount >= 2) {
+        int32_t delay =
+          int32_t(PR_IntervalToSeconds(now - timestamp));
+        if (delay >= gTimeout) {
+          MonitorAutoUnlock unlock(*gMonitor);
+          Crash();
+        }
+      }
+#endif
+    }
+    else {
+#ifdef REPORT_CHROME_HANGS
+      if (waitCount >= 2) {
+        uint32_t hangDuration = PR_IntervalToSeconds(now - lastTimestamp);
+        Telemetry::RecordChromeHang(hangDuration, stack,
+                                    systemUptime, firefoxUptime);
+        stack.Clear();
+      }
+#endif
+      lastTimestamp = timestamp;
+      waitCount = 0;
+    }
+
+    PRIntervalTime timeout;
+    if (gTimeout <= 0) {
+      timeout = PR_INTERVAL_NO_TIMEOUT;
+    }
+    else {
+      timeout = PR_MillisecondsToInterval(gTimeout * 500);
+    }
+    lock.Wait(timeout);
+  }
+}
+
+void
+Startup()
+{
+  // The hang detector only runs in chrome processes. If you change this,
+  // you must also deal with the threadsafety of AnnotateCrashReport in
+  // non-chrome processes!
+  if (GeckoProcessType_Default != XRE_GetProcessType())
+    return;
+
+  MOZ_ASSERT(!gMonitor, "Hang monitor already initialized");
+  gMonitor = new Monitor("HangMonitor");
+
+  Preferences::RegisterCallback(PrefChanged, kHangMonitorPrefName, nullptr);
+  PrefChanged(nullptr, nullptr);
+
+#ifdef REPORT_CHROME_HANGS
+  Preferences::RegisterCallback(PrefChanged, kTelemetryPrefName, nullptr);
+  winMainThreadHandle =
+    OpenThread(THREAD_ALL_ACCESS, FALSE, GetCurrentThreadId());
+  if (!winMainThreadHandle)
+    return;
+#endif
+
+  // Don't actually start measuring hangs until we hit the main event loop.
+  // This potentially misses a small class of really early startup hangs,
+  // but avoids dealing with some xpcshell tests and other situations which
+  // start XPCOM but don't ever start the event loop.
+  Suspend();
+
+  gThread = PR_CreateThread(PR_USER_THREAD,
+                            ThreadMain,
+                            nullptr, PR_PRIORITY_LOW, PR_GLOBAL_THREAD,
+                            PR_JOINABLE_THREAD, 0);
+}
+
+void
+Shutdown()
+{
+  if (GeckoProcessType_Default != XRE_GetProcessType())
+    return;
+
+  MOZ_ASSERT(gMonitor, "Hang monitor not started");
+
+  { // Scope the lock we're going to delete later
+    MonitorAutoLock lock(*gMonitor);
+    gShutdown = true;
+    lock.Notify();
+  }
+
+  // thread creation could theoretically fail
+  if (gThread) {
+    PR_JoinThread(gThread);
+    gThread = nullptr;
+  }
+
+  delete gMonitor;
+  gMonitor = nullptr;
+}
+
+static bool
+IsUIMessageWaiting()
+{
+#ifndef XP_WIN
+  return false;
+#else
+  #define NS_WM_IMEFIRST WM_IME_SETCONTEXT
+  #define NS_WM_IMELAST  WM_IME_KEYUP
+  BOOL haveUIMessageWaiting = FALSE;
+  MSG msg;
+  haveUIMessageWaiting |= ::PeekMessageW(&msg, nullptr, WM_KEYFIRST, 
+                                         WM_IME_KEYLAST, PM_NOREMOVE);
+  haveUIMessageWaiting |= ::PeekMessageW(&msg, nullptr, NS_WM_IMEFIRST,
+                                         NS_WM_IMELAST, PM_NOREMOVE);
+  haveUIMessageWaiting |= ::PeekMessageW(&msg, nullptr, WM_MOUSEFIRST,
+                                         WM_MOUSELAST, PM_NOREMOVE);
+  return haveUIMessageWaiting;
+#endif
+}
+
+void
+NotifyActivity(ActivityType activityType)
+{
+  MOZ_ASSERT(NS_IsMainThread(),
+             "HangMonitor::Notify called from off the main thread.");
+
+  // Determine the activity type more specifically
+  if (activityType == kGeneralActivity) {
+    activityType = IsUIMessageWaiting() ? kActivityUIAVail : 
+                                          kActivityNoUIAVail;
+  }
+
+  // Calculate the cumulative amount of lag time since the last UI message
+  static uint32_t cumulativeUILagMS = 0;
+  switch(activityType) {
+  case kActivityNoUIAVail:
+    cumulativeUILagMS = 0;
+    break;
+  case kActivityUIAVail:
+  case kUIActivity:
+    if (gTimestamp != PR_INTERVAL_NO_WAIT) {
+      cumulativeUILagMS += PR_IntervalToMilliseconds(PR_IntervalNow() -
+                                                     gTimestamp);
+    }
+    break;
+  default:
+    break;
+  }
+
+  // This is not a locked activity because PRTimeStamp is a 32-bit quantity
+  // which can be read/written atomically, and we don't want to pay locking
+  // penalties here.
+  gTimestamp = PR_IntervalNow();
+
+  // If we have UI activity we should reset the timer and report it if it is
+  // significant enough.
+  if (activityType == kUIActivity) {
+    // The minimum amount of lag time that we should report for telemetry data.
+    // Mozilla's UI responsiveness goal is 50ms
+    static const uint32_t kUIResponsivenessThresholdMS = 50;
+    if (cumulativeUILagMS > kUIResponsivenessThresholdMS) {
+      mozilla::Telemetry::Accumulate(mozilla::Telemetry::EVENTLOOP_UI_LAG_EXP_MS,
+                                     cumulativeUILagMS);
+    }
+    cumulativeUILagMS = 0;
+  }
+
+  if (gThread && !gShutdown) {
+    mozilla::BackgroundHangMonitor().NotifyActivity();
+  }
+}
+
+void
+Suspend()
+{
+  MOZ_ASSERT(NS_IsMainThread(),
+             "HangMonitor::Suspend called from off the main thread.");
+
+  // Because gTimestamp changes this resets the wait count.
+  gTimestamp = PR_INTERVAL_NO_WAIT;
+
+  if (gThread && !gShutdown) {
+    mozilla::BackgroundHangMonitor().NotifyWait();
+  }
+}
+
+} } // namespace mozilla::HangMonitor