Fixing --verify-predictable mode.

This CL fixes several sources of non-predictability by making Platform::MonotonicallyIncreasingTime() the only bottleneck for all time-querying functions and providing PredictablePlatform implementation.

Review URL: https://codereview.chromium.org/1415383004

Cr-Commit-Position: refs/heads/master@{#31959}

src/d8.cc

@@ -101,6 +101,48 @@ class MockArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
 };
 
 
+#ifndef V8_SHARED
+// Predictable v8::Platform implementation. All background and foreground
+// tasks are run immediately, delayed tasks are not executed at all.
+class PredictablePlatform : public Platform {
+ public:
+  PredictablePlatform() {}
+
+  void CallOnBackgroundThread(Task* task,
+                              ExpectedRuntime expected_runtime) override {
+    task->Run();
+    delete task;
+  }
+
+  void CallOnForegroundThread(v8::Isolate* isolate, Task* task) override {
+    task->Run();
+    delete task;
+  }
+
+  void CallDelayedOnForegroundThread(v8::Isolate* isolate, Task* task,
+                                     double delay_in_seconds) override {
+    delete task;
+  }
+
+  void CallIdleOnForegroundThread(v8::Isolate* isolate,
+                                  IdleTask* task) override {
+    UNREACHABLE();
+  }
+
+  bool IdleTasksEnabled(v8::Isolate* isolate) override { return false; }
+
+  double MonotonicallyIncreasingTime() override {
+    return synthetic_time_in_sec_ += 0.00001;
+  }
+
+ private:
+  double synthetic_time_in_sec_ = 0.0;
+
+  DISALLOW_COPY_AND_ASSIGN(PredictablePlatform);
+};
+#endif  // !V8_SHARED
+
+
 v8::Platform* g_platform = NULL;
 
 
@@ -425,13 +467,11 @@ int PerIsolateData::RealmIndexOrThrow(
 
 #ifndef V8_SHARED
 // performance.now() returns a time stamp as double, measured in milliseconds.
-// When FLAG_verify_predictable mode is enabled it returns current value
-// of Heap::allocations_count().
+// When FLAG_verify_predictable mode is enabled it returns result of
+// v8::Platform::MonotonicallyIncreasingTime().
 void Shell::PerformanceNow(const v8::FunctionCallbackInfo<v8::Value>& args) {
   if (i::FLAG_verify_predictable) {
-    Isolate* v8_isolate = args.GetIsolate();
-    i::Heap* heap = reinterpret_cast<i::Isolate*>(v8_isolate)->heap();
-    args.GetReturnValue().Set(heap->synthetic_time());
+    args.GetReturnValue().Set(g_platform->MonotonicallyIncreasingTime());
   } else {
     base::TimeDelta delta =
         base::TimeTicks::HighResolutionNow() - kInitialTicks;
@@ -2016,7 +2056,13 @@ void Shell::CollectGarbage(Isolate* isolate) {
 
 
 void Shell::EmptyMessageQueues(Isolate* isolate) {
-  while (v8::platform::PumpMessageLoop(g_platform, isolate)) continue;
+#ifndef V8_SHARED
+  if (!i::FLAG_verify_predictable) {
+#endif
+    while (v8::platform::PumpMessageLoop(g_platform, isolate)) continue;
+#ifndef V8_SHARED
+  }
+#endif
 }
 
 
@@ -2358,7 +2404,14 @@ int Shell::Main(int argc, char* argv[]) {
 #endif  // defined(_WIN32) || defined(_WIN64)
   if (!SetOptions(argc, argv)) return 1;
   v8::V8::InitializeICU(options.icu_data_file);
+#ifndef V8_SHARED
+  g_platform = i::FLAG_verify_predictable
+                   ? new PredictablePlatform()
+                   : v8::platform::CreateDefaultPlatform();
+#else
   g_platform = v8::platform::CreateDefaultPlatform();
+#endif  // !V8_SHARED
+
   v8::V8::InitializePlatform(g_platform);
   v8::V8::Initialize();
   if (options.natives_blob || options.snapshot_blob) {

src/execution.cc

@@ -497,6 +497,11 @@ void StackGuard::HandleGCInterrupt() {
 
 
 Object* StackGuard::HandleInterrupts() {
+  if (FLAG_verify_predictable) {
+    // Advance synthetic time by making a time request.
+    isolate_->heap()->MonotonicallyIncreasingTimeInMs();
+  }
+
   if (CheckAndClearInterrupt(GC_REQUEST)) {
     isolate_->heap()->HandleGCRequest();
   }

src/flag-definitions.h

@@ -829,6 +829,7 @@ DEFINE_NEG_IMPLICATION(predictable, concurrent_recompilation)
 DEFINE_NEG_IMPLICATION(predictable, concurrent_osr)
 DEFINE_NEG_IMPLICATION(predictable, concurrent_sweeping)
 DEFINE_NEG_IMPLICATION(predictable, parallel_compaction)
+DEFINE_NEG_IMPLICATION(predictable, memory_reducer)
 
