gecko/xpcom/threads/HangMonitor.cpp

/* -*- 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/Monitor.h"
#include "mozilla/Preferences.h"
#include "mozilla/Telemetry.h"
#include "mozilla/ProcessedStack.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";

#ifdef MOZ_TELEMETRY_ON_BY_DEFAULT
const char kTelemetryPrefName[] = "toolkit.telemetry.enabledPreRelease";
#else
const char kTelemetryPrefName[] = "toolkit.telemetry.enabled";
#endif

// 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.
volatile PRIntervalTime gTimestamp = PR_INTERVAL_NO_WAIT;

#ifdef REPORT_CHROME_HANGS
// Main thread ID used in reporting chrome hangs under Windows
static HANDLE winMainThreadHandle = NULL;

// 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
int
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();
  }

  return 0;
}

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)
{
  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);
}
#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;
#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;
      if (waitCount >= 2) {
#ifdef REPORT_CHROME_HANGS
        GetChromeHangReport(stack);
#else
        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);
        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, NULL);
  PrefChanged(NULL, NULL);

#ifdef REPORT_CHROME_HANGS
  Preferences::RegisterCallback(PrefChanged, kTelemetryPrefName, NULL);
  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,
                            NULL, 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 = NULL;
  }

  delete gMonitor;
  gMonitor = NULL;
}

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, NULL, WM_KEYFIRST, 
                                         WM_IME_KEYLAST, PM_NOREMOVE);
  haveUIMessageWaiting |= ::PeekMessageW(&msg, NULL, NS_WM_IMEFIRST,
                                         NS_WM_IMELAST, PM_NOREMOVE);
  haveUIMessageWaiting |= ::PeekMessageW(&msg, NULL, 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;
  }
}

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;
}

} } // namespace mozilla::HangMonitor