SQM Fuzzer: Add support for multi-threading.

Adds support to sync the virtual clocks of the various
threads created throughout the porgram. This code doesn't
include cross-thread posting yet.

Bug: 852076
Change-Id: I7936f464f9bfbd35eed3840841c0d8b27c138edc
Reviewed-on: https://chromium-review.googlesource.com/1165145Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584149}

third_party/blink/renderer/platform/scheduler/BUILD.gn

@@ -245,6 +245,12 @@ source_set("scheduler_fuzzer_tests") {
       "base/sequence_manager_fuzzer_processor.cc",
       "base/sequence_manager_fuzzer_processor.h",
       "base/sequence_manager_fuzzer_processor_unittest.cc",
+      "base/simple_thread_impl.cc",
+      "base/simple_thread_impl.h",
+      "base/thread_data.cc",
+      "base/thread_data.h",
+      "base/thread_pool_manager.cc",
+      "base/thread_pool_manager.h",
     ]
 
     deps += [
@@ -261,6 +267,12 @@ fuzzer_test("sequence_manager_fuzzer") {
     "base/sequence_manager_fuzzer.cc",
     "base/sequence_manager_fuzzer_processor.cc",
     "base/sequence_manager_fuzzer_processor.h",
+    "base/simple_thread_impl.cc",
+    "base/simple_thread_impl.h",
+    "base/thread_data.cc",
+    "base/thread_data.h",
+    "base/thread_pool_manager.cc",
+    "base/thread_pool_manager.h",
   ]
 
   deps = [

third_party/blink/renderer/platform/scheduler/base/proto/sequence_manager_test_description.proto

@@ -21,7 +21,7 @@ message SequenceManagerTestDescription {
   }
 
   message Action {
-    // NEXT ID = 11
+    // NEXT ID = 12
 
     optional uint64 action_id = 1;
 
@@ -35,6 +35,7 @@ message SequenceManagerTestDescription {
       CreateQueueVoterAction create_queue_voter = 8;
       InsertFenceAction insert_fence = 9;
       RemoveFenceAction remove_fence = 10;
+      CreateThreadAction create_thread = 11;
     }
   }
 
@@ -145,5 +146,19 @@ message SequenceManagerTestDescription {
     optional uint64 task_queue_id = 2;
   }
 
-  repeated Action initial_actions = 1;
+  message CreateThreadAction {
+    // NEXT ID = 2
+
+    repeated Action initial_thread_actions = 1;
+  }
+
+  message InitialThread {
+    // NEXT ID = 3
+
+    optional uint64 action_id = 1;
+
+    required CreateThreadAction create_thread = 2;
+  }
+
+  repeated InitialThread main_thread_actions = 1;
 }

third_party/blink/renderer/platform/scheduler/base/sequence_manager_fuzzer.cc

@@ -12,9 +12,6 @@
 DEFINE_BINARY_PROTO_FUZZER(
     const base::sequence_manager::SequenceManagerTestDescription&
         fuzzer_input) {
-  // Dump code for debugging.
-  // TODO(farahcharab): Add code so that output looks more like the native
-  // function call.
   if (getenv("LPM_DUMP_NATIVE_INPUT")) {
     std::cout << fuzzer_input.DebugString() << std::endl;
   }

third_party/blink/renderer/platform/scheduler/base/sequence_manager_fuzzer_processor.h

@@ -5,14 +5,10 @@
 #ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_SEQUENCE_MANAGER_FUZZER_PROCESSOR_H_
 #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_SEQUENCE_MANAGER_FUZZER_PROCESSOR_H_
 
-#include <memory>
 #include <vector>
 
 #include "base/memory/scoped_refptr.h"
 #include "base/memory/weak_ptr.h"
-#include "base/task/sequence_manager/test/sequence_manager_for_test.h"
-#include "base/task/sequence_manager/test/test_task_queue.h"
-#include "base/test/test_mock_time_task_runner.h"
 #include "base/time/time.h"
 #include "third_party/blink/renderer/platform/platform_export.h"
 #include "third_party/blink/renderer/platform/scheduler/base/proto/sequence_manager_test_description.pb.h"
@@ -20,8 +16,15 @@
 namespace base {
 namespace sequence_manager {
 
