Revert of C++ readability review (patchset #10 id:180001 of...

Revert of C++ readability review (patchset #10 id:180001 of https://codereview.chromium.org/706993003/)

Reason for revert:
It looks like this broke tests the following tests on Linux Chromium OS:
AlarmTimerTest.OneShotTimerConcurrentResetAndTimerFired
AlarmTimerTest.RepeatingTimerConcurrentResetAndTimerFired

Example output:
AlarmTimerTest.OneShotTimerConcurrentResetAndTimerFired (run #1):
[ RUN      ] AlarmTimerTest.OneShotTimerConcurrentResetAndTimerFired
[11334:11334:0406/201742:404219967:INFO:alarm_timer_chromeos.cc(166)] CLOCK_REALTIME_ALARM not supported on this system: Invalid argument
[11334:11334:0406/201742:404230154:FATAL:timer.cc(116)] Check failed: !user_task_.is_null().

AlarmTimerTest.RepeatingTimerConcurrentResetAndTimerFired (run #1):
[ RUN      ] AlarmTimerTest.RepeatingTimerConcurrentResetAndTimerFired
[11382:11382:0406/201748:411022458:INFO:alarm_timer_chromeos.cc(166)] CLOCK_REALTIME_ALARM not supported on this system: Invalid argument
../../components/timers/alarm_timer_unittest.cc:469: Failure
Value of: did_run
  Actual: true
Expected: false

Example build:
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/996

Original issue's description:
> C++ readability review
>
> BUG=b/18275087
>
> Committed: https://crrev.com/05e4d854dca737cfb43cd967cd72d024f6b1625b
> Cr-Commit-Position: refs/heads/master@{#324004}

TBR=derat@chromium.org,gromer@google.com,zea@chromium.org,chirantan@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=b/18275087

Review URL: https://codereview.chromium.org/1058693003

Cr-Commit-Position: refs/heads/master@{#324009}

components/gcm_driver/gcm_driver_desktop.cc

@@ -25,7 +25,7 @@
 #include "net/url_request/url_request_context_getter.h"
 
 #if defined(OS_CHROMEOS)
-#include "components/timers/alarm_timer_chromeos.h"
+#include "components/timers/alarm_timer.h"
 #endif
 
 namespace gcm {
@@ -344,7 +344,7 @@ void GCMDriverDesktop::IOWorker::WakeFromSuspendForHeartbeat(bool wake) {
 
   scoped_ptr<base::Timer> timer;
   if (wake)
-    timer.reset(new timers::SimpleAlarmTimer());
+    timer.reset(new timers::AlarmTimer(true, false));
   else
     timer.reset(new base::Timer(true, false));
 

components/timers.gypi

@@ -15,8 +15,10 @@
         '../base/base.gyp:base',
       ],
       'sources': [
-        'timers/alarm_timer_chromeos.cc',
-        'timers/alarm_timer_chromeos.h',
+        'timers/alarm_timer.cc',
+        'timers/alarm_timer.h',
+        'timers/rtc_alarm.cc',
+        'timers/rtc_alarm.h',
       ],
     },
   ],

components/timers/BUILD.gn

@@ -4,8 +4,10 @@
 
 static_library("timers") {
   sources = [
-    "alarm_timer_chromeos.cc",
-    "alarm_timer_chromeos.h",
+    "alarm_timer.cc",
+    "alarm_timer.h",
+    "rtc_alarm.cc",
+    "rtc_alarm.h",
   ]
 
   deps = [

components/timers/alarm_timer.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/timers/alarm_timer.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/files/file_util.h"
+#include "base/logging.h"
+#include "base/pending_task.h"
+#include "components/timers/rtc_alarm.h"
+
+namespace timers {
+
+AlarmTimer::AlarmTimer(bool retain_user_task, bool is_repeating)
+    : base::Timer(retain_user_task, is_repeating),
+      delegate_(new RtcAlarm()),
+      can_wake_from_suspend_(false),
+      origin_message_loop_(NULL),
+      weak_factory_(this) {
+  can_wake_from_suspend_ = delegate_->Init(weak_factory_.GetWeakPtr());
+}
+
+AlarmTimer::AlarmTimer(const tracked_objects::Location& posted_from,
+                       base::TimeDelta delay,
+                       const base::Closure& user_task,
+                       bool is_repeating)
+    : base::Timer(posted_from, delay, user_task, is_repeating),
+      delegate_(new RtcAlarm()),
+      can_wake_from_suspend_(false),
+      origin_message_loop_(NULL),
+      weak_factory_(this) {
+  can_wake_from_suspend_ = delegate_->Init(weak_factory_.GetWeakPtr());
+}
+
+AlarmTimer::~AlarmTimer() {
+  Stop();
+}
+
+void AlarmTimer::OnTimerFired() {
+  if (!base::Timer::IsRunning())
+    return;
+
+  DCHECK(pending_task_.get());
+
+  // Take ownership of the pending user task, which is going to be cleared by
+  // the Stop() or Reset() functions below.
+  scoped_ptr<base::PendingTask> pending_user_task(pending_task_.Pass());
+
+  // Re-schedule or stop the timer as requested.
+  if (base::Timer::is_repeating())
+    Reset();
+  else
+    Stop();
+
+  // Now run the user task.
+  base::MessageLoop::current()->task_annotator()->RunTask(
+      "AlarmTimer::Reset", "AlarmTimer::OnTimerFired", *pending_user_task);
+}
+
+void AlarmTimer::Stop() {
+  if (!can_wake_from_suspend_) {
+    base::Timer::Stop();
+    return;
+  }
+
+  // Clear the running flag, stop the delegate, and delete the pending task.
+  base::Timer::set_is_running(false);
+  delegate_->Stop();
+  pending_task_.reset();
+
+  // Stop is called when the AlarmTimer is destroyed so we need to remove
+  // ourselves as a MessageLoop::DestructionObserver to prevent a segfault
+  // later.
+  if (origin_message_loop_) {
+    origin_message_loop_->RemoveDestructionObserver(this);
+    origin_message_loop_ = NULL;
+  }
+
+  if (!base::Timer::retain_user_task())
+    base::Timer::set_user_task(base::Closure());
+}
+
+void AlarmTimer::Reset() {
+  if (!can_wake_from_suspend_) {
+    base::Timer::Reset();
+    return;
+  }
+
+  DCHECK(!base::Timer::user_task().is_null());
+  DCHECK(!origin_message_loop_ ||
+         origin_message_loop_->task_runner()->RunsTasksOnCurrentThread());
+
+  // Make sure that the timer will stop if the underlying message loop is
+  // destroyed.
+  if (!origin_message_loop_) {
+    origin_message_loop_ = base::MessageLoop::current();
+    origin_message_loop_->AddDestructionObserver(this);
+  }
+
+  // Set up the pending task.
+  if (base::Timer::GetCurrentDelay() > base::TimeDelta::FromMicroseconds(0)) {
+    base::Timer::set_desired_run_time(
+        base::TimeTicks::Now() + base::Timer::GetCurrentDelay());
+    pending_task_.reset(new base::PendingTask(base::Timer::posted_from(),
+                                              base::Timer::user_task(),
+                                              base::Timer::desired_run_time(),
+                                              true  /* nestable */));
+  } else {
+    base::Timer::set_desired_run_time(base::TimeTicks());
+    pending_task_.reset(new base::PendingTask(base::Timer::posted_from(),
+                                              base::Timer::user_task()));
+  }
+  base::MessageLoop::current()->task_annotator()->DidQueueTask(
+      "AlarmTimer::Reset", *pending_task_);
+
+  // Now start up the timer.
+  delegate_->Reset(base::Timer::GetCurrentDelay());
+  base::Timer::set_is_running(true);
+}
+
+void AlarmTimer::WillDestroyCurrentMessageLoop() {
+  Stop();
+}
+
+}  // namespace timers

components/timers/alarm_timer_chromeos.h → components/timers/alarm_timer.h

@@ -2,18 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_
-#define COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_
+#ifndef COMPONENTS_TIMER_ALARM_TIMER_H_
+#define COMPONENTS_TIMER_ALARM_TIMER_H_
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 
 namespace base {
-class MessageLoop;
 struct PendingTask;
 }
 
