components: Introduce AlarmTimer class and use it for GCM heartbeat

components/timer/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/timer/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 timer {
+
+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()) {
+    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 timer