+class ThreadData;
+class ThreadPoolManager;
+
 // Provides functionality to parse the fuzzer's test description and run the
 // relevant APIs.
+//
+// Warning: For unit testing purposes, the thread data of the threads managed by
+// the |thread_pool_manager_| should live for the scope of the main thread
+// entry function i.e RunTest.
 class PLATFORM_EXPORT SequenceManagerFuzzerProcessor {
  public:
   // Public interface used to parse the fuzzer's test description and
@@ -30,7 +33,7 @@ class PLATFORM_EXPORT SequenceManagerFuzzerProcessor {
 
  protected:
   struct TaskForTest {
-    TaskForTest(uint64_t id, uint64_t start, uint64_t end);
+    TaskForTest(uint64_t id, uint64_t start_time_ms, uint64_t end_time_ms);
     bool operator==(const TaskForTest& rhs) const;
 
     uint64_t task_id;
@@ -48,10 +51,12 @@ class PLATFORM_EXPORT SequenceManagerFuzzerProcessor {
       kCancelTask,
       kShutdownTaskQueue,
       kInsertFence,
-      kRemoveFence
+      kRemoveFence,
+      kCreateThread,
     };
 
-    ActionForTest(uint64_t id, ActionType type, uint64_t start);
+    ActionForTest(uint64_t id, ActionType type, uint64_t start_time_ms);
+
     bool operator==(const ActionForTest& rhs) const;
 
     uint64_t action_id;
@@ -59,102 +64,128 @@ class PLATFORM_EXPORT SequenceManagerFuzzerProcessor {
     uint64_t start_time_ms;
   };
 
-  SequenceManagerFuzzerProcessor();
-
-  explicit SequenceManagerFuzzerProcessor(bool log_for_testing);
-
-  void RunTest(const SequenceManagerTestDescription& description);
-
-  void RunAction(const SequenceManagerTestDescription::Action& action);
-
-  const std::vector<TaskForTest>& ordered_tasks() const;
-  const std::vector<ActionForTest>& ordered_actions() const;
-
- private:
   class Task {
    public:
-    Task(SequenceManagerFuzzerProcessor* processor);
+    Task(ThreadData* thread_data, SequenceManagerFuzzerProcessor* processor);
     ~Task() = default;
 
     void Execute(const SequenceManagerTestDescription::Task& task);
 
     bool is_running;
     SequenceManagerFuzzerProcessor* processor_;
+    ThreadData* thread_data_;
     base::WeakPtrFactory<Task> weak_ptr_factory_;
   };
 
-  struct TaskQueueWithVoters {
-    TaskQueueWithVoters(scoped_refptr<TestTaskQueue> task_queue)
-        : queue(std::move(task_queue)){};
+  SequenceManagerFuzzerProcessor();
 
-    scoped_refptr<TestTaskQueue> queue;
-    std::vector<std::unique_ptr<TaskQueue::QueueEnabledVoter>> voters;
-  };
+  explicit SequenceManagerFuzzerProcessor(bool log_for_testing);
+
+  ~SequenceManagerFuzzerProcessor();
 
+  void RunTest(const SequenceManagerTestDescription& description);
+
+  void ExecuteThread(
+      ThreadData* thread_data,
+      const google::protobuf::RepeatedPtrField<
+          SequenceManagerTestDescription::Action>& initial_thread_actions);
+
+  // Returns an ordered list of tasks executed on each thread. Note that the
+  // ordering of the threads isn't deterministic since it follows the order in
+  // which the threads were constructed. Furthermore, given that
+  // ThreadPoolManager::CreateThread is used to construct these threads and
+  // given that it can be called from multiple threads, the order of
+  // construction isn't deterministic.
+  const std::vector<std::vector<TaskForTest>>& ordered_tasks() const;
+
+  // Returns an ordered list of actions executed on each thread. Note that the
+  // ordering of the threads isn't deterministic. For more details, check the
+  // comment above on ordered_tasks().
+  const std::vector<std::vector<ActionForTest>>& ordered_actions() const;
+
+ private:
+  friend class ThreadData;
+  friend class ThreadPoolManager;
+
+  void RunAction(ThreadData* thread_data,
+                 const SequenceManagerTestDescription::Action& action);
+
+  void ExecuteCreateThreadAction(
+      ThreadData* thread_data,
+      uint64_t action_id,
+      const SequenceManagerTestDescription::CreateThreadAction& action);
   void ExecuteCreateTaskQueueAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::CreateTaskQueueAction& action);
   void ExecutePostDelayedTaskAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::PostDelayedTaskAction& action);
   void ExecuteSetQueuePriorityAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::SetQueuePriorityAction& action);
   void ExecuteSetQueueEnabledAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::SetQueueEnabledAction& action);
   void ExecuteCreateQueueVoterAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::CreateQueueVoterAction& action);
   void ExecuteShutdownTaskQueueAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::ShutdownTaskQueueAction& action);
   void ExecuteCancelTaskAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::CancelTaskAction& action);
   void ExecuteInsertFenceAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::InsertFenceAction& action);
   void ExecuteRemoveFenceAction(
+      ThreadData* thread_data,
       uint64_t action_id,
       const SequenceManagerTestDescription::RemoveFenceAction& action);
 