@@ -24,45 +24,61 @@ namespace timers {
 // Currently, this feature is only available on Chrome OS systems running linux
 // version 3.11 or higher.  On all other platforms, the AlarmTimer behaves
 // exactly the same way as a regular Timer.
-class AlarmTimer : public base::Timer {
+class AlarmTimer : public base::Timer,
+                   public base::MessageLoop::DestructionObserver {
  public:
-  ~AlarmTimer() override;
-
-  bool can_wake_from_suspend() const { return can_wake_from_suspend_; }
+  // The delegate is responsible for managing the system level details for
+  // actually setting up and monitoring a timer that is capable of waking the
+  // system from suspend.  This class is reference counted because it may need
+  // to outlive the timer in order to clean up after itself.
+  class Delegate : public base::RefCountedThreadSafe<Delegate> {
+   public:
+    // Initializes the timer.  Should return true iff the system has timers that
+    // can wake it up from suspend.  Will only be called once.
+    virtual bool Init(base::WeakPtr<AlarmTimer> timer) = 0;
 
-  // Sets a hook that will be called when the timer fires and a task has been
-  // queued on |origin_message_loop_|.  Used by tests to wait until a task is
-  // pending in the MessageLoop.
-  void SetTimerFiredCallbackForTest(base::Closure test_callback);
+    // Stops the currently running timer.  It should be safe to call this more
+    // than once.
+    virtual void Stop() = 0;
 
-  // Timer overrides.
-  void Stop() override;
-  void Reset() override;
+    // Resets the timer to fire after |delay| has passed.  Cancels any
+    // pre-existing delay.
+    virtual void Reset(base::TimeDelta delay) = 0;
 
    protected:
-  // The constructors for this class are protected because consumers should
-  // instantiate one of the specialized sub-classes defined below instead.
+    virtual ~Delegate() {}
+
+   private:
+    friend class base::RefCountedThreadSafe<Delegate>;
+  };
+
   AlarmTimer(bool retain_user_task, bool is_repeating);
+
   AlarmTimer(const tracked_objects::Location& posted_from,
              base::TimeDelta delay,
              const base::Closure& user_task,
              bool is_repeating);
 
- private:
-  // Common initialization that must be performed by both constructors.  This
-  // really should live in a delegated constructor but the way base::Timer's
-  // constructors are written makes it really hard to do so.
-  void Init();
+  ~AlarmTimer() override;
 
-  // Will be called by the delegate to indicate that the timer has fired and
+  bool can_wake_from_suspend() const { return can_wake_from_suspend_; }
+
+  // Must be called by the delegate to indicate that the timer has fired and
   // that the user task should be run.
   void OnTimerFired();
 
-  // Called when |origin_message_loop_| will be destroyed.
-  void WillDestroyCurrentMessageLoop();
+  // Timer overrides.
+  void Stop() override;
+  void Reset() override;
+
+  // MessageLoop::DestructionObserver overrides.
+  void WillDestroyCurrentMessageLoop() override;
+
+ private:
+  // Initializes the timer with the appropriate delegate.
+  void Init();
 
   // Delegate that will manage actually setting the timer.
-  class Delegate;
   scoped_refptr<Delegate> delegate_;
 
   // Keeps track of the user task we want to run.  A new one is constructed
@@ -79,68 +95,11 @@ class AlarmTimer : public base::Timer {
   // destruction of that message loop.
   base::MessageLoop* origin_message_loop_;
 
-  // Observes |origin_message_loop_| and informs this class if it will be
-  // destroyed.
-  class MessageLoopObserver;
-  scoped_ptr<MessageLoopObserver> message_loop_observer_;
-
   base::WeakPtrFactory<AlarmTimer> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AlarmTimer);
 };
 
-// As its name suggests, a OneShotAlarmTimer runs a given task once.  It does
-// not remember the task that was given to it after it has fired and does not
-// repeat.  Useful for fire-and-forget tasks.
-class OneShotAlarmTimer : public AlarmTimer {
- public:
-  // Constructs a basic OneShotAlarmTimer.  An AlarmTimer constructed this way
-  // requires that Start() is called before Reset() is called.
-  OneShotAlarmTimer();
-  ~OneShotAlarmTimer() override;
-};
-
-// A RepeatingAlarmTimer takes a task and delay and repeatedly runs the task
-// using the specified delay as an interval between the runs until it is
-// explicitly stopped.  It remembers both the task and the delay it was given
-// after it fires.
-class RepeatingAlarmTimer : public AlarmTimer {
- public:
-  // Constructs a basic RepeatingAlarmTimer.  An AlarmTimer constructed this way
-  // requires that Start() is called before Reset() is called.
-  RepeatingAlarmTimer();
-
-  // Constructs a RepeatingAlarmTimer with pre-populated parameters but does not
-  // start it.  Useful if |user_task| or |delay| are not going to change.
-  // Reset() can be called immediately after constructing an AlarmTimer in this
-  // way.
-  RepeatingAlarmTimer(const tracked_objects::Location& posted_from,
-                      base::TimeDelta delay,
-                      const base::Closure& user_task);
-
-  ~RepeatingAlarmTimer() override;
-};
-
-// A SimpleAlarmTimer only fires once but remembers the task that it was given
-// even after it has fired.  Useful if you want to run the same task multiple
-// times but not at a regular interval.
-class SimpleAlarmTimer : public AlarmTimer {
- public:
-  // Constructs a basic SimpleAlarmTimer.  An AlarmTimer constructed this way
-  // requires that Start() is called before Reset() is called.
-  SimpleAlarmTimer();
-
-  // Constructs a SimpleAlarmTimer with pre-populated parameters but does not
-  // start it.  Useful if |user_task| or |delay| are not going to change.
-  // Reset() can be called immediately after constructing an AlarmTimer in this
-  // way.
-  SimpleAlarmTimer(const tracked_objects::Location& posted_from,
-                   base::TimeDelta delay,
-                   const base::Closure& user_task);
-
-  ~SimpleAlarmTimer() override;
-};
-
 }  // namespace timers
 
