Use idle time to make progress on scheduled compilation jobs

BUG=v8:5215
R=rmcilroy@chromium.org,marja@chromium.org,vogelheim@chromium.org

Review-Url: https://codereview.chromium.org/2573493002
Cr-Commit-Position: refs/heads/master@{#41767}

src/compiler-dispatcher/compiler-dispatcher-job.cc

@@ -263,5 +263,36 @@ void CompilerDispatcherJob::ResetOnMainThread() {
   status_ = CompileJobStatus::kInitial;
 }
 
+double CompilerDispatcherJob::EstimateRuntimeOfNextStepInMs() const {
+  switch (status_) {
+    case CompileJobStatus::kInitial:
+      return tracer_->EstimatePrepareToParseInMs();
+
+    case CompileJobStatus::kReadyToParse:
+      return tracer_->EstimateParseInMs(parse_info_->end_position() -
+                                        parse_info_->start_position());
+
+    case CompileJobStatus::kParsed:
+      return tracer_->EstimateFinalizeParsingInMs();
+
+    case CompileJobStatus::kReadyToAnalyse:
+      return tracer_->EstimatePrepareToCompileInMs();
+
+    case CompileJobStatus::kReadyToCompile:
+      return tracer_->EstimateCompileInMs(
+          parse_info_->literal()->ast_node_count());
+
+    case CompileJobStatus::kCompiled:
+      return tracer_->EstimateFinalizeCompilingInMs();
+
+    case CompileJobStatus::kFailed:
+    case CompileJobStatus::kDone:
+      return 0.0;
+  }
+
+  UNREACHABLE();
+  return 0.0;
+}
+
 }  // namespace internal
 }  // namespace v8

src/compiler-dispatcher/compiler-dispatcher-job.h

@@ -83,6 +83,9 @@ class V8_EXPORT_PRIVATE CompilerDispatcherJob {
   // Transition from any state to kInitial and free all resources.
   void ResetOnMainThread();
 
+  // Estimate how long the next step will take using the tracer.
+  double EstimateRuntimeOfNextStepInMs() const;
+
  private:
   FRIEND_TEST(CompilerDispatcherJobTest, ScopeChain);
 

src/compiler-dispatcher/compiler-dispatcher-tracer.cc

@@ -16,6 +16,8 @@ double MonotonicallyIncreasingTimeInMs() {
          static_cast<double>(base::Time::kMillisecondsPerSecond);
 }
 
+const double kEstimatedRuntimeWithoutData = 1.0;
+
 }  // namespace
 
 CompilerDispatcherTracer::Scope::Scope(CompilerDispatcherTracer* tracer,
@@ -129,22 +131,23 @@ double CompilerDispatcherTracer::EstimateParseInMs(size_t source_length) const {
   return Estimate(parse_events_, source_length);
 }
 
-double CompilerDispatcherTracer::EstimateFinalizeParsingInMs() {
+double CompilerDispatcherTracer::EstimateFinalizeParsingInMs() const {
   base::LockGuard<base::Mutex> lock(&mutex_);
   return Average(finalize_parsing_events_);
 }
 
-double CompilerDispatcherTracer::EstimatePrepareToCompileInMs() {
+double CompilerDispatcherTracer::EstimatePrepareToCompileInMs() const {
   base::LockGuard<base::Mutex> lock(&mutex_);
   return Average(prepare_compile_events_);
 }
 
-double CompilerDispatcherTracer::EstimateCompileInMs(size_t ast_size_in_bytes) {
+double CompilerDispatcherTracer::EstimateCompileInMs(
+    size_t ast_size_in_bytes) const {
   base::LockGuard<base::Mutex> lock(&mutex_);
   return Estimate(compile_events_, ast_size_in_bytes);
 }
 