-  void ExecuteTask(const SequenceManagerTestDescription::Task& task);
+  void ExecuteTask(ThreadData* thread_data,
+                   const SequenceManagerTestDescription::Task& task);
 
   void DeleteTask(Task* task);
 
-  void LogTaskForTesting(uint64_t task_id,
+  void LogTaskForTesting(ThreadData* thread_data,
+                         uint64_t task_id,
                          TimeTicks start_time,
                          TimeTicks end_time);
 
-  void LogActionForTesting(uint64_t action_id,
+  void LogActionForTesting(ThreadData* thread_data,
+                           uint64_t action_id,
                            ActionForTest::ActionType type,
                            TimeTicks start_time);
 
-  // Bound to current thread. Used to control the clock of the task queue
-  // manager.
-  scoped_refptr<TestMockTimeTaskRunner> test_task_runner_;
-
-  std::unique_ptr<SequenceManagerForTest> manager_;
-
-  // For testing purposes, this should follow the order in which the queues were
-  // created.
-  std::vector<TaskQueueWithVoters> task_queues_;
-
-  // Used to be able to cancel pending tasks from the sequence manager. For
-  // testing purposes, this should follow the order in which the tasks were
-  // posted.
-  std::vector<std::unique_ptr<Task>> pending_tasks_;
-
   const bool log_for_testing_;
 
   TimeTicks initial_time_;
 
-  // For Testing. Used to log tasks in their order of execution.
-  std::vector<TaskForTest> ordered_tasks_;
+  std::unique_ptr<ThreadPoolManager> thread_pool_manager_;
+
+  // The clock of the main thread data task runner is initialized to
+  // |initial_time_| and never advanced, since it can only execute actions at
+  // the start of the program.
+  std::unique_ptr<ThreadData> main_thread_data_;
+
+  // For Testing. Each entry contains the ordered list of tasks for one of the
+  // created threads. The first entry is reserved for the main thread (which is
+  // always empty since no tasks are executed on the main thread).
+  std::vector<std::vector<TaskForTest>> ordered_tasks_;
 
-  // For Testing. Used to log actions in their order of execution.
-  std::vector<ActionForTest> ordered_actions_;
+  // For Testing. Each entry contains the ordered list of actions for one of the
+  // created threads. The first entry is reserved for the main thread (which
+  // can only contain ActionType::kCreateThread actions).
+  std::vector<std::vector<ActionForTest>> ordered_actions_;
 };
 
 }  // namespace sequence_manager

third_party/blink/renderer/platform/scheduler/base/simple_thread_impl.cc

+#include "third_party/blink/renderer/platform/scheduler/base/simple_thread_impl.h"
+
+namespace base {
+namespace sequence_manager {
+
+SimpleThreadImpl::SimpleThreadImpl(ThreadCallback callback,
+                                   TimeTicks initial_time)
+    : SimpleThread("TestThread"),
+      callback_(std::move(callback)),
+      initial_time_(initial_time) {}
+
+void SimpleThreadImpl::Run() {
+  std::unique_ptr<ThreadData> thread_data =
+      std::make_unique<ThreadData>(initial_time_);
+  thread_data_ = thread_data.get();
+  std::move(callback_).Run(thread_data_);
+  thread_can_shutdown_.Wait();
+}
+
+SimpleThreadImpl::~SimpleThreadImpl() {
+  thread_can_shutdown_.Signal();
+  Join();
+}
+
+ThreadData* SimpleThreadImpl::thread_data() const {
+  return thread_data_;
+}
+
+}  // namespace sequence_manager
+}  // namespace base