-#endif  // COMPONENTS_TIMERS_ALARM_TIMER_CHROMEOS_H_
+#endif  // COMPONENTS_TIMER_ALARM_TIMER_H_

components/timers/alarm_timer_chromeos.cc

-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "components/timers/alarm_timer_chromeos.h"
-
-#include <sys/timerfd.h>
-
-#include "base/bind.h"
-#include "base/bind_helpers.h"
-#include "base/files/file_util.h"
-#include "base/lazy_instance.h"
-#include "base/logging.h"
-#include "base/macros.h"
-#include "base/message_loop/message_loop.h"
-#include "base/message_loop/message_loop_proxy.h"
-#include "base/pending_task.h"
-#include "base/threading/thread.h"
-
-namespace timers {
-namespace {
-// This class represents the IO thread that the AlarmTimer::Delegate may use for
-// watching file descriptors if it gets called from a thread that does not have
-// a MessageLoopForIO.  It is a lazy global instance because it may not always
-// be necessary.
-class RtcAlarmIOThread : public base::Thread {
- public:
-  RtcAlarmIOThread() : Thread("RTC Alarm IO Thread") {
-    CHECK(
-        StartWithOptions(base::Thread::Options(base::MessageLoop::TYPE_IO, 0)));
-  }
-  ~RtcAlarmIOThread() override { Stop(); }
-};
-
-base::LazyInstance<RtcAlarmIOThread> g_io_thread = LAZY_INSTANCE_INITIALIZER;
-
-}  // namespace
-
-// Watches a MessageLoop and runs a callback if that MessageLoop will be
-// destroyed.
-class AlarmTimer::MessageLoopObserver
-    : public base::MessageLoop::DestructionObserver {
- public:
-  // Constructs a MessageLoopObserver that will observe |message_loop| and will
-  // call |on_will_be_destroyed_callback| when |message_loop| is about to be
-  // destroyed.
-  MessageLoopObserver(base::MessageLoop* message_loop,
-                      base::Closure on_will_be_destroyed_callback)
-      : message_loop_(message_loop),
-        on_will_be_destroyed_callback_(on_will_be_destroyed_callback) {
-    DCHECK(message_loop_);
-    message_loop_->AddDestructionObserver(this);
-  }
-
-  ~MessageLoopObserver() override {
-    // If |message_loop_| was destroyed, then this class will have already
-    // unregistered itself.  Doing it again will trigger a warning.
-    if (message_loop_)
-      message_loop_->RemoveDestructionObserver(this);
-  }
-
-  // base::MessageLoop::DestructionObserver override.
-  void WillDestroyCurrentMessageLoop() override {
-    message_loop_->RemoveDestructionObserver(this);
-    message_loop_ = NULL;
-
-    on_will_be_destroyed_callback_.Run();
-  }
-
- private:
-  // The MessageLoop that this class should watch.  Is a weak pointer.
-  base::MessageLoop* message_loop_;
-
-  // The callback to run when |message_loop_| will be destroyed.
-  base::Closure on_will_be_destroyed_callback_;
-
-  DISALLOW_COPY_AND_ASSIGN(MessageLoopObserver);
-};
-
-// This class manages a Real Time Clock (RTC) alarm, a feature that is available
-// from linux version 3.11 onwards.  It creates a file descriptor for the RTC
-// alarm timer and then watches that file descriptor to see when it can be read
-// without blocking, indicating that the timer has fired.
-//
-// A major problem for this class is that watching file descriptors is only
-// available on a MessageLoopForIO but there is no guarantee the timer is going
-// to be created on one.  To get around this, the timer has a dedicated thread
-// with a MessageLoopForIO that posts tasks back to the thread that started the
-// timer.
-class AlarmTimer::Delegate
-    : public base::RefCountedThreadSafe<AlarmTimer::Delegate>,
-      public base::MessageLoopForIO::Watcher {
- public:
-  // Construct a Delegate for the AlarmTimer.  It should be safe to call
-  // |on_timer_fired_callback| multiple times.
-  explicit Delegate(base::Closure on_timer_fired_callback);
-
-  // Returns true if the system timer managed by this delegate is capable of
-  // waking the system from suspend.
-  bool CanWakeFromSuspend();
-
-  // Resets the timer to fire after |delay| has passed.  Cancels any
-  // pre-existing delay.
-  void Reset(base::TimeDelta delay);
-
-  // Stops the currently running timer.  It should be safe to call this even if
-  // the timer is not running.
-  void Stop();
-
-  // Sets a hook that will be called when the timer fires and a task has been
-  // queued on |origin_message_loop_|.  Used by tests to wait until a task is
-  // pending in the MessageLoop.
-  void SetTimerFiredCallbackForTest(base::Closure test_callback);
-
-  // base::MessageLoopForIO::Watcher overrides.
-  void OnFileCanReadWithoutBlocking(int fd) override;
-  void OnFileCanWriteWithoutBlocking(int fd) override;
-
- private:
-  friend class base::RefCountedThreadSafe<Delegate>;
-  ~Delegate() override;
-
-  // Actually performs the system calls to set up the timer.  This must be
-  // called on a MessageLoopForIO.
-  void ResetImpl(base::TimeDelta delay, int reset_sequence_number);
-
-  // Callback that is run when the timer fires.  Must be run on
-  // |origin_message_loop_|.
-  void OnTimerFired(int reset_sequence_number);
-
-  // File descriptor associated with the alarm timer.
-  int alarm_fd_;
-
-  // Message loop which initially started the timer.
-  scoped_refptr<base::MessageLoopProxy> origin_message_loop_;
-
-  // Callback that should be run when the timer fires.
-  base::Closure on_timer_fired_callback_;
-
-  // Hook used by tests to be notified when the timer has fired and a task has
-  // been queued in the MessageLoop.
-  base::Closure on_timer_fired_callback_for_test_;
-
-  // Manages watching file descriptors.
-  scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> fd_watcher_;
-
-  // The sequence numbers of the last Reset() call handled respectively on
-  // |origin_message_loop_| and on the MessageLoopForIO used for watching the
-  // timer file descriptor.  Note that these can be the same MessageLoop.
-  // OnTimerFired() runs |on_timer_fired_callback_| only if the sequence number
-  // it receives from the MessageLoopForIO matches
-  // |origin_reset_sequence_number_|.
-  int origin_reset_sequence_number_;
-  int io_reset_sequence_number_;
-
-  DISALLOW_COPY_AND_ASSIGN(Delegate);
-};
-
-AlarmTimer::Delegate::Delegate(base::Closure on_timer_fired_callback)
-    : alarm_fd_(timerfd_create(CLOCK_REALTIME_ALARM, 0)),
-      on_timer_fired_callback_(on_timer_fired_callback),
-      origin_reset_sequence_number_(0),
-      io_reset_sequence_number_(0) {
-  // The call to timerfd_create above may fail.  This is the only indication
-  // that CLOCK_REALTIME_ALARM is not supported on this system.
-  DPLOG_IF(INFO, (alarm_fd_ == -1))
-      << "CLOCK_REALTIME_ALARM not supported on this system";
-}
-
-AlarmTimer::Delegate::~Delegate() {
-  if (alarm_fd_ != -1)
-    close(alarm_fd_);
-}
-
-bool AlarmTimer::Delegate::CanWakeFromSuspend() {
-  return alarm_fd_ != -1;
-}
-
-void AlarmTimer::Delegate::Reset(base::TimeDelta delay) {
-  // Get a proxy for the current message loop.  When the timer fires, we will
-  // post tasks to this proxy to let the parent timer know.
-  origin_message_loop_ = base::MessageLoopProxy::current();
-
-  // Increment the sequence number.  Used to invalidate any events that have
-  // been queued but not yet run since the last time Reset() was called.
-  origin_reset_sequence_number_++;
-
-  // Calling timerfd_settime with a zero delay actually clears the timer so if
-  // the user has requested a zero delay timer, we need to handle it
-  // differently.  We queue the task here but we still go ahead and call
-  // timerfd_settime with the zero delay anyway to cancel any previous delay
-  // that might have been programmed.
-  if (delay <= base::TimeDelta::FromMicroseconds(0)) {
-    // The timerfd_settime documentation is vague on what happens when it is
-    // passed a negative delay.  We can sidestep the issue by ensuring that
-    // the delay is 0.
-    delay = base::TimeDelta::FromMicroseconds(0);
-    origin_message_loop_->PostTask(
-        FROM_HERE,
-        base::Bind(&Delegate::OnTimerFired, scoped_refptr<Delegate>(this),
-                   origin_reset_sequence_number_));
-  }
-
-  // Run ResetImpl() on a MessageLoopForIO.
-  if (base::MessageLoopForIO::IsCurrent()) {
-    ResetImpl(delay, origin_reset_sequence_number_);
-  } else {
-    g_io_thread.Pointer()->task_runner()->PostTask(
-        FROM_HERE,
-        base::Bind(&Delegate::ResetImpl, scoped_refptr<Delegate>(this), delay,
-                   origin_reset_sequence_number_));
-  }
-}
-
-void AlarmTimer::Delegate::Stop() {