 // mark-compact.cc
 DEFINE_BOOL(force_marking_deque_overflows, false,
@@ -1076,7 +1077,7 @@ DEFINE_IMPLICATION(print_all_code, trace_codegen)
 
 DEFINE_BOOL(verify_predictable, false,
             "this mode is used for checking that V8 behaves predictably")
-DEFINE_INT(dump_allocations_digest_at_alloc, 0,
+DEFINE_INT(dump_allocations_digest_at_alloc, -1,
            "dump allocations digest each n-th allocation")
 
 

src/heap/gc-tracer.cc

@@ -21,6 +21,19 @@ static intptr_t CountTotalHolesSize(Heap* heap) {
 }
 
 
+GCTracer::Scope::Scope(GCTracer* tracer, ScopeId scope)
+    : tracer_(tracer), scope_(scope) {
+  start_time_ = tracer_->heap_->MonotonicallyIncreasingTimeInMs();
+}
+
+
+GCTracer::Scope::~Scope() {
+  DCHECK(scope_ < NUMBER_OF_SCOPES);  // scope_ is unsigned.
+  tracer_->current_.scopes[scope_] +=
+      tracer_->heap_->MonotonicallyIncreasingTimeInMs() - start_time_;
+}
+
+
 GCTracer::AllocationEvent::AllocationEvent(double duration,
                                            size_t allocation_in_bytes) {
   duration_ = duration;
@@ -111,7 +124,7 @@ GCTracer::GCTracer(Heap* heap)
       combined_mark_compact_speed_cache_(0.0),
       start_counter_(0) {
   current_ = Event(Event::START, NULL, NULL);
-  current_.end_time = base::OS::TimeCurrentMillis();
+  current_.end_time = heap_->MonotonicallyIncreasingTimeInMs();
   previous_ = previous_incremental_mark_compactor_event_ = current_;
 }
 
@@ -851,7 +864,7 @@ size_t GCTracer::CurrentOldGenerationAllocationThroughputInBytesPerMillisecond()
 double GCTracer::ContextDisposalRateInMilliseconds() const {
   if (context_disposal_events_.size() < kRingBufferMaxSize) return 0.0;
 
-  double begin = base::OS::TimeCurrentMillis();
+  double begin = heap_->MonotonicallyIncreasingTimeInMs();
   double end = 0.0;
   ContextDisposalEventBuffer::const_iterator iter =
       context_disposal_events_.begin();

src/heap/gc-tracer.h

@@ -143,15 +143,8 @@ class GCTracer {
       NUMBER_OF_SCOPES
     };
 
-    Scope(GCTracer* tracer, ScopeId scope) : tracer_(tracer), scope_(scope) {
-      start_time_ = base::OS::TimeCurrentMillis();
-    }
-
-    ~Scope() {
-      DCHECK(scope_ < NUMBER_OF_SCOPES);  // scope_ is unsigned.
-      tracer_->current_.scopes[scope_] +=
-          base::OS::TimeCurrentMillis() - start_time_;
-    }
+    Scope(GCTracer* tracer, ScopeId scope);
+    ~Scope();
 
    private:
     GCTracer* tracer_;

src/heap/heap-inl.h

@@ -257,20 +257,21 @@ void Heap::OnAllocationEvent(HeapObject* object, int size_in_bytes) {
     profiler->AllocationEvent(object->address(), size_in_bytes);
   }
 
-  ++allocations_count_;
-
   if (FLAG_verify_predictable) {
+    ++allocations_count_;
+    // Advance synthetic time by making a time request.
+    MonotonicallyIncreasingTimeInMs();
+
     UpdateAllocationsHash(object);
     UpdateAllocationsHash(size_in_bytes);
 
