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// Copyright 2018 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 "base/base_export.h"
#include "base/macros.h"
#include "base/threading/thread.h"
#include "base/time/time.h"
#include "base/timer/timer.h"
namespace base {
namespace internal {
class TaskTracker;
// The TaskScheduler's ServiceThread is a mostly idle thread that is responsible
// for handling async events (e.g. delayed tasks and async I/O). Its role is to
// merely forward such events to their destination (hence staying mostly idle
// and highly responsive).
// It aliases Thread::Run() to enforce that ServiceThread::Run() be on the stack
// and make it easier to identify the service thread in stack traces.
class BASE_EXPORT ServiceThread : public Thread {
// Constructs a ServiceThread which will report latency metrics through
// |task_tracker| if non-null. In that case, this ServiceThread will assume a
// registered TaskScheduler instance and that |task_tracker| will outlive this
// ServiceThread.
explicit ServiceThread(const TaskTracker* task_tracker);
// Overrides the default interval at which |heartbeat_latency_timer_| fires.
// Call this with a |heartbeat| of zero to undo the override.
// Must not be called while the ServiceThread is running.
static void SetHeartbeatIntervalForTesting(TimeDelta heartbeat);
// Thread:
void Init() override;
void Run(RunLoop* run_loop) override;
// Kicks off a single async task which will record a histogram on the latency
// of a randomly chosen set of TaskTraits.
void PerformHeartbeatLatencyReport() const;
const TaskTracker* const task_tracker_;
// Fires a recurring heartbeat task to record latency histograms which are
// independent from any execution sequence. This is done on the service thread
// to avoid all external dependencies (even main thread).
base::RepeatingTimer heartbeat_latency_timer_;
} // namespace internal
} // namespace base