-  // Stop the RTC from a MessageLoopForIO.
-  if (!base::MessageLoopForIO::IsCurrent()) {
-    g_io_thread.Pointer()->task_runner()->PostTask(
-        FROM_HERE, base::Bind(&Delegate::Stop, scoped_refptr<Delegate>(this)));
-    return;
-  }
-
-  // Stop watching for events.
-  fd_watcher_.reset();
-
-  // Now clear the timer.
-  DCHECK_NE(alarm_fd_, -1);
-  itimerspec blank_time = {};
-  if (timerfd_settime(alarm_fd_, 0, &blank_time, NULL) < 0)
-    PLOG(ERROR) << "Unable to clear alarm time.  Timer may still fire.";
-}
-
-void AlarmTimer::Delegate::OnFileCanReadWithoutBlocking(int fd) {
-  DCHECK_EQ(alarm_fd_, fd);
-
-  // Read from the fd to ack the event.
-  char val[sizeof(uint64_t)];
-  if (!base::ReadFromFD(alarm_fd_, val, sizeof(uint64_t)))
-    PLOG(DFATAL) << "Unable to read from timer file descriptor.";
-
-  // Make sure that the parent timer is informed on the proper message loop.
-  if (origin_message_loop_->RunsTasksOnCurrentThread()) {
-    OnTimerFired(io_reset_sequence_number_);
-  } else {
-    origin_message_loop_->PostTask(
-        FROM_HERE,
-        base::Bind(&Delegate::OnTimerFired, scoped_refptr<Delegate>(this),
-                   io_reset_sequence_number_));
-  }
-}
-
-void AlarmTimer::Delegate::OnFileCanWriteWithoutBlocking(int fd) {
-  NOTREACHED();
-}
-
-void AlarmTimer::Delegate::SetTimerFiredCallbackForTest(
-    base::Closure test_callback) {
-  on_timer_fired_callback_for_test_ = test_callback;
-}
-
-void AlarmTimer::Delegate::ResetImpl(base::TimeDelta delay,
-                                     int reset_sequence_number) {
-  DCHECK(base::MessageLoopForIO::IsCurrent());
-  DCHECK_NE(alarm_fd_, -1);
-
-  // Store the sequence number in the IO thread variable.  When the timer
-  // fires, we will bind this value to the OnTimerFired callback to ensure
-  // that we do the right thing if the timer gets reset.
-  io_reset_sequence_number_ = reset_sequence_number;
-
-  // If we were already watching the fd, this will stop watching it.
-  fd_watcher_.reset(new base::MessageLoopForIO::FileDescriptorWatcher);
-
-  // Start watching the fd to see when the timer fires.
-  if (!base::MessageLoopForIO::current()->WatchFileDescriptor(
-          alarm_fd_, false, base::MessageLoopForIO::WATCH_READ,
-          fd_watcher_.get(), this)) {
-    LOG(ERROR) << "Error while attempting to watch file descriptor for RTC "
-               << "alarm.  Timer will not fire.";
-  }
-
-  // Actually set the timer.  This will also clear the pre-existing timer, if
-  // any.
-  itimerspec alarm_time = {};
-  alarm_time.it_value.tv_sec = delay.InSeconds();
-  alarm_time.it_value.tv_nsec =
-      (delay.InMicroseconds() % base::Time::kMicrosecondsPerSecond) *
-      base::Time::kNanosecondsPerMicrosecond;
-  if (timerfd_settime(alarm_fd_, 0, &alarm_time, NULL) < 0)
-    PLOG(ERROR) << "Error while setting alarm time.  Timer will not fire";
-}
-
-void AlarmTimer::Delegate::OnTimerFired(int reset_sequence_number) {
-  DCHECK(origin_message_loop_->RunsTasksOnCurrentThread());
-
-  // If a test wants to be notified when this function is about to run, then
-  // re-queue this task in the MessageLoop and run the test's callback.
-  if (!on_timer_fired_callback_for_test_.is_null()) {
-    origin_message_loop_->PostTask(
-        FROM_HERE,
-        base::Bind(&Delegate::OnTimerFired, scoped_refptr<Delegate>(this),
-                   reset_sequence_number));
-
-    on_timer_fired_callback_for_test_.Run();
-    on_timer_fired_callback_for_test_.Reset();
-    return;
-  }
-
-  // Check to make sure that the timer was not reset in the time between when
-  // this task was queued to run and now.  If it was reset, then don't do
-  // anything.
-  if (reset_sequence_number != origin_reset_sequence_number_)
-    return;
-
-  on_timer_fired_callback_.Run();
-}
-
-AlarmTimer::AlarmTimer(bool retain_user_task, bool is_repeating)
-    : base::Timer(retain_user_task, is_repeating),
-      can_wake_from_suspend_(false),
-      origin_message_loop_(NULL),
-      weak_factory_(this) {
-  Init();
-}
-
-AlarmTimer::AlarmTimer(const tracked_objects::Location& posted_from,
-                       base::TimeDelta delay,
-                       const base::Closure& user_task,
-                       bool is_repeating)
-    : base::Timer(posted_from, delay, user_task, is_repeating),
-      can_wake_from_suspend_(false),
-      origin_message_loop_(NULL),
-      weak_factory_(this) {
-  Init();
-}
-
-AlarmTimer::~AlarmTimer() {
-  Stop();
-}
-
-void AlarmTimer::SetTimerFiredCallbackForTest(base::Closure test_callback) {
-  delegate_->SetTimerFiredCallbackForTest(test_callback);
-}
-
-void AlarmTimer::Init() {
-  delegate_ = make_scoped_refptr(new AlarmTimer::Delegate(
-      base::Bind(&AlarmTimer::OnTimerFired, weak_factory_.GetWeakPtr())));
-  can_wake_from_suspend_ = delegate_->CanWakeFromSuspend();
-}
-
-void AlarmTimer::Stop() {
-  if (!can_wake_from_suspend_) {
-    base::Timer::Stop();
-    return;
-  }
-
-  // Clear the running flag, stop the delegate, and delete the pending task.
-  base::Timer::set_is_running(false);
-  delegate_->Stop();
-  pending_task_.reset();
-
-  // Stop watching |origin_message_loop_|.
-  origin_message_loop_ = NULL;
-  message_loop_observer_.reset();
-
-  if (!base::Timer::retain_user_task())
-    base::Timer::set_user_task(base::Closure());
-}
-
-void AlarmTimer::Reset() {
-  if (!can_wake_from_suspend_) {
-    base::Timer::Reset();
-    return;
-  }
-
-  DCHECK(!base::Timer::user_task().is_null());
-  DCHECK(!origin_message_loop_ ||
-         origin_message_loop_->task_runner()->RunsTasksOnCurrentThread());
-
-  // Make sure that the timer will stop if the underlying message loop is
-  // destroyed.
-  if (!origin_message_loop_) {
-    origin_message_loop_ = base::MessageLoop::current();
-    message_loop_observer_.reset(new MessageLoopObserver(
-        origin_message_loop_,
-        base::Bind(&AlarmTimer::WillDestroyCurrentMessageLoop,
-                   weak_factory_.GetWeakPtr())));
-  }
-
-  // Set up the pending task.
-  if (base::Timer::GetCurrentDelay() > base::TimeDelta::FromMicroseconds(0)) {
-    base::Timer::set_desired_run_time(base::TimeTicks::Now() +
-                                      base::Timer::GetCurrentDelay());
-    pending_task_.reset(new base::PendingTask(
-        base::Timer::posted_from(), base::Timer::user_task(),
-        base::Timer::desired_run_time(), true /* nestable */));
-  } else {
-    base::Timer::set_desired_run_time(base::TimeTicks());
-    pending_task_.reset(new base::PendingTask(base::Timer::posted_from(),
-                                              base::Timer::user_task()));
-  }
-  base::MessageLoop::current()->task_annotator()->DidQueueTask(
-      "AlarmTimer::Reset", *pending_task_);
-
-  // Now start up the timer.
-  delegate_->Reset(base::Timer::GetCurrentDelay());
-  base::Timer::set_is_running(true);
-}
-
-void AlarmTimer::WillDestroyCurrentMessageLoop() {
-  Stop();
-}
-
-void AlarmTimer::OnTimerFired() {
-  if (!base::Timer::IsRunning())
-    return;
-
-  DCHECK(pending_task_.get());
-
-  // Take ownership of the pending user task, which is going to be cleared by
-  // the Stop() or Reset() functions below.
-  scoped_ptr<base::PendingTask> pending_user_task(pending_task_.Pass());
-
-  // Re-schedule or stop the timer as requested.
-  if (base::Timer::is_repeating())
-    Reset();
-  else
-    Stop();
-
-  // Now run the user task.
-  base::MessageLoop::current()->task_annotator()->RunTask(
-      "AlarmTimer::Reset", "AlarmTimer::OnTimerFired", *pending_user_task);
-}
-
-OneShotAlarmTimer::OneShotAlarmTimer() : AlarmTimer(false, false) {
-}
-
-OneShotAlarmTimer::~OneShotAlarmTimer() {
-}
-
-RepeatingAlarmTimer::RepeatingAlarmTimer() : AlarmTimer(true, true) {
-}
-
-RepeatingAlarmTimer::RepeatingAlarmTimer(
-    const tracked_objects::Location& posted_from,
-    base::TimeDelta delay,
-    const base::Closure& user_task)
-    : AlarmTimer(posted_from, delay, user_task, true) {
-}
-
-RepeatingAlarmTimer::~RepeatingAlarmTimer() {
-}
-
-SimpleAlarmTimer::SimpleAlarmTimer() : AlarmTimer(true, false) {
-}
-
-SimpleAlarmTimer::SimpleAlarmTimer(const tracked_objects::Location& posted_from,
-                                   base::TimeDelta delay,
-                                   const base::Closure& user_task)
-    : AlarmTimer(posted_from, delay, user_task, false) {
-}
-
-SimpleAlarmTimer::~SimpleAlarmTimer() {
-}
-
-}  // namespace timers