third_party/blink/renderer/platform/scheduler/base/simple_thread_impl.h

+// Copyright 2018 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
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_SIMPLE_THREAD_IMPL_H_
+#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_SIMPLE_THREAD_IMPL_H_
+
+#include "base/callback.h"
+#include "base/synchronization/waitable_event.h"
+#include "base/threading/simple_thread.h"
+#include "third_party/blink/renderer/platform/platform_export.h"
+#include "third_party/blink/renderer/platform/scheduler/base/thread_data.h"
+
+namespace base {
+namespace sequence_manager {
+
+// Used by the ThreadPoolManager to create threads that do not have an
+// associated message loop, since we want to use base::TestMockTimeTaskRunner to
+// control the task execution and the clock of the thread.
+class PLATFORM_EXPORT SimpleThreadImpl : public SimpleThread {
+ public:
+  using ThreadCallback = base::OnceCallback<void(ThreadData*)>;
+
+  SimpleThreadImpl(ThreadCallback callback, TimeTicks initial_time);
+
+  ~SimpleThreadImpl() override;
+
+  ThreadData* thread_data() const;
+
+ private:
+  // This doesn't terminate until |this| object is destructed.
+  void Run() override;
+
+  ThreadCallback callback_;
+
+  // Time in which the thread is created.
+  TimeTicks initial_time_;
+
+  // The object pointed to by |thread_data_| is created and destructed from the
+  // Run function. This is necessary since it has to be constructed from the
+  // thread it should be bound to and destructed from the same thread.
+  ThreadData* thread_data_;
+
+  // Used by the Run function to only terminate when |this| is destructed, and
+  // this is used so that |thread_data_| will live as long as |this|.
+  WaitableEvent thread_can_shutdown_;
+};
+
+}  // namespace sequence_manager
+}  // namespace base
+
+#endif

third_party/blink/renderer/platform/scheduler/base/thread_data.cc

+#include "third_party/blink/renderer/platform/scheduler/base/thread_data.h"
+
+#include "base/task/sequence_manager/test/test_task_queue.h"
+#include "base/threading/thread_task_runner_handle.h"
+
+namespace base {
+namespace sequence_manager {
+
+ThreadData::ThreadData(TimeTicks initial_time) {
+  test_task_runner_ = WrapRefCounted(
+      new TestMockTimeTaskRunner(TestMockTimeTaskRunner::Type::kBoundToThread));
+
+  DCHECK(!(initial_time - TimeTicks()).is_zero())
+      << "A zero clock is not allowed as empty TimeTicks have a special value "
+         "(i.e. base::TimeTicks::is_null())";
+
+  test_task_runner_->AdvanceMockTickClock(initial_time - TimeTicks());
+
+  manager_ =
+      SequenceManagerForTest::Create(nullptr, ThreadTaskRunnerHandle::Get(),
+                                     test_task_runner_->GetMockTickClock());
+
+  TaskQueue::Spec spec = TaskQueue::Spec("default_task_queue");
+  task_queues_.emplace_back(manager_->CreateTaskQueue<TestTaskQueue>(spec));
+}
+
+ThreadData::~ThreadData() = default;
+
+}  // namespace sequence_manager
+}  // namespace base

third_party/blink/renderer/platform/scheduler/base/thread_data.h

+// Copyright 2018 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
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_THREAD_DATA_H_
+#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_THREAD_DATA_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/memory/scoped_refptr.h"
+#include "base/task/sequence_manager/test/sequence_manager_for_test.h"
+#include "base/task/sequence_manager/test/test_task_queue.h"
+#include "base/test/test_mock_time_task_runner.h"
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "third_party/blink/renderer/platform/platform_export.h"
+#include "third_party/blink/renderer/platform/scheduler/base/sequence_manager_fuzzer_processor.h"
+
+namespace base {
+namespace sequence_manager {
+
+class PLATFORM_EXPORT ThreadData {
+ public:
+  struct TaskQueueWithVoters {
+    explicit TaskQueueWithVoters(scoped_refptr<TestTaskQueue> task_queue)
+        : queue(std::move(task_queue)){};
+
+    scoped_refptr<TestTaskQueue> queue;
+    std::vector<std::unique_ptr<TaskQueue::QueueEnabledVoter>> voters;
+  };
+
+  // |initial_time| is the time in which |this| was instantiated.
+  explicit ThreadData(TimeTicks initial_time);
+
+  ~ThreadData();
+
+  // Bound to the thread in which this object was instantiated. Used to
+  // control the clock of the sequence manager.
+  scoped_refptr<TestMockTimeTaskRunner> test_task_runner_;
+
+  std::unique_ptr<SequenceManagerForTest> manager_;
+
+  // For testing purposes, this should follow the order in which queues
+  // were created on the thread in which |this| was instantiated.
+  std::vector<TaskQueueWithVoters> task_queues_;
+
+  // Used to be able to cancel pending tasks from the sequence manager. For
+  // testing purposes, this should follow the order in which the tasks were
+  // posted to the thread in which |this| was instantiated.
+  std::vector<std::unique_ptr<SequenceManagerFuzzerProcessor::Task>>
+      pending_tasks_;
+
+  // For Testing. Used to log tasks in their order of execution on the
+  // thread in which |this| was instantiated.
+  std::vector<SequenceManagerFuzzerProcessor::TaskForTest> ordered_tasks_;
+
+  // For Testing. Used to log actions in their order of execution on the
+  // thread in which |this| was instantiated.
+  std::vector<SequenceManagerFuzzerProcessor::ActionForTest> ordered_actions_;
+
+  THREAD_CHECKER(thread_checker_);
+};
+
+}  // namespace sequence_manager
+}  // namespace base
+
+#endif