-double CompilerDispatcherTracer::EstimateFinalizeCompilingInMs() {
+double CompilerDispatcherTracer::EstimateFinalizeCompilingInMs() const {
   base::LockGuard<base::Mutex> lock(&mutex_);
   return Average(finalize_compiling_events_);
 }
@@ -158,7 +161,7 @@ double CompilerDispatcherTracer::Average(
 
 double CompilerDispatcherTracer::Estimate(
     const base::RingBuffer<std::pair<size_t, double>>& buffer, size_t num) {
-  if (buffer.Count() == 0) return 0.0;
+  if (buffer.Count() == 0) return kEstimatedRuntimeWithoutData;
   std::pair<size_t, double> sum = buffer.Sum(
       [](std::pair<size_t, double> a, std::pair<size_t, double> b) {
         return std::make_pair(a.first + b.first, a.second + b.second);

src/compiler-dispatcher/compiler-dispatcher-tracer.h

@@ -69,10 +69,10 @@ class V8_EXPORT_PRIVATE CompilerDispatcherTracer {
 
   double EstimatePrepareToParseInMs() const;
   double EstimateParseInMs(size_t source_length) const;
-  double EstimateFinalizeParsingInMs();
-  double EstimatePrepareToCompileInMs();
-  double EstimateCompileInMs(size_t ast_size_in_bytes);
-  double EstimateFinalizeCompilingInMs();
+  double EstimateFinalizeParsingInMs() const;
+  double EstimatePrepareToCompileInMs() const;
+  double EstimateCompileInMs(size_t ast_size_in_bytes) const;
+  double EstimateFinalizeCompilingInMs() const;
 
  private:
   static double Average(const base::RingBuffer<double>& buffer);

src/compiler-dispatcher/compiler-dispatcher.cc

@@ -4,6 +4,10 @@
 
 #include "src/compiler-dispatcher/compiler-dispatcher.h"
 
+#include "include/v8-platform.h"
+#include "include/v8.h"
+#include "src/base/platform/time.h"
+#include "src/cancelable-task.h"
 #include "src/compiler-dispatcher/compiler-dispatcher-job.h"
 #include "src/compiler-dispatcher/compiler-dispatcher-tracer.h"
 #include "src/objects-inl.h"
@@ -13,7 +17,12 @@ namespace internal {
 
 namespace {
 
-bool DoNextStepOnMainThread(CompilerDispatcherJob* job) {
+enum class ExceptionHandling { kSwallow, kThrow };
+
+bool DoNextStepOnMainThread(Isolate* isolate, CompilerDispatcherJob* job,
+                            ExceptionHandling exception_handling) {
+  DCHECK(ThreadId::Current().Equals(isolate->thread_id()));
+  v8::TryCatch try_catch(reinterpret_cast<v8::Isolate*>(isolate));
   switch (job->status()) {
     case CompileJobStatus::kInitial:
       job->PrepareToParseOnMainThread();
@@ -44,6 +53,11 @@ bool DoNextStepOnMainThread(CompilerDispatcherJob* job) {
       break;
   }
 
+  if (exception_handling == ExceptionHandling::kThrow &&
+      try_catch.HasCaught()) {
+    DCHECK(job->status() == CompileJobStatus::kFailed);
+    try_catch.ReThrow();
+  }
   return job->status() != CompileJobStatus::kFailed;
 }
 
@@ -52,14 +66,48 @@ bool IsFinished(CompilerDispatcherJob* job) {
          job->status() == CompileJobStatus::kFailed;
 }
 
+// Theoretically we get 50ms of idle time max, however it's unlikely that
+// we'll get all of it so try to be a conservative.
+const double kMaxIdleTimeToExpectInMs = 40;
+
 }  // namespace
 
-CompilerDispatcher::CompilerDispatcher(Isolate* isolate, size_t max_stack_size)
-    : isolate_(isolate),
-      max_stack_size_(max_stack_size),
-      tracer_(new CompilerDispatcherTracer(isolate_)) {}
+class CompilerDispatcher::IdleTask : public CancelableIdleTask {
+ public:
+  IdleTask(Isolate* isolate, CompilerDispatcher* dispatcher);
+  ~IdleTask() override;
 