components/timers/alarm_timer_unittest.cc

@@ -9,7 +9,7 @@
 #include "base/run_loop.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/time.h"
-#include "components/timers/alarm_timer_chromeos.h"
+#include "components/timers/alarm_timer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 // Most of these tests have been lifted right out of timer_unittest.cc with only
@@ -39,9 +39,12 @@ class OneShotAlarmTimerTester {
   OneShotAlarmTimerTester(bool* did_run, base::TimeDelta delay)
       : did_run_(did_run),
         delay_(delay),
-        timer_(new timers::OneShotAlarmTimer()) {}
+        timer_(new timers::AlarmTimer(false, false)) {
+  }
   void Start() {
-    timer_->Start(FROM_HERE, delay_, base::Bind(&OneShotAlarmTimerTester::Run,
+    timer_->Start(FROM_HERE,
+                  delay_,
+                  base::Bind(&OneShotAlarmTimerTester::Run,
                              base::Unretained(this)));
   }
 
@@ -55,7 +58,7 @@ class OneShotAlarmTimerTester {
 
   bool* did_run_;
   const base::TimeDelta delay_;
-  scoped_ptr<timers::OneShotAlarmTimer> timer_;
+  scoped_ptr<timers::AlarmTimer> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(OneShotAlarmTimerTester);
 };
@@ -65,9 +68,11 @@ class OneShotSelfDeletingAlarmTimerTester {
   OneShotSelfDeletingAlarmTimerTester(bool* did_run, base::TimeDelta delay)
       : did_run_(did_run),
         delay_(delay),
-        timer_(new timers::OneShotAlarmTimer()) {}
+        timer_(new timers::AlarmTimer(false, false)) {
+  }
   void Start() {
-    timer_->Start(FROM_HERE, delay_,
+    timer_->Start(FROM_HERE,
+                  delay_,
                   base::Bind(&OneShotSelfDeletingAlarmTimerTester::Run,
                              base::Unretained(this)));
   }
@@ -83,7 +88,7 @@ class OneShotSelfDeletingAlarmTimerTester {
 
   bool* did_run_;
   const base::TimeDelta delay_;
-  scoped_ptr<timers::OneShotAlarmTimer> timer_;
+  scoped_ptr<timers::AlarmTimer> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(OneShotSelfDeletingAlarmTimerTester);
 };
@@ -94,9 +99,12 @@ class RepeatingAlarmTimerTester {
       : did_run_(did_run),
         delay_(delay),
         counter_(10),
-        timer_(new timers::RepeatingAlarmTimer()) {}
+        timer_(new timers::AlarmTimer(true, true)) {
+  }
   void Start() {
-    timer_->Start(FROM_HERE, delay_, base::Bind(&RepeatingAlarmTimerTester::Run,
+    timer_->Start(FROM_HERE,
+                  delay_,
+                  base::Bind(&RepeatingAlarmTimerTester::Run,
                              base::Unretained(this)));
   }
 
@@ -114,20 +122,13 @@ class RepeatingAlarmTimerTester {
   bool* did_run_;
   const base::TimeDelta delay_;
   int counter_;
-  scoped_ptr<timers::RepeatingAlarmTimer> timer_;
+  scoped_ptr<timers::AlarmTimer> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(RepeatingAlarmTimerTester);
 };
 
-}  // namespace
-
-//-----------------------------------------------------------------------------
-// Each test is run against each type of MessageLoop.  That way we are sure
-// that timers work properly in all configurations.
-
-TEST(AlarmTimerTest, OneShotAlarmTimer) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_OneShotAlarmTimer(base::MessageLoop::Type message_loop_type) {
+  base::MessageLoop loop(message_loop_type);
 
   bool did_run = false;
   OneShotAlarmTimerTester f(&did_run, kTenMilliseconds);
@@ -136,16 +137,15 @@ TEST(AlarmTimerTest, OneShotAlarmTimer) {
   base::RunLoop().Run();
 
   EXPECT_TRUE(did_run);
-  }
 }
 
-TEST(AlarmTimerTest, OneShotAlarmTimer_Cancel) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_OneShotAlarmTimer_Cancel(
+    base::MessageLoop::Type message_loop_type) {
+  base::MessageLoop loop(message_loop_type);
 
   bool did_run_a = false;
-    OneShotAlarmTimerTester* a =
-        new OneShotAlarmTimerTester(&did_run_a, kTenMilliseconds);
+  OneShotAlarmTimerTester* a = new OneShotAlarmTimerTester(&did_run_a,
+                                                           kTenMilliseconds);
 
   // This should run before the timer expires.
   base::MessageLoop::current()->DeleteSoon(FROM_HERE, a);
@@ -161,14 +161,11 @@ TEST(AlarmTimerTest, OneShotAlarmTimer_Cancel) {
 
   EXPECT_FALSE(did_run_a);
   EXPECT_TRUE(did_run_b);
-  }
 }
 
-// If underlying timer does not handle this properly, we will crash or fail
-// in full page heap environment.
-TEST(AlarmTimerTest, OneShotSelfDeletingAlarmTimer) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_OneShotSelfDeletingAlarmTimer(
+    base::MessageLoop::Type message_loop_type) {
+  base::MessageLoop loop(message_loop_type);
 
   bool did_run = false;
   OneShotSelfDeletingAlarmTimerTester f(&did_run, kTenMilliseconds);
@@ -177,30 +174,28 @@ TEST(AlarmTimerTest, OneShotSelfDeletingAlarmTimer) {
   base::RunLoop().Run();
 