third_party/blink/renderer/platform/scheduler/base/thread_pool_manager.cc

+#include "third_party/blink/renderer/platform/scheduler/base/thread_pool_manager.h"
+
+#include <algorithm>
+
+#include "base/bind.h"
+#include "third_party/blink/renderer/platform/scheduler/base/sequence_manager_fuzzer_processor.h"
+#include "third_party/blink/renderer/platform/scheduler/base/simple_thread_impl.h"
+#include "third_party/blink/renderer/platform/scheduler/base/thread_data.h"
+
+namespace base {
+namespace sequence_manager {
+
+ThreadPoolManager::ThreadPoolManager(SequenceManagerFuzzerProcessor* processor)
+    : processor_(processor),
+      next_time_(TimeTicks::Max()),
+      ready_to_compute_time_(&lock_),
+      ready_to_advance_time_(&lock_),
+      ready_to_terminate_(&lock_),
+      ready_to_execute_threads_(&lock_),
+      ready_for_next_round_(&lock_),
+      threads_waiting_to_compute_time_(0),
+      threads_waiting_to_advance_time_(0),
+      threads_ready_for_next_round_(0),
+      threads_ready_to_terminate_(0),
+      all_threads_ready_(true),
+      initial_threads_created_(false) {
+  DCHECK(processor_);
+};
+
+ThreadPoolManager::~ThreadPoolManager() = default;
+
+void ThreadPoolManager::CreateThread(
+    const google::protobuf::RepeatedPtrField<
+        SequenceManagerTestDescription::Action>& initial_thread_actions,
+    TimeTicks time) {
+  SimpleThreadImpl* thread;
+  {
+    AutoLock lock(lock_);
+    threads_.push_back(std::make_unique<SimpleThreadImpl>(
+        BindOnce(&ThreadPoolManager::StartThread, Unretained(this),
+                 initial_thread_actions),
+        time));
+    thread = threads_.back().get();
+  }
+  thread->Start();
+}
+
+void ThreadPoolManager::StartThread(
+    const google::protobuf::RepeatedPtrField<
+        SequenceManagerTestDescription::Action>& initial_thread_actions,
+    ThreadData* thread_data) {
+  {
+    AutoLock lock(lock_);
+    while (!initial_threads_created_)
+      ready_to_execute_threads_.Wait();
+  }
+  processor_->ExecuteThread(thread_data, initial_thread_actions);
+}
+
+void ThreadPoolManager::AdvanceClockSynchronouslyByPendingTaskDelay(
+    ThreadData* thread_data) {
+  DCHECK_CALLED_ON_VALID_THREAD(thread_data->thread_checker_);
+
+  ThreadReadyToComputeTime();
+
+  {
+    AutoLock lock(lock_);
+    while (threads_waiting_to_compute_time_ != threads_.size())
+      ready_to_compute_time_.Wait();
+    next_time_ = std::min(
+        next_time_,
+        thread_data->test_task_runner_->GetMockTickClock()->NowTicks() +
+            std::max(TimeDelta::FromMilliseconds(0),
+                     thread_data->test_task_runner_->NextPendingTaskDelay()));
+    threads_waiting_to_advance_time_++;
+    if (threads_waiting_to_advance_time_ == threads_.size()) {
+      threads_waiting_to_compute_time_ = 0;
+      ready_to_advance_time_.Broadcast();
+    }
+  }
+
+  AdvanceThreadClock(thread_data);
+}
+
+void ThreadPoolManager::AdvanceClockSynchronouslyToTime(ThreadData* thread_data,
+                                                        TimeTicks time) {
+  ThreadReadyToComputeTime();
+  {
+    AutoLock lock(lock_);
+    while (threads_waiting_to_compute_time_ != threads_.size())
+      ready_to_compute_time_.Wait();
+    next_time_ = std::min(next_time_, time);
