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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_DEBUG_TRACE_EVENT_SYNTHETIC_DELAY_H_
     33 #define BASE_DEBUG_TRACE_EVENT_SYNTHETIC_DELAY_H_
     34 
     35 #include "base/atomicops.h"
     36 #include "base/debug/trace_event.h"
     37 #include "base/synchronization/lock.h"
     38 #include "base/time/time.h"
     39 
     40 // Apply a named delay in the current scope.
     41 #define TRACE_EVENT_SYNTHETIC_DELAY(name)                                     \
     42   static base::subtle::AtomicWord INTERNAL_TRACE_EVENT_UID(impl_ptr) = 0;     \
     43   trace_event_internal::ScopedSyntheticDelay INTERNAL_TRACE_EVENT_UID(delay)( \
     44       name, &INTERNAL_TRACE_EVENT_UID(impl_ptr));
     45 
     46 // Begin a named delay, establishing its timing start point. May be called
     47 // multiple times as long as the calls to TRACE_EVENT_SYNTHETIC_DELAY_END are
     48 // balanced. Only the first call records the timing start point.
     49 #define TRACE_EVENT_SYNTHETIC_DELAY_BEGIN(name)                          \
     50   do {                                                                   \
     51     static base::subtle::AtomicWord impl_ptr = 0;                        \
     52     trace_event_internal::GetOrCreateDelay(name, &impl_ptr)->Begin();    \
     53   } while (false)
     54 
     55 // End a named delay. The delay is applied only if this call matches the
     56 // first corresponding call to TRACE_EVENT_SYNTHETIC_DELAY_BEGIN with the
     57 // same delay.
     58 #define TRACE_EVENT_SYNTHETIC_DELAY_END(name)                         \
     59   do {                                                                \
     60     static base::subtle::AtomicWord impl_ptr = 0;                     \
     61     trace_event_internal::GetOrCreateDelay(name, &impl_ptr)->End();   \
     62   } while (false)
     63 
     64 template <typename Type>
     65 struct DefaultSingletonTraits;
     66 
     67 namespace base {
     68 namespace debug {
     69 
     70 // Time source for computing delay durations. Used for testing.
     71 class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelayClock {
     72  public:
     73   TraceEventSyntheticDelayClock();
     74   virtual ~TraceEventSyntheticDelayClock();
     75   virtual base::TimeTicks Now() = 0;
     76 
     77  private:
     78   DISALLOW_COPY_AND_ASSIGN(TraceEventSyntheticDelayClock);
     79 };
     80 
     81 // Single delay point instance.
     82 class TRACE_EVENT_API_CLASS_EXPORT TraceEventSyntheticDelay {
     83  public:
     84   enum Mode {
     85     STATIC,      // Apply the configured delay every time.
     86     ONE_SHOT,    // Apply the configured delay just once.
     87     ALTERNATING  // Apply the configured delay every other time.
     88   };
     89 
     90   // Returns an existing named delay instance or creates a new one with |name|.
     91   static TraceEventSyntheticDelay* Lookup(const std::string& name);
     92 
     93   void SetTargetDuration(TimeDelta target_duration);
     94   void SetMode(Mode mode);
     95   void SetClock(TraceEventSyntheticDelayClock* clock);
     96 
     97   // Begin the delay, establishing its timing start point. May be called
     98   // multiple times as long as the calls to End() are balanced. Only the first
     99   // call records the timing start point.
    100   void Begin();
    101 
    102   // End the delay. The delay is applied only if this call matches the first
    103   // corresponding call to Begin() with the same delay.
    104   void End();
    105 
    106   // Begin a parallel instance of the delay. Several parallel instances may be
    107   // active simultaneously and will complete independently. The computed end
    108   // time for the delay is stored in |out_end_time|, which should later be
    109   // passed to EndParallel().
    110   void BeginParallel(base::TimeTicks* out_end_time);
    111 
    112   // End a previously started parallel delay. |end_time| is the delay end point
    113   // computed by BeginParallel().
    114   void EndParallel(base::TimeTicks end_time);
    115 
    116  private:
    117   TraceEventSyntheticDelay();
    118   ~TraceEventSyntheticDelay();
    119   friend class TraceEventSyntheticDelayRegistry;
    120 
    121   void Initialize(const std::string& name,
    122                   TraceEventSyntheticDelayClock* clock);
    123   base::TimeTicks CalculateEndTimeLocked(base::TimeTicks start_time);
    124   void ApplyDelay(base::TimeTicks end_time);
    125 
    126   Lock lock_;
    127   Mode mode_;
    128   std::string name_;
    129   int begin_count_;
    130   int trigger_count_;
    131   base::TimeTicks end_time_;
    132   base::TimeDelta target_duration_;
    133   TraceEventSyntheticDelayClock* clock_;
    134 
    135   DISALLOW_COPY_AND_ASSIGN(TraceEventSyntheticDelay);
    136 };
    137 
    138 // Set the target durations of all registered synthetic delay points to zero.
    139 TRACE_EVENT_API_CLASS_EXPORT void ResetTraceEventSyntheticDelays();
    140 
    141 }  // namespace debug
    142 }  // namespace base
    143 
    144 namespace trace_event_internal {
    145 
    146 // Helper class for scoped delays. Do not use directly.
    147 class TRACE_EVENT_API_CLASS_EXPORT ScopedSyntheticDelay {
    148  public:
    149   explicit ScopedSyntheticDelay(const char* name,
    150                                 base::subtle::AtomicWord* impl_ptr);
    151   ~ScopedSyntheticDelay();
    152 
    153  private:
    154   base::debug::TraceEventSyntheticDelay* delay_impl_;
    155   base::TimeTicks end_time_;
    156 
    157   DISALLOW_COPY_AND_ASSIGN(ScopedSyntheticDelay);
    158 };
    159 
    160 // Helper for registering delays. Do not use directly.
    161 TRACE_EVENT_API_CLASS_EXPORT base::debug::TraceEventSyntheticDelay*
    162     GetOrCreateDelay(const char* name, base::subtle::AtomicWord* impl_ptr);
    163 
    164 }  // namespace trace_event_internal
    165 
    166 #endif /* BASE_DEBUG_TRACE_EVENT_SYNTHETIC_DELAY_H_ */
    167