   EXPECT_TRUE(did_run);
-  }
 }
 
-TEST(AlarmTimerTest, RepeatingAlarmTimer) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_RepeatingAlarmTimer(base::MessageLoop::Type message_loop_type,
+                                 const base::TimeDelta& delay) {
+  base::MessageLoop loop(message_loop_type);
 
   bool did_run = false;
-    RepeatingAlarmTimerTester f(&did_run, kTenMilliseconds);
+  RepeatingAlarmTimerTester f(&did_run, delay);
   f.Start();
 
   base::RunLoop().Run();
 
   EXPECT_TRUE(did_run);
-  }
 }
 
-TEST(AlarmTimerTest, RepeatingAlarmTimer_Cancel) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_RepeatingAlarmTimer_Cancel(
+    base::MessageLoop::Type message_loop_type, const base::TimeDelta& delay) {
+  base::MessageLoop loop(message_loop_type);
 
   bool did_run_a = false;
-    RepeatingAlarmTimerTester* a =
-        new RepeatingAlarmTimerTester(&did_run_a, kTenMilliseconds);
+  RepeatingAlarmTimerTester* a = new RepeatingAlarmTimerTester(&did_run_a,
+                                                               delay);
 
   // This should run before the timer expires.
   base::MessageLoop::current()->DeleteSoon(FROM_HERE, a);
@@ -209,52 +204,66 @@ TEST(AlarmTimerTest, RepeatingAlarmTimer_Cancel) {
   a->Start();
 
   bool did_run_b = false;
-    RepeatingAlarmTimerTester b(&did_run_b, kTenMilliseconds);
+  RepeatingAlarmTimerTester b(&did_run_b, delay);
   b.Start();
 
   base::RunLoop().Run();
 
   EXPECT_FALSE(did_run_a);
   EXPECT_TRUE(did_run_b);
-  }
 }
 
-TEST(AlarmTimerTest, RepeatingAlarmTimerZeroDelay) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
-
-    bool did_run = false;
-    RepeatingAlarmTimerTester f(&did_run, base::TimeDelta());
-    f.Start();
+}  // namespace
 
-    base::RunLoop().Run();
+//-----------------------------------------------------------------------------
+// Each test is run against each type of MessageLoop.  That way we are sure
+// that timers work properly in all configurations.
 
-    EXPECT_TRUE(did_run);
+TEST(AlarmTimerTest, OneShotAlarmTimer) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_OneShotAlarmTimer(testing_message_loops[i]);
   }
 }
 
-TEST(AlarmTimerTest, RepeatingAlarmTimerZeroDelay_Cancel) {
+TEST(AlarmTimerTest, OneShotAlarmTimer_Cancel) {
   for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
-
-    bool did_run_a = false;
-    RepeatingAlarmTimerTester* a =
-        new RepeatingAlarmTimerTester(&did_run_a, base::TimeDelta());
+    RunTest_OneShotAlarmTimer_Cancel(testing_message_loops[i]);
+  }
+}
 
-    // This should run before the timer expires.
-    base::MessageLoop::current()->DeleteSoon(FROM_HERE, a);
+// If underlying timer does not handle this properly, we will crash or fail
+// in full page heap environment.
+TEST(AlarmTimerTest, OneShotSelfDeletingAlarmTimer) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_OneShotSelfDeletingAlarmTimer(testing_message_loops[i]);
+  }
+}
 
-    // Now start the timer.
-    a->Start();
+TEST(AlarmTimerTest, RepeatingAlarmTimer) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_RepeatingAlarmTimer(testing_message_loops[i],
+                                kTenMilliseconds);
+  }
+}
 
-    bool did_run_b = false;
-    RepeatingAlarmTimerTester b(&did_run_b, base::TimeDelta());
-    b.Start();
+TEST(AlarmTimerTest, RepeatingAlarmTimer_Cancel) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_RepeatingAlarmTimer_Cancel(testing_message_loops[i],
+                                       kTenMilliseconds);
+  }
+}
 
-    base::RunLoop().Run();
+TEST(AlarmTimerTest, RepeatingAlarmTimerZeroDelay) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_RepeatingAlarmTimer(testing_message_loops[i],
+                                base::TimeDelta::FromMilliseconds(0));
+  }
+}
 
-    EXPECT_FALSE(did_run_a);
-    EXPECT_TRUE(did_run_b);
+TEST(AlarmTimerTest, RepeatingAlarmTimerZeroDelay_Cancel) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_RepeatingAlarmTimer_Cancel(testing_message_loops[i],
+                                       base::TimeDelta::FromMilliseconds(0));
   }
 }
 
@@ -282,7 +291,7 @@ TEST(AlarmTimerTest, MessageLoopShutdown) {
 TEST(AlarmTimerTest, NonRepeatIsRunning) {
   {
     base::MessageLoop loop;
-    timers::OneShotAlarmTimer timer;
+    timers::AlarmTimer timer(false, false);
     EXPECT_FALSE(timer.IsRunning());
     timer.Start(FROM_HERE, base::TimeDelta::FromDays(1),
                 base::Bind(&base::DoNothing));
@@ -293,7 +302,7 @@ TEST(AlarmTimerTest, NonRepeatIsRunning) {
   }
 
   {
-    timers::SimpleAlarmTimer timer;
+    timers::AlarmTimer timer(true, false);
     base::MessageLoop loop;
     EXPECT_FALSE(timer.IsRunning());
     timer.Start(FROM_HERE, base::TimeDelta::FromDays(1),
@@ -308,7 +317,7 @@ TEST(AlarmTimerTest, NonRepeatIsRunning) {
 }
 
 TEST(AlarmTimerTest, NonRepeatMessageLoopDeath) {
-  timers::OneShotAlarmTimer timer;
+  timers::AlarmTimer timer(false, false);
   {
     base::MessageLoop loop;
     EXPECT_FALSE(timer.IsRunning());
@@ -322,8 +331,8 @@ TEST(AlarmTimerTest, NonRepeatMessageLoopDeath) {
 
 TEST(AlarmTimerTest, RetainRepeatIsRunning) {
   base::MessageLoop loop;
-  timers::RepeatingAlarmTimer timer(FROM_HERE, base::TimeDelta::FromDays(1),
-                                    base::Bind(&base::DoNothing));
+  timers::AlarmTimer timer(FROM_HERE, base::TimeDelta::FromDays(1),
+                          base::Bind(&base::DoNothing), true);
   EXPECT_FALSE(timer.IsRunning());
   timer.Reset();
   EXPECT_TRUE(timer.IsRunning());
@@ -335,8 +344,8 @@ TEST(AlarmTimerTest, RetainRepeatIsRunning) {
 
 TEST(AlarmTimerTest, RetainNonRepeatIsRunning) {
   base::MessageLoop loop;
-  timers::SimpleAlarmTimer timer(FROM_HERE, base::TimeDelta::FromDays(1),
-                                 base::Bind(&base::DoNothing));
+  timers::AlarmTimer timer(FROM_HERE, base::TimeDelta::FromDays(1),
+                          base::Bind(&base::DoNothing), false);
   EXPECT_FALSE(timer.IsRunning());
   timer.Reset();
   EXPECT_TRUE(timer.IsRunning());
@@ -372,7 +381,7 @@ TEST(AlarmTimerTest, ContinuationStopStart) {
   {
     ClearAllCallbackHappened();
     base::MessageLoop loop;
-    timers::OneShotAlarmTimer timer;
+    timers::AlarmTimer timer(false, false);
     timer.Start(FROM_HERE, base::TimeDelta::FromMilliseconds(10),
                 base::Bind(&SetCallbackHappened1));
     timer.Stop();
@@ -388,7 +397,7 @@ TEST(AlarmTimerTest, ContinuationReset) {
   {
     ClearAllCallbackHappened();
     base::MessageLoop loop;
-    timers::OneShotAlarmTimer timer;
+    timers::AlarmTimer timer(false, false);
     timer.Start(FROM_HERE, base::TimeDelta::FromMilliseconds(10),
                 base::Bind(&SetCallbackHappened1));
     timer.Reset();
@@ -401,6 +410,7 @@ TEST(AlarmTimerTest, ContinuationReset) {
 