-CompilerDispatcher::~CompilerDispatcher() {}
+  // CancelableIdleTask implementation.
+  void RunInternal(double deadline_in_seconds) override;
+
+ private:
+  CompilerDispatcher* dispatcher_;
+
+  DISALLOW_COPY_AND_ASSIGN(IdleTask);
+};
+
+CompilerDispatcher::IdleTask::IdleTask(Isolate* isolate,
+                                       CompilerDispatcher* dispatcher)
+    : CancelableIdleTask(isolate), dispatcher_(dispatcher) {}
+
+CompilerDispatcher::IdleTask::~IdleTask() {}
+
+void CompilerDispatcher::IdleTask::RunInternal(double deadline_in_seconds) {
+  dispatcher_->DoIdleWork(deadline_in_seconds);
+}
+
+CompilerDispatcher::CompilerDispatcher(Isolate* isolate, Platform* platform,
+                                       size_t max_stack_size)
+    : isolate_(isolate),
+      platform_(platform),
+      max_stack_size_(max_stack_size),
+      tracer_(new CompilerDispatcherTracer(isolate_)),
+      idle_task_scheduled_(false) {}
+
+CompilerDispatcher::~CompilerDispatcher() {
+  // To avoid crashing in unit tests due to unfished jobs.
+  AbortAll(BlockingBehavior::kBlock);
+}
 
 bool CompilerDispatcher::Enqueue(Handle<SharedFunctionInfo> function) {
   // We only handle functions (no eval / top-level code / wasm) that are
@@ -75,6 +123,7 @@ bool CompilerDispatcher::Enqueue(Handle<SharedFunctionInfo> function) {
   std::pair<int, int> key(Script::cast(function->script())->id(),
                           function->function_literal_id());
   jobs_.insert(std::make_pair(key, std::move(job)));
+  ScheduleIdleTaskIfNeeded();
   return true;
 }
 
@@ -89,9 +138,11 @@ bool CompilerDispatcher::FinishNow(Handle<SharedFunctionInfo> function) {
   // TODO(jochen): Check if there's an in-flight background task working on this
   // job.
   while (!IsFinished(job->second.get())) {
-    DoNextStepOnMainThread(job->second.get());
+    DoNextStepOnMainThread(isolate_, job->second.get(),
+                           ExceptionHandling::kThrow);
   }
   bool result = job->second->status() != CompileJobStatus::kFailed;
+  job->second->ResetOnMainThread();
   jobs_.erase(job);
   return result;
 }
@@ -104,6 +155,7 @@ void CompilerDispatcher::Abort(Handle<SharedFunctionInfo> function,
 
   // TODO(jochen): Check if there's an in-flight background task working on this
   // job.
+  job->second->ResetOnMainThread();
   jobs_.erase(job);
 }
 
@@ -111,6 +163,9 @@ void CompilerDispatcher::AbortAll(BlockingBehavior blocking) {
   USE(blocking);
   // TODO(jochen): Check if there's an in-flight background task working on this
   // job.
+  for (auto& kv : jobs_) {
+    kv.second->ResetOnMainThread();
+  }
   jobs_.clear();
 }
 
@@ -126,5 +181,54 @@ CompilerDispatcher::JobMap::const_iterator CompilerDispatcher::GetJobFor(
   return jobs_.end();
 }
 
