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// 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.
// The synthetic delay framework makes it possible to dynamically inject
// arbitrary delays into into different parts of the codebase. This can be used,
// for instance, for testing various task scheduling algorithms.
// The delays are specified in terms of a target duration for a given block of
// code. If the code executes faster than the duration, the thread is made to
// sleep until the deadline is met.
// Code can be instrumented for delays with two sets of macros. First, for
// delays that should apply within a scope, use the following macro:
// TRACE_EVENT_SYNTHETIC_DELAY("cc.LayerTreeHost.DrawAndSwap");
// For delaying operations that span multiple scopes, use:
// TRACE_EVENT_SYNTHETIC_DELAY_BEGIN("cc.Scheduler.BeginMainFrame");
// ...
// TRACE_EVENT_SYNTHETIC_DELAY_END("cc.Scheduler.BeginMainFrame");
// Here BEGIN establishes the start time for the delay and END executes the
// delay based on the remaining time. If BEGIN is called multiple times in a
// row, END should be called a corresponding number of times. Only the last
// call to END will have an effect.
// Note that a single delay may begin on one thread and end on another. This
// implies that a single delay cannot not be applied in several threads at once.
#include "base/atomicops.h"
#include "base/macros.h"
#include "base/synchronization/lock.h"
#include "base/time/time.h"
#include "base/trace_event/trace_event.h"
// Apply a named delay in the current scope.
static base::subtle::AtomicWord INTERNAL_TRACE_EVENT_UID(impl_ptr) = 0; \
trace_event_internal::ScopedSyntheticDelay INTERNAL_TRACE_EVENT_UID(delay)( \
name, &INTERNAL_TRACE_EVENT_UID(impl_ptr));
// Begin a named delay, establishing its timing start point. May be called
// multiple times as long as the calls to TRACE_EVENT_SYNTHETIC_DELAY_END are
// balanced. Only the first call records the timing start point.
do { \
static base::subtle::AtomicWord impl_ptr = 0; \
trace_event_internal::GetOrCreateDelay(name, &impl_ptr)->Begin(); \
} while (false)
// End a named delay. The delay is applied only if this call matches the
// first corresponding call to TRACE_EVENT_SYNTHETIC_DELAY_BEGIN with the
// same delay.
do { \
static base::subtle::AtomicWord impl_ptr = 0; \
trace_event_internal::GetOrCreateDelay(name, &impl_ptr)->End(); \
} while (false)
template <typename Type>
struct DefaultSingletonTraits;
namespace base {
namespace trace_event {
// Time source for computing delay durations. Used for testing.
class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelayClock {
virtual ~TraceEventSyntheticDelayClock();
virtual base::TimeTicks Now() = 0;
// Single delay point instance.
class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelay {
enum Mode {
STATIC, // Apply the configured delay every time.
ONE_SHOT, // Apply the configured delay just once.
ALTERNATING // Apply the configured delay every other time.
// Returns an existing named delay instance or creates a new one with |name|.
static TraceEventSyntheticDelay* Lookup(const std::string& name);
void SetTargetDuration(TimeDelta target_duration);
void SetMode(Mode mode);
void SetClock(TraceEventSyntheticDelayClock* clock);
// Begin the delay, establishing its timing start point. May be called
// multiple times as long as the calls to End() are balanced. Only the first
// call records the timing start point.
void Begin();
// End the delay. The delay is applied only if this call matches the first
// corresponding call to Begin() with the same delay.
void End();
// Begin a parallel instance of the delay. Several parallel instances may be
// active simultaneously and will complete independently. The computed end
// time for the delay is stored in |out_end_time|, which should later be
// passed to EndParallel().
void BeginParallel(base::TimeTicks* out_end_time);
// End a previously started parallel delay. |end_time| is the delay end point
// computed by BeginParallel().
void EndParallel(base::TimeTicks end_time);
friend class TraceEventSyntheticDelayRegistry;
void Initialize(const std::string& name,
TraceEventSyntheticDelayClock* clock);
base::TimeTicks CalculateEndTimeLocked(base::TimeTicks start_time);
void ApplyDelay(base::TimeTicks end_time);
Lock lock_;
Mode mode_;
std::string name_;
int begin_count_;
int trigger_count_;
base::TimeTicks end_time_;
base::TimeDelta target_duration_;
TraceEventSyntheticDelayClock* clock_;
// Set the target durations of all registered synthetic delay points to zero.
TRACE_EVENT_API_CLASS_EXPORT void ResetTraceEventSyntheticDelays();
} // namespace trace_event
} // namespace base
namespace trace_event_internal {
// Helper class for scoped delays. Do not use directly.
class TRACE_EVENT_API_CLASS_EXPORT ScopedSyntheticDelay {
explicit ScopedSyntheticDelay(const char* name,
base::subtle::AtomicWord* impl_ptr);
base::trace_event::TraceEventSyntheticDelay* delay_impl_;
base::TimeTicks end_time_;
// Helper for registering delays. Do not use directly.
TRACE_EVENT_API_CLASS_EXPORT base::trace_event::TraceEventSyntheticDelay*
GetOrCreateDelay(const char* name, base::subtle::AtomicWord* impl_ptr);
} // namespace trace_event_internal