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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // The synthetic delay framework makes it possible to dynamically inject
      6 // arbitrary delays into into different parts of the codebase. This can be used,
      7 // for instance, for testing various task scheduling algorithms.
      8 //
      9 // The delays are specified in terms of a target duration for a given block of
     10 // code. If the code executes faster than the duration, the thread is made to
     11 // sleep until the deadline is met.
     12 //
     13 // Code can be instrumented for delays with two sets of macros. First, for
     14 // delays that should apply within a scope, use the following macro:
     15 //
     16 //   TRACE_EVENT_SYNTHETIC_DELAY("cc.LayerTreeHost.DrawAndSwap");
     17 //
     18 // For delaying operations that span multiple scopes, use:
     19 //
     20 //   TRACE_EVENT_SYNTHETIC_DELAY_BEGIN("cc.Scheduler.BeginMainFrame");
     21 //   ...
     22 //   TRACE_EVENT_SYNTHETIC_DELAY_END("cc.Scheduler.BeginMainFrame");
     23 //
     24 // Here BEGIN establishes the start time for the delay and END executes the
     25 // delay based on the remaining time. If BEGIN is called multiple times in a
     26 // row, END should be called a corresponding number of times. Only the last
     27 // call to END will have an effect.
     28 //
     29 // Note that a single delay may begin on one thread and end on another. This
     30 // implies that a single delay cannot not be applied in several threads at once.
     31 
     32 #ifndef BASE_TRACE_EVENT_TRACE_EVENT_SYNTHETIC_DELAY_H_
     33 #define BASE_TRACE_EVENT_TRACE_EVENT_SYNTHETIC_DELAY_H_
     34 
     35 #include "base/atomicops.h"
     36 #include "base/macros.h"
     37 #include "base/synchronization/lock.h"
     38 #include "base/time/time.h"
     39 #include "base/trace_event/trace_event.h"
     40 
     41 // Apply a named delay in the current scope.
     42 #define TRACE_EVENT_SYNTHETIC_DELAY(name)                                     \
     43   static base::subtle::AtomicWord INTERNAL_TRACE_EVENT_UID(impl_ptr) = 0;     \
     44   trace_event_internal::ScopedSyntheticDelay INTERNAL_TRACE_EVENT_UID(delay)( \
     45       name, &INTERNAL_TRACE_EVENT_UID(impl_ptr));
     46 
     47 // Begin a named delay, establishing its timing start point. May be called
     48 // multiple times as long as the calls to TRACE_EVENT_SYNTHETIC_DELAY_END are
     49 // balanced. Only the first call records the timing start point.
     50 #define TRACE_EVENT_SYNTHETIC_DELAY_BEGIN(name)                          \
     51   do {                                                                   \
     52     static base::subtle::AtomicWord impl_ptr = 0;                        \
     53     trace_event_internal::GetOrCreateDelay(name, &impl_ptr)->Begin();    \
     54   } while (false)
     55 
     56 // End a named delay. The delay is applied only if this call matches the
     57 // first corresponding call to TRACE_EVENT_SYNTHETIC_DELAY_BEGIN with the
     58 // same delay.
     59 #define TRACE_EVENT_SYNTHETIC_DELAY_END(name)                         \
     60   do {                                                                \
     61     static base::subtle::AtomicWord impl_ptr = 0;                     \
     62     trace_event_internal::GetOrCreateDelay(name, &impl_ptr)->End();   \
     63   } while (false)
     64 
     65 namespace base {
     66 namespace trace_event {
     67 
     68 // Time source for computing delay durations. Used for testing.
     69 class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelayClock {
     70  public:
     71   TraceEventSyntheticDelayClock();
     72   virtual ~TraceEventSyntheticDelayClock();
     73   virtual base::TimeTicks Now() = 0;
     74 
     75  private:
     76   DISALLOW_COPY_AND_ASSIGN(TraceEventSyntheticDelayClock);
     77 };
     78 
     79 // Single delay point instance.
     80 class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelay {
     81  public:
     82   enum Mode {
     83     STATIC,      // Apply the configured delay every time.
     84     ONE_SHOT,    // Apply the configured delay just once.
     85     ALTERNATING  // Apply the configured delay every other time.
     86   };
     87 
     88   // Returns an existing named delay instance or creates a new one with |name|.
     89   static TraceEventSyntheticDelay* Lookup(const std::string& name);
     90 
     91   void SetTargetDuration(TimeDelta target_duration);
     92   void SetMode(Mode mode);
     93   void SetClock(TraceEventSyntheticDelayClock* clock);
     94 
     95   // Begin the delay, establishing its timing start point. May be called
     96   // multiple times as long as the calls to End() are balanced. Only the first
     97   // call records the timing start point.
     98   void Begin();
     99 
    100   // End the delay. The delay is applied only if this call matches the first
    101   // corresponding call to Begin() with the same delay.
    102   void End();
    103 
    104   // Begin a parallel instance of the delay. Several parallel instances may be
    105   // active simultaneously and will complete independently. The computed end
    106   // time for the delay is stored in |out_end_time|, which should later be
    107   // passed to EndParallel().
    108   void BeginParallel(base::TimeTicks* out_end_time);
    109 
    110   // End a previously started parallel delay. |end_time| is the delay end point
    111   // computed by BeginParallel().
    112   void EndParallel(base::TimeTicks end_time);
    113 
    114  private:
    115   TraceEventSyntheticDelay();
    116   ~TraceEventSyntheticDelay();
    117   friend class TraceEventSyntheticDelayRegistry;
    118 
    119   void Initialize(const std::string& name,
    120                   TraceEventSyntheticDelayClock* clock);
    121   base::TimeTicks CalculateEndTimeLocked(base::TimeTicks start_time);
    122   void ApplyDelay(base::TimeTicks end_time);
    123 
    124   Lock lock_;
    125   Mode mode_;
    126   std::string name_;
    127   int begin_count_;
    128   int trigger_count_;
    129   base::TimeTicks end_time_;
    130   base::TimeDelta target_duration_;
    131   TraceEventSyntheticDelayClock* clock_;
    132 
    133   DISALLOW_COPY_AND_ASSIGN(TraceEventSyntheticDelay);
    134 };
    135 
    136 // Set the target durations of all registered synthetic delay points to zero.
    137 TRACE_EVENT_API_CLASS_EXPORT void ResetTraceEventSyntheticDelays();
    138 
    139 }  // namespace trace_event
    140 }  // namespace base
    141 
    142 namespace trace_event_internal {
    143 
    144 // Helper class for scoped delays. Do not use directly.
    145 class TRACE_EVENT_API_CLASS_EXPORT ScopedSyntheticDelay {
    146  public:
    147   explicit ScopedSyntheticDelay(const char* name,
    148                                 base::subtle::AtomicWord* impl_ptr);
    149   ~ScopedSyntheticDelay();
    150 
    151  private:
    152   base::trace_event::TraceEventSyntheticDelay* delay_impl_;
    153   base::TimeTicks end_time_;
    154 
    155   DISALLOW_COPY_AND_ASSIGN(ScopedSyntheticDelay);
    156 };
    157 
    158 // Helper for registering delays. Do not use directly.
    159 TRACE_EVENT_API_CLASS_EXPORT base::trace_event::TraceEventSyntheticDelay*
    160     GetOrCreateDelay(const char* name, base::subtle::AtomicWord* impl_ptr);
    161 
    162 }  // namespace trace_event_internal
    163 
    164 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_SYNTHETIC_DELAY_H_
    165