+void CompilerDispatcher::ScheduleIdleTaskIfNeeded() {
+  v8::Isolate* v8_isolate = reinterpret_cast<v8::Isolate*>(isolate_);
+  if (!platform_->IdleTasksEnabled(v8_isolate)) return;
+  if (idle_task_scheduled_) return;
+  if (jobs_.empty()) return;
+  idle_task_scheduled_ = true;
+  platform_->CallIdleOnForegroundThread(v8_isolate,
+                                        new IdleTask(isolate_, this));
+}
+
+void CompilerDispatcher::DoIdleWork(double deadline_in_seconds) {
+  idle_task_scheduled_ = false;
+
+  // Number of jobs that are unlikely to make progress during any idle callback
+  // due to their estimated duration.
+  size_t too_long_jobs = 0;
+
+  // Iterate over all available jobs & remaining time. For each job, decide
+  // whether to 1) skip it (if it would take too long), 2) erase it (if it's
+  // finished), or 3) make progress on it.
+  double idle_time_in_seconds =
+      deadline_in_seconds - platform_->MonotonicallyIncreasingTime();
+  for (auto job = jobs_.begin();
+       job != jobs_.end() && idle_time_in_seconds > 0.0;
+       idle_time_in_seconds =
+           deadline_in_seconds - platform_->MonotonicallyIncreasingTime()) {
+    double estimate_in_ms = job->second->EstimateRuntimeOfNextStepInMs();
+    if (idle_time_in_seconds <
+        (estimate_in_ms /
+         static_cast<double>(base::Time::kMillisecondsPerSecond))) {
+      // If there's not enough time left, try to estimate whether we would
+      // have managed to finish the job in a large idle task to assess
+      // whether we should ask for another idle callback.
+      if (estimate_in_ms > kMaxIdleTimeToExpectInMs) ++too_long_jobs;
+      ++job;
+    } else if (IsFinished(job->second.get())) {
+      job->second->ResetOnMainThread();
+      job = jobs_.erase(job);
+      break;
+    } else {
+      // Do one step, and keep processing the job (as we don't advance the
+      // iterator).
+      DoNextStepOnMainThread(isolate_, job->second.get(),
+                             ExceptionHandling::kSwallow);
+    }
+  }
+  if (jobs_.size() > too_long_jobs) ScheduleIdleTaskIfNeeded();
+}
+
 }  // namespace internal
 }  // namespace v8

src/compiler-dispatcher/compiler-dispatcher.h

@@ -11,8 +11,12 @@
 
 #include "src/base/macros.h"
 #include "src/globals.h"
+#include "testing/gtest/include/gtest/gtest_prod.h"
 
 namespace v8 {
+
+class Platform;
+
 namespace internal {
 
 class CompilerDispatcherJob;
@@ -23,11 +27,14 @@ class SharedFunctionInfo;
 template <typename T>
 class Handle;
 
+// The CompilerDispatcher uses a combination of idle tasks and background tasks
+// to parse and compile lazily parsed functions.
 class V8_EXPORT_PRIVATE CompilerDispatcher {
  public:
   enum class BlockingBehavior { kBlock, kDontBlock };
 
-  CompilerDispatcher(Isolate* isolate, size_t max_stack_size);
+  CompilerDispatcher(Isolate* isolate, Platform* platform,
+                     size_t max_stack_size);
   ~CompilerDispatcher();
 
   // Returns true if a job was enqueued.
@@ -47,15 +54,24 @@ class V8_EXPORT_PRIVATE CompilerDispatcher {
   void AbortAll(BlockingBehavior blocking);
 
  private:
+  FRIEND_TEST(CompilerDispatcherTest, IdleTaskSmallIdleTime);
+
   typedef std::multimap<std::pair<int, int>,
                         std::unique_ptr<CompilerDispatcherJob>>
       JobMap;
+  class IdleTask;
+
   JobMap::const_iterator GetJobFor(Handle<SharedFunctionInfo> shared) const;
+  void ScheduleIdleTaskIfNeeded();
+  void DoIdleWork(double deadline_in_seconds);
 
   Isolate* isolate_;
+  Platform* platform_;
   size_t max_stack_size_;
   std::unique_ptr<CompilerDispatcherTracer> tracer_;
 
+  bool idle_task_scheduled_;
+
   // Mapping from (script id, function literal id) to job. We use a multimap,
   // as script id is not necessarily unique.
   JobMap jobs_;

src/isolate.cc

@@ -2518,7 +2518,8 @@ bool Isolate::Init(Deserializer* des) {
   cpu_profiler_ = new CpuProfiler(this);
   heap_profiler_ = new HeapProfiler(heap());
   interpreter_ = new interpreter::Interpreter(this);
-  compiler_dispatcher_ = new CompilerDispatcher(this, FLAG_stack_size);
+  compiler_dispatcher_ =
+      new CompilerDispatcher(this, V8::GetCurrentPlatform(), FLAG_stack_size);
 