 }  // namespace
 
+
 namespace {
 void TimerRanCallback(bool* did_run) {
   *did_run = true;
@@ -409,22 +419,18 @@ void TimerRanCallback(bool* did_run) {
       FROM_HERE, base::MessageLoop::QuitWhenIdleClosure());
 }
 
-TEST(AlarmTimerTest, OneShotTimerConcurrentResetAndTimerFired) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_OneShotTimerConcurrentResetAndTimerFired(
+    base::MessageLoop::Type message_loop_type) {
+  base::MessageLoop loop(message_loop_type);
 
-    timers::OneShotAlarmTimer timer;
+  timers::AlarmTimer timer(false, false);
   bool did_run = false;
 
-    base::RunLoop run_loop;
-
-    timer.SetTimerFiredCallbackForTest(run_loop.QuitClosure());
-    timer.Start(FROM_HERE, kTenMilliseconds,
-                base::Bind(&TimerRanCallback, &did_run));
+  timer.Start(
+      FROM_HERE, kTenMilliseconds, base::Bind(&TimerRanCallback, &did_run));
 
-    // Wait until the timer has fired and a task has been queue in the
-    // MessageLoop.
-    run_loop.Run();
+  // Sleep twice as long as the timer to ensure that the timer task gets queued.
+  base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(20));
 
   // Now reset the timer.  This is attempting to simulate the timer firing and
   // being reset at the same time.  The previously queued task should be
@@ -434,46 +440,54 @@ TEST(AlarmTimerTest, OneShotTimerConcurrentResetAndTimerFired) {
   base::RunLoop().RunUntilIdle();
   EXPECT_FALSE(did_run);
 
-    // If the previous check failed, running the message loop again will hang
-    // the test so we only do it if the callback has not run yet.
+  // If the previous check failed, running the message loop again will hang the
+  // test so we only do it if the callback has not run yet.
   if (!did_run) {
     base::RunLoop().Run();
     EXPECT_TRUE(did_run);
   }
-  }
 }
 
-TEST(AlarmTimerTest, RepeatingTimerConcurrentResetAndTimerFired) {
-  for (int i = 0; i < kNumTestingMessageLoops; i++) {
-    base::MessageLoop loop(testing_message_loops[i]);
+void RunTest_RepeatingTimerConcurrentResetAndTimerFired(
+    base::MessageLoop::Type message_loop_type) {
+  base::MessageLoop loop(message_loop_type);
 
-    timers::RepeatingAlarmTimer timer;
+  timers::AlarmTimer timer(true, true);
   bool did_run = false;
 
-    base::RunLoop run_loop;
-
-    timer.SetTimerFiredCallbackForTest(run_loop.QuitClosure());
-    timer.Start(FROM_HERE, kTenMilliseconds,
-                base::Bind(&TimerRanCallback, &did_run));
+  timer.Start(
+      FROM_HERE, kTenMilliseconds, base::Bind(&TimerRanCallback, &did_run));
 
-    // Wait until the timer has fired and a task has been queue in the
-    // MessageLoop.
-    run_loop.Run();
+  // Sleep more that three times as long as the timer duration to ensure that
+  // multiple tasks get queued.
+  base::PlatformThread::Sleep(base::TimeDelta::FromMilliseconds(35));
 
-    // Now reset the timer.  This is attempting to simulate the timer firing and
-    // being reset at the same time.  The previously queued task should be
-    // removed.
+  // Now reset the timer.  This is attempting to simulate a very busy message
+  // loop where multiple tasks get queued but the timer gets reset before any of
+  // them have a chance to run.
   timer.Reset();
 
   base::RunLoop().RunUntilIdle();
   EXPECT_FALSE(did_run);
 
-    // If the previous check failed, running the message loop again will hang
-    // the test so we only do it if the callback has not run yet.
+  // If the previous check failed, running the message loop again will hang the
+  // test so we only do it if the callback has not run yet.
   if (!did_run) {
     base::RunLoop().Run();
     EXPECT_TRUE(did_run);
   }
+}
+
+TEST(AlarmTimerTest, OneShotTimerConcurrentResetAndTimerFired) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_OneShotTimerConcurrentResetAndTimerFired(testing_message_loops[i]);
+  }
+}
+
+TEST(AlarmTimerTest, RepeatingTimerConcurrentResetAndTimerFired) {
+  for (int i = 0; i < kNumTestingMessageLoops; i++) {
+    RunTest_RepeatingTimerConcurrentResetAndTimerFired(
+        testing_message_loops[i]);
   }
 }
 