-    if ((FLAG_dump_allocations_digest_at_alloc > 0) &&
-        (--dump_allocations_hash_countdown_ == 0)) {
-      dump_allocations_hash_countdown_ = FLAG_dump_allocations_digest_at_alloc;
+    if (allocations_count_ % FLAG_dump_allocations_digest_at_alloc == 0) {
       PrintAlloctionsHash();
     }
   }
 
   if (FLAG_trace_allocation_stack_interval > 0) {
+    if (!FLAG_verify_predictable) ++allocations_count_;
     if (allocations_count_ % FLAG_trace_allocation_stack_interval == 0) {
       isolate()->PrintStack(stdout, Isolate::kPrintStackConcise);
     }
@@ -292,14 +293,14 @@ void Heap::OnMoveEvent(HeapObject* target, HeapObject* source,
 
   if (FLAG_verify_predictable) {
     ++allocations_count_;
+    // Advance synthetic time by making a time request.
+    MonotonicallyIncreasingTimeInMs();
 
     UpdateAllocationsHash(source);
     UpdateAllocationsHash(target);
     UpdateAllocationsHash(size_in_bytes);
 
-    if ((FLAG_dump_allocations_digest_at_alloc > 0) &&
-        (--dump_allocations_hash_countdown_ == 0)) {
-      dump_allocations_hash_countdown_ = FLAG_dump_allocations_digest_at_alloc;
+    if (allocations_count_ % FLAG_dump_allocations_digest_at_alloc == 0) {
       PrintAlloctionsHash();
     }
   }

src/heap/heap.cc

@@ -102,7 +102,6 @@ Heap::Heap()
       gc_post_processing_depth_(0),
       allocations_count_(0),
       raw_allocations_hash_(0),
-      dump_allocations_hash_countdown_(FLAG_dump_allocations_digest_at_alloc),
       ms_count_(0),
       gc_count_(0),
       remembered_unmapped_pages_index_(0),
@@ -1056,7 +1055,7 @@ int Heap::NotifyContextDisposed(bool dependant_context) {
   }
   AgeInlineCaches();
   set_retained_maps(ArrayList::cast(empty_fixed_array()));
-  tracer()->AddContextDisposalTime(base::OS::TimeCurrentMillis());
+  tracer()->AddContextDisposalTime(MonotonicallyIncreasingTimeInMs());
   MemoryReducer::Event event;
   event.type = MemoryReducer::kContextDisposed;
   event.time_ms = MonotonicallyIncreasingTimeInMs();

src/heap/heap.h

@@ -888,10 +888,6 @@ class Heap {
   // Number of "runtime allocations" done so far.
   uint32_t allocations_count() { return allocations_count_; }
 
-  // Returns deterministic "time" value in ms. Works only with
-  // FLAG_verify_predictable.
-  double synthetic_time() { return allocations_count() / 2.0; }
-
   // Print short heap statistics.
   void PrintShortHeapStatistics();
 
@@ -2163,9 +2159,6 @@ class Heap {
   // Running hash over allocations performed.
   uint32_t raw_allocations_hash_;
 
-  // Countdown counter, dumps allocation hash when 0.
-  uint32_t dump_allocations_hash_countdown_;
-
   // How many mark-sweep collections happened.
   unsigned int ms_count_;
 

src/heap/incremental-marking.cc

@@ -786,7 +786,7 @@ void IncrementalMarking::Hurry() {
   if (state() == MARKING) {
     double start = 0.0;
     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
-      start = base::OS::TimeCurrentMillis();
+      start = heap_->MonotonicallyIncreasingTimeInMs();
       if (FLAG_trace_incremental_marking) {
         PrintF("[IncrementalMarking] Hurry\n");
       }
@@ -796,7 +796,7 @@ void IncrementalMarking::Hurry() {
     ProcessMarkingDeque();
     state_ = COMPLETE;
     if (FLAG_trace_incremental_marking || FLAG_print_cumulative_gc_stat) {
-      double end = base::OS::TimeCurrentMillis();
+      double end = heap_->MonotonicallyIncreasingTimeInMs();
       double delta = end - start;
       heap_->tracer()->AddMarkingTime(delta);
       if (FLAG_trace_incremental_marking) {
@@ -1058,7 +1058,7 @@ intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
   {
     HistogramTimerScope incremental_marking_scope(
         heap_->isolate()->counters()->gc_incremental_marking());
-    double start = base::OS::TimeCurrentMillis();
+    double start = heap_->MonotonicallyIncreasingTimeInMs();
 
     // The marking speed is driven either by the allocation rate or by the rate
     // at which we are having to check the color of objects in the write
@@ -1109,7 +1109,7 @@ intptr_t IncrementalMarking::Step(intptr_t allocated_bytes,
     // with marking.
     SpeedUp();
 