   // Enable logging before setting up the heap
   logger_->SetUp(this);

test/unittests/compiler-dispatcher/compiler-dispatcher-tracer-unittest.cc

@@ -8,16 +8,16 @@
 namespace v8 {
 namespace internal {
 
-TEST(CompilerDispatcherTracerTest, EstimateZeroWithoutSamples) {
+TEST(CompilerDispatcherTracerTest, EstimateWithoutSamples) {
   CompilerDispatcherTracer tracer(nullptr);
 
   EXPECT_EQ(0.0, tracer.EstimatePrepareToParseInMs());
-  EXPECT_EQ(0.0, tracer.EstimateParseInMs(0));
-  EXPECT_EQ(0.0, tracer.EstimateParseInMs(42));
+  EXPECT_EQ(1.0, tracer.EstimateParseInMs(0));
+  EXPECT_EQ(1.0, tracer.EstimateParseInMs(42));
   EXPECT_EQ(0.0, tracer.EstimateFinalizeParsingInMs());
   EXPECT_EQ(0.0, tracer.EstimatePrepareToCompileInMs());
-  EXPECT_EQ(0.0, tracer.EstimateCompileInMs(0));
-  EXPECT_EQ(0.0, tracer.EstimateCompileInMs(42));
+  EXPECT_EQ(1.0, tracer.EstimateCompileInMs(0));
+  EXPECT_EQ(1.0, tracer.EstimateCompileInMs(42));
   EXPECT_EQ(0.0, tracer.EstimateFinalizeCompilingInMs());
 }
 
@@ -36,7 +36,7 @@ TEST(CompilerDispatcherTracerTest, Average) {
 TEST(CompilerDispatcherTracerTest, SizeBasedAverage) {
   CompilerDispatcherTracer tracer(nullptr);
 
-  EXPECT_EQ(0.0, tracer.EstimateParseInMs(100));
+  EXPECT_EQ(1.0, tracer.EstimateParseInMs(100));
 
   // All three samples parse 100 units/ms.
   tracer.RecordParse(1.0, 100);

test/unittests/compiler-dispatcher/compiler-dispatcher-unittest.cc

@@ -2,9 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include <memory>
-
 #include "src/compiler-dispatcher/compiler-dispatcher.h"
+
+#include "include/v8-platform.h"
+#include "src/compiler-dispatcher/compiler-dispatcher-job.h"
 #include "src/flags.h"
 #include "src/handles.h"
 #include "src/objects-inl.h"
@@ -17,45 +18,190 @@ namespace internal {
 
 typedef TestWithContext CompilerDispatcherTest;
 
+namespace {
+
+class MockPlatform : public v8::Platform {
+ public:
+  MockPlatform() : task_(nullptr), time_(0.0), time_step_(0.0) {}
+  ~MockPlatform() override = default;
+
+  void CallOnBackgroundThread(Task* task,
+                              ExpectedRuntime expected_runtime) override {
+    UNREACHABLE();
+  }
+
+  void CallOnForegroundThread(v8::Isolate* isolate, Task* task) override {
+    UNREACHABLE();
+  }
+
+  void CallDelayedOnForegroundThread(v8::Isolate* isolate, Task* task,
+                                     double delay_in_seconds) override {
+    UNREACHABLE();
+  }
+
+  void CallIdleOnForegroundThread(v8::Isolate* isolate,
+                                  IdleTask* task) override {
+    task_ = task;
+  }
+
+  bool IdleTasksEnabled(v8::Isolate* isolate) override { return true; }
+
+  double MonotonicallyIncreasingTime() override {
+    time_ += time_step_;
+    return time_;
+  }
+
+  void RunIdleTask(double deadline_in_seconds, double time_step) {
+    ASSERT_TRUE(task_ != nullptr);
+    time_step_ = time_step;
+    IdleTask* task = task_;
+    task_ = nullptr;
+    task->Run(deadline_in_seconds);
+    delete task;
+  }
+
+  bool IdleTaskPending() const { return !!task_; }
+
+ private:
+  IdleTask* task_;
+  double time_;
+  double time_step_;
+
+  DISALLOW_COPY_AND_ASSIGN(MockPlatform);
+};
+
+}  // namespace
+
 TEST_F(CompilerDispatcherTest, Construct) {
-  std::unique_ptr<CompilerDispatcher> dispatcher(
-      new CompilerDispatcher(i_isolate(), FLAG_stack_size));
+  MockPlatform platform;
+  CompilerDispatcher dispatcher(i_isolate(), &platform, FLAG_stack_size);
 }
 