components/timers/rtc_alarm.cc

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/timers/rtc_alarm.h"
+
+#include <sys/timerfd.h>
+
+#include "base/bind.h"
+#include "base/files/file_util.h"
+#include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/macros.h"
+#include "base/message_loop/message_loop_proxy.h"
+#include "base/threading/thread.h"
+
+namespace timers {
+
+namespace {
+// Helper class to ensure that the IO thread we will use for watching file
+// descriptors is started only once.
+class IOThreadStartHelper {
+ public:
+  IOThreadStartHelper() : thread_(new base::Thread("RTC Alarm IO Thread")) {
+    CHECK(thread_->StartWithOptions(
+        base::Thread::Options(base::MessageLoop::TYPE_IO, 0)));
+  }
+  ~IOThreadStartHelper() {}
+
+  base::Thread& operator*() const { return *thread_.get(); }
+
+  base::Thread* operator->() const { return thread_.get(); }
+
+ private:
+  scoped_ptr<base::Thread> thread_;
+};
+
+base::LazyInstance<IOThreadStartHelper> g_io_thread = LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+RtcAlarm::RtcAlarm()
+    : alarm_fd_(timerfd_create(CLOCK_REALTIME_ALARM, 0)),
+      origin_event_id_(0),
+      io_event_id_(0) {
+}
+
+RtcAlarm::~RtcAlarm() {
+  if (alarm_fd_ != -1)
+    close(alarm_fd_);
+}
+
+bool RtcAlarm::Init(base::WeakPtr<AlarmTimer> parent) {
+  parent_ = parent;
+
+  return alarm_fd_ != -1;
+}
+
+void RtcAlarm::Stop() {
+  // Make sure that we stop the RTC from a MessageLoopForIO.
+  if (!base::MessageLoopForIO::IsCurrent()) {
+    g_io_thread.Get()->task_runner()->PostTask(
+        FROM_HERE,
+        base::Bind(&RtcAlarm::Stop, scoped_refptr<RtcAlarm>(this)));
+    return;
+  }
+
+  // Stop watching for events.
+  fd_watcher_.reset();
+
+  // Now clear the timer.
+  DCHECK_NE(alarm_fd_, -1);
+  itimerspec blank_time = {};
+  timerfd_settime(alarm_fd_, 0, &blank_time, NULL);
+}
+
+void RtcAlarm::Reset(base::TimeDelta delay) {
+  // Get a proxy for the current message loop.  When the timer fires, we will
+  // post tasks to this proxy to let the parent timer know.
+  origin_message_loop_ = base::MessageLoopProxy::current();
+
+  // Increment the event id.  Used to invalidate any events that have been
+  // queued but not yet run since the last time Reset() was called.
+  origin_event_id_++;
+
+  // Calling timerfd_settime with a zero delay actually clears the timer so if
+  // the user has requested a zero delay timer, we need to handle it
+  // differently.  We queue the task here but we still go ahead and call
+  // timerfd_settime with the zero delay anyway to cancel any previous delay
+  // that might have been programmed.
+  if (delay <= base::TimeDelta::FromMicroseconds(0)) {
+    // The timerfd_settime documentation is vague on what happens when it is
+    // passed a negative delay.  We can sidestep the issue by ensuring that the
+    // delay is 0.
+    delay = base::TimeDelta::FromMicroseconds(0);
+    origin_message_loop_->PostTask(FROM_HERE,
+                                   base::Bind(&RtcAlarm::OnTimerFired,
+                                              scoped_refptr<RtcAlarm>(this),
+                                              origin_event_id_));
+  }
+
+  // Make sure that we are running on a MessageLoopForIO.
+  if (!base::MessageLoopForIO::IsCurrent()) {
+    g_io_thread.Get()->task_runner()->PostTask(
+        FROM_HERE,
+        base::Bind(&RtcAlarm::ResetImpl,
+                   scoped_refptr<RtcAlarm>(this),
+                   delay,
+                   origin_event_id_));
+    return;
+  }
+
+  ResetImpl(delay, origin_event_id_);
+}
+
+void RtcAlarm::OnFileCanReadWithoutBlocking(int fd) {
+  DCHECK_EQ(alarm_fd_, fd);
+
+  // Read from the fd to ack the event.
+  char val[sizeof(uint64_t)];
+  base::ReadFromFD(alarm_fd_, val, sizeof(uint64_t));
+
+  // Make sure that the parent timer is informed on the proper message loop.
+  if (origin_message_loop_->RunsTasksOnCurrentThread()) {
+    OnTimerFired(io_event_id_);
+    return;
+  }
+
+  origin_message_loop_->PostTask(FROM_HERE,
+                                 base::Bind(&RtcAlarm::OnTimerFired,
+                                            scoped_refptr<RtcAlarm>(this),
+                                            io_event_id_));
+}
+
+void RtcAlarm::OnFileCanWriteWithoutBlocking(int fd) {
+  NOTREACHED();
+}
+
+void RtcAlarm::ResetImpl(base::TimeDelta delay, int event_id) {
+  DCHECK(base::MessageLoopForIO::IsCurrent());
+  DCHECK_NE(alarm_fd_, -1);
+
+  // Store the event id in the IO thread variable.  When the timer fires, we
+  // will bind this value to the OnTimerFired callback to ensure that we do the
+  // right thing if the timer gets reset.
+  io_event_id_ = event_id;
+
+  // If we were already watching the fd, this will stop watching it.
+  fd_watcher_.reset(new base::MessageLoopForIO::FileDescriptorWatcher);
+
+  // Start watching the fd to see when the timer fires.
+  if (!base::MessageLoopForIO::current()->WatchFileDescriptor(
+          alarm_fd_,
+          false,
+          base::MessageLoopForIO::WATCH_READ,
+          fd_watcher_.get(),
+          this)) {
+    LOG(ERROR) << "Error while attempting to watch file descriptor for RTC "
+               << "alarm.  Timer will not fire.";
+  }
+
+  // Actually set the timer.  This will also clear the pre-existing timer, if
+  // any.
+  itimerspec alarm_time = {};
+  alarm_time.it_value.tv_sec = delay.InSeconds();
+  alarm_time.it_value.tv_nsec =
+      (delay.InMicroseconds() % base::Time::kMicrosecondsPerSecond) *
+      base::Time::kNanosecondsPerMicrosecond;
+  if (timerfd_settime(alarm_fd_, 0, &alarm_time, NULL) < 0)
+    PLOG(ERROR) << "Error while setting alarm time.  Timer will not fire";
+}
+
+void RtcAlarm::OnTimerFired(int event_id) {
+  DCHECK(origin_message_loop_->RunsTasksOnCurrentThread());
+
+  // Check to make sure that the timer was not reset in the time between when
+  // this task was queued to run and now.  If it was reset, then don't do
+  // anything.
+  if (event_id != origin_event_id_)
+    return;
+
+  if (parent_)
+    parent_->OnTimerFired();
+}
+
+}  // namespace timers

components/timers/rtc_alarm.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_TIMER_RTC_ALARM_H_
+#define COMPONENTS_TIMER_RTC_ALARM_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/message_loop/message_loop.h"
+#include "base/time/time.h"
+#include "components/timers/alarm_timer.h"
+
+namespace base {
+class MessageLoopProxy;
+}
+
+namespace timers {
+// This class manages a Real Time Clock (RTC) alarm, a feature that is available
+// from linux version 3.11 onwards.  It creates a file descriptor for the RTC
+// alarm timer and then watches that file descriptor to see when it can be read
+// without blocking, indicating that the timer has fired.
+//
+// A major problem for this class is that watching file descriptors is only
+// available on a MessageLoopForIO but there is no guarantee the timer is going
+// to be created on one.  To get around this, the timer has a dedicated thread
+// with a MessageLoopForIO that posts tasks back to the thread that started the
+// timer.
+//
+// This class is designed to work together with the AlarmTimer class and is
+// tested through the AlarmTimer unit tests.  DO NOT TRY TO USE THIS CLASS
+// DIRECTLY.  Or use it anyway, I'm a comment not a cop.
+class RtcAlarm : public AlarmTimer::Delegate,
+                 public base::MessageLoopForIO::Watcher {
+ public:
+  RtcAlarm();
+
+  // AlarmTimer::Delegate overrides.
+  bool Init(base::WeakPtr<AlarmTimer> timer) override;
+  void Stop() override;
+  void Reset(base::TimeDelta delay) override;
+
+  // base::MessageLoopForIO::Watcher overrides.
+  void OnFileCanReadWithoutBlocking(int fd) override;
+  void OnFileCanWriteWithoutBlocking(int fd) override;
+
+ protected:
+  // Needs to be protected because AlarmTimer::Delegate is a refcounted class.
+  ~RtcAlarm() override;
+
+ private:
+  // Actually performs the system calls to set up the timer.  This must be
+  // called on a MessageLoopForIO.
+  void ResetImpl(base::TimeDelta delay, int event_id);
+
+  // Callback that is run when the timer fires.  Must be run on
+  // |origin_message_loop_|.
+  void OnTimerFired(int event_id);
+
+  // File descriptor associated with the alarm timer.
+  int alarm_fd_;
+
+  // Message loop which initially started the timer.
+  scoped_refptr<base::MessageLoopProxy> origin_message_loop_;
+
+  // The parent timer that should be informed when the timer fires.  We may end
+  // up outliving the parent so we need to ensure the reference is valid before
+  // we try to call it.
+  base::WeakPtr<AlarmTimer> parent_;
+
+  // Manages watching file descriptors.
+  scoped_ptr<base::MessageLoopForIO::FileDescriptorWatcher> fd_watcher_;
+
+  // These two variables are used for coordinating between the thread that
+  // started the timer and the IO thread being used to watch the timer file
+  // descriptor.  When Reset() is called, the original thread increments
+  // |origin_event_id_| and binds its value to ResetImpl(), which gets posted to
+  // the IO thread.  When the IO thread runs, it saves this value in
+  // |io_event_id_|.  Later, when the timer fires, the IO thread binds the value
+  // of |io_event_id_| to OnTimerFired() and posts it to the original thread.
+  // When the original thread runs OnTimerFired(), it calls
+  // parent_->OnTimerFired() only if |origin_event_id_| matches the event id
+  // that was passed in to it.  This is used to get around a race condition
+  // where the user resets the timer on the original thread, while the event is
+  // being fired on the IO thread at the same time.
+  int origin_event_id_;
+  int io_event_id_;
+
+  DISALLOW_COPY_AND_ASSIGN(RtcAlarm);
+};
+
+}  // namespace timers
+#endif  // COMPONENTS_TIMER_RTC_ALARM_H_