+    threads_waiting_to_advance_time_++;
+    if (threads_waiting_to_advance_time_ == threads_.size()) {
+      threads_waiting_to_compute_time_ = 0;
+      ready_to_advance_time_.Broadcast();
+    }
+  }
+  AdvanceThreadClock(thread_data);
+}
+
+void ThreadPoolManager::ThreadReadyToComputeTime() {
+  AutoLock lock(lock_);
+  while (!all_threads_ready_)
+    ready_for_next_round_.Wait();
+  threads_waiting_to_compute_time_++;
+  if (threads_waiting_to_compute_time_ == threads_.size()) {
+    all_threads_ready_ = false;
+    ready_to_compute_time_.Broadcast();
+  }
+}
+
+void ThreadPoolManager::AdvanceThreadClock(ThreadData* thread_data) {
+  AutoLock lock(lock_);
+  while (threads_waiting_to_advance_time_ != threads_.size())
+    ready_to_advance_time_.Wait();
+  thread_data->test_task_runner_->AdvanceMockTickClock(
+      next_time_ -
+      thread_data->test_task_runner_->GetMockTickClock()->NowTicks());
+  threads_ready_for_next_round_++;
+  if (threads_ready_for_next_round_ == threads_.size()) {
+    threads_waiting_to_advance_time_ = 0;
+    threads_ready_for_next_round_ = 0;
+    all_threads_ready_ = true;
+    next_time_ = TimeTicks::Max();
+    ready_for_next_round_.Broadcast();
+  }
+}
+
+void ThreadPoolManager::StartInitialThreads() {
+  {
+    AutoLock lock(lock_);
+    initial_threads_created_ = true;
+  }
+  ready_to_execute_threads_.Broadcast();
+}
+
+void ThreadPoolManager::WaitForAllThreads() {
+  if (threads_.empty())
+    return;
+  AutoLock lock(lock_);
+  while (threads_ready_to_terminate_ != threads_.size())
+    ready_to_terminate_.Wait();
+}
+
+void ThreadPoolManager::ThreadDone() {
+  AutoLock lock(lock_);
+  threads_ready_to_terminate_++;
+  if (threads_ready_to_terminate_ == threads_.size()) {
+    // Only the main thread waits for this event.
+    ready_to_terminate_.Signal();
+  }
+}
+
+const std::vector<std::unique_ptr<SimpleThreadImpl>>&
+ThreadPoolManager::threads() {
+  return threads_;
+}
+
+}  // namespace sequence_manager
+}  // namespace base

third_party/blink/renderer/platform/scheduler/base/thread_pool_manager.h

+// Copyright 2018 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
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_THREAD_POOL_MANAGER_H_
+#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_SCHEDULER_BASE_THREAD_POOL_MANAGER_H_
+
+#include <memory>
+#include <vector>
+
+#include "base/synchronization/condition_variable.h"
+#include "base/synchronization/lock.h"
+#include "base/time/time.h"
+#include "third_party/blink/renderer/platform/platform_export.h"
+#include "third_party/blink/renderer/platform/scheduler/base/proto/sequence_manager_test_description.pb.h"
+
+namespace base {
+namespace sequence_manager {
+
+class SequenceManagerFuzzerProcessor;
+class SimpleThreadImpl;
+class ThreadData;
+
+// Used by the SequenceManagerFuzzerProcessor to manage threads and synchronize
+// their clocks.
+class PLATFORM_EXPORT ThreadPoolManager {
+ public:
+  explicit ThreadPoolManager(SequenceManagerFuzzerProcessor* processor);
+  ~ThreadPoolManager();
+
+  // |time| is the virtual time in which the thread is created. The virtual time
+  // is controlled by |this| and synchronized for all the threads it owns.
+  void CreateThread(
+