 TEST_F(CompilerDispatcherTest, IsEnqueued) {
-  std::unique_ptr<CompilerDispatcher> dispatcher(
-      new CompilerDispatcher(i_isolate(), FLAG_stack_size));
+  MockPlatform platform;
+  CompilerDispatcher dispatcher(i_isolate(), &platform, FLAG_stack_size);
 
   const char script[] =
-      "function g() { var y = 1; function f(x) { return x * y }; return f; } "
+      "function g() { var y = 1; function f1(x) { return x * y }; return f1; } "
       "g();";
   Handle<JSFunction> f = Handle<JSFunction>::cast(RunJS(isolate(), script));
   Handle<SharedFunctionInfo> shared(f->shared(), i_isolate());
 
-  ASSERT_FALSE(dispatcher->IsEnqueued(shared));
-  ASSERT_TRUE(dispatcher->Enqueue(shared));
-  ASSERT_TRUE(dispatcher->IsEnqueued(shared));
-  dispatcher->Abort(shared, CompilerDispatcher::BlockingBehavior::kBlock);
-  ASSERT_FALSE(dispatcher->IsEnqueued(shared));
+  ASSERT_FALSE(dispatcher.IsEnqueued(shared));
+  ASSERT_TRUE(dispatcher.Enqueue(shared));
+  ASSERT_TRUE(dispatcher.IsEnqueued(shared));
+  dispatcher.Abort(shared, CompilerDispatcher::BlockingBehavior::kBlock);
+  ASSERT_FALSE(dispatcher.IsEnqueued(shared));
 }
 
 TEST_F(CompilerDispatcherTest, FinishNow) {
-  std::unique_ptr<CompilerDispatcher> dispatcher(
-      new CompilerDispatcher(i_isolate(), FLAG_stack_size));
+  MockPlatform platform;
+  CompilerDispatcher dispatcher(i_isolate(), &platform, FLAG_stack_size);
 
   const char script[] =
-      "function g() { var y = 1; function f(x) { return x * y }; return f; } "
+      "function g() { var y = 1; function f2(x) { return x * y }; return f2; } "
       "g();";
   Handle<JSFunction> f = Handle<JSFunction>::cast(RunJS(isolate(), script));
   Handle<SharedFunctionInfo> shared(f->shared(), i_isolate());
 
   ASSERT_FALSE(shared->HasBaselineCode());
-  ASSERT_TRUE(dispatcher->Enqueue(shared));
-  ASSERT_TRUE(dispatcher->FinishNow(shared));
+  ASSERT_TRUE(dispatcher.Enqueue(shared));
+  ASSERT_TRUE(dispatcher.FinishNow(shared));
   // Finishing removes the SFI from the queue.
-  ASSERT_FALSE(dispatcher->IsEnqueued(shared));
+  ASSERT_FALSE(dispatcher.IsEnqueued(shared));
   ASSERT_TRUE(shared->HasBaselineCode());
 }
 