-    double end = base::OS::TimeCurrentMillis();
+    double end = heap_->MonotonicallyIncreasingTimeInMs();
     double duration = (end - start);
     // Note that we report zero bytes here when sweeping was in progress or
     // when we just started incremental marking. In these cases we did not

src/heap/mark-compact.cc

@@ -668,7 +668,8 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
   int area_size = space->AreaSize();
 
   // Pairs of (live_bytes_in_page, page).
-  std::vector<std::pair<int, Page*> > pages;
+  typedef std::pair<int, Page*> LiveBytesPagePair;
+  std::vector<LiveBytesPagePair> pages;
   pages.reserve(number_of_pages);
 
   PageIterator it(space);
@@ -739,7 +740,10 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
     // - the total size of evacuated objects does not exceed the specified
     // limit.
     // - fragmentation of (n+1)-th page does not exceed the specified limit.
-    std::sort(pages.begin(), pages.end());
+    std::sort(pages.begin(), pages.end(),
+              [](const LiveBytesPagePair& a, const LiveBytesPagePair& b) {
+                return a.first < b.first;
+              });
     for (size_t i = 0; i < pages.size(); i++) {
       int live_bytes = pages[i].first;
       int free_bytes = area_size - live_bytes;
@@ -1968,7 +1972,7 @@ void MarkCompactCollector::MarkLiveObjects() {
   GCTracer::Scope gc_scope(heap()->tracer(), GCTracer::Scope::MC_MARK);
   double start_time = 0.0;
   if (FLAG_print_cumulative_gc_stat) {
-    start_time = base::OS::TimeCurrentMillis();
+    start_time = heap_->MonotonicallyIncreasingTimeInMs();
   }
   // The recursive GC marker detects when it is nearing stack overflow,
   // and switches to a different marking system.  JS interrupts interfere
@@ -2058,7 +2062,8 @@ void MarkCompactCollector::MarkLiveObjects() {
   AfterMarking();
 
   if (FLAG_print_cumulative_gc_stat) {
-    heap_->tracer()->AddMarkingTime(base::OS::TimeCurrentMillis() - start_time);
+    heap_->tracer()->AddMarkingTime(heap_->MonotonicallyIncreasingTimeInMs() -
+                                    start_time);
   }
 }
 
@@ -4404,7 +4409,7 @@ void MarkCompactCollector::SweepSpaces() {
   GCTracer::Scope gc_scope(heap()->tracer(), GCTracer::Scope::MC_SWEEP);
   double start_time = 0.0;
   if (FLAG_print_cumulative_gc_stat) {
-    start_time = base::OS::TimeCurrentMillis();
+    start_time = heap_->MonotonicallyIncreasingTimeInMs();
   }
 
 #ifdef DEBUG
@@ -4456,7 +4461,7 @@ void MarkCompactCollector::SweepSpaces() {
   ReleaseEvacuationCandidates();
 
   if (FLAG_print_cumulative_gc_stat) {
-    heap_->tracer()->AddSweepingTime(base::OS::TimeCurrentMillis() -
+    heap_->tracer()->AddSweepingTime(heap_->MonotonicallyIncreasingTimeInMs() -
                                      start_time);
   }
 

src/isolate.cc

@@ -2242,7 +2242,7 @@ bool Isolate::Init(Deserializer* des) {
                heap_.amount_of_external_allocated_memory_at_last_global_gc_)),
            Internals::kAmountOfExternalAllocatedMemoryAtLastGlobalGCOffset);
 
-  time_millis_at_init_ = base::OS::TimeCurrentMillis();
+  time_millis_at_init_ = heap_.MonotonicallyIncreasingTimeInMs();
 
   heap_.NotifyDeserializationComplete();
 

src/isolate.h

@@ -939,7 +939,7 @@ class Isolate {
   bool initialized_from_snapshot() { return initialized_from_snapshot_; }
 
   double time_millis_since_init() {
-    return base::OS::TimeCurrentMillis() - time_millis_at_init_;
+    return heap_.MonotonicallyIncreasingTimeInMs() - time_millis_at_init_;
   }
 
   DateCache* date_cache() {

src/runtime/runtime-date.cc

@@ -88,8 +88,7 @@ RUNTIME_FUNCTION(Runtime_DateCurrentTime) {
   // the OS time.
   double millis;
   if (FLAG_verify_predictable) {
-    millis = 1388534400000.0;  // Jan 1 2014 00:00:00 GMT+0000
-    millis += Floor(isolate->heap()->synthetic_time());
+    millis = Floor(isolate->heap()->MonotonicallyIncreasingTimeInMs());
   } else {
     millis = Floor(base::OS::TimeCurrentMillis());
   }