+TEST_F(CompilerDispatcherTest, IdleTask) {
+  MockPlatform platform;
+  CompilerDispatcher dispatcher(i_isolate(), &platform, FLAG_stack_size);
+
+  const char script[] =
+      "function g() { var y = 1; function f3(x) { return x * y }; return f3; } "
+      "g();";
+  Handle<JSFunction> f = Handle<JSFunction>::cast(RunJS(isolate(), script));
+  Handle<SharedFunctionInfo> shared(f->shared(), i_isolate());
+
+  ASSERT_FALSE(platform.IdleTaskPending());
+  ASSERT_TRUE(dispatcher.Enqueue(shared));
+  ASSERT_TRUE(platform.IdleTaskPending());
+
+  // Since time doesn't progress on the MockPlatform, this is enough idle time
+  // to finish compiling the function.
+  platform.RunIdleTask(1000.0, 0.0);
+
+  ASSERT_FALSE(dispatcher.IsEnqueued(shared));
+  ASSERT_TRUE(shared->HasBaselineCode());
+}
+
+TEST_F(CompilerDispatcherTest, IdleTaskSmallIdleTime) {
+  MockPlatform platform;
+  CompilerDispatcher dispatcher(i_isolate(), &platform, FLAG_stack_size);
+
+  const char script[] =
+      "function g() { var y = 1; function f4(x) { return x * y }; return f4; } "
+      "g();";
+  Handle<JSFunction> f = Handle<JSFunction>::cast(RunJS(isolate(), script));
+  Handle<SharedFunctionInfo> shared(f->shared(), i_isolate());
+
+  ASSERT_FALSE(platform.IdleTaskPending());
+  ASSERT_TRUE(dispatcher.Enqueue(shared));
+  ASSERT_TRUE(platform.IdleTaskPending());
+
+  // The job should be scheduled for the main thread.
+  ASSERT_EQ(dispatcher.jobs_.size(), 1u);
+  ASSERT_TRUE(dispatcher.jobs_.begin()->second->status() ==
+              CompileJobStatus::kInitial);
+
+  // Only grant a little idle time and have time advance beyond it in one step.
+  platform.RunIdleTask(2.0, 1.0);
+
+  ASSERT_TRUE(dispatcher.IsEnqueued(shared));
+  ASSERT_FALSE(shared->HasBaselineCode());
+  ASSERT_TRUE(platform.IdleTaskPending());
+
+  // The job should be still scheduled for the main thread, but ready for
+  // parsing.
+  ASSERT_EQ(dispatcher.jobs_.size(), 1u);
+  ASSERT_TRUE(dispatcher.jobs_.begin()->second->status() ==
+              CompileJobStatus::kReadyToParse);
+
+  // Only grant a lot of idle time and freeze time.
+  platform.RunIdleTask(1000.0, 0.0);
+
+  ASSERT_FALSE(dispatcher.IsEnqueued(shared));
+  ASSERT_TRUE(shared->HasBaselineCode());
+  ASSERT_FALSE(platform.IdleTaskPending());
+}
+
+TEST_F(CompilerDispatcherTest, IdleTaskException) {
+  MockPlatform platform;
+  CompilerDispatcher dispatcher(i_isolate(), &platform, 50);
+
+  std::string script("function g() { function f5(x) { var a = ");
+  for (int i = 0; i < 1000; i++) {
+    script += "'x' + ";
+  }
+  script += " 'x'; }; return f5; } g();";
+  Handle<JSFunction> f =
+      Handle<JSFunction>::cast(RunJS(isolate(), script.c_str()));
+  Handle<SharedFunctionInfo> shared(f->shared(), i_isolate());
+
+  ASSERT_FALSE(platform.IdleTaskPending());
+  ASSERT_TRUE(dispatcher.Enqueue(shared));
+  ASSERT_TRUE(platform.IdleTaskPending());
+
+  // Idle tasks shouldn't leave exceptions behind.
+  v8::TryCatch try_catch(isolate());
+
+  // Since time doesn't progress on the MockPlatform, this is enough idle time
+  // to finish compiling the function.
+  platform.RunIdleTask(1000.0, 0.0);
+
+  ASSERT_FALSE(dispatcher.IsEnqueued(shared));
+  ASSERT_FALSE(shared->HasBaselineCode());
+  ASSERT_FALSE(try_catch.HasCaught());
+}
+
 }  // namespace internal
 }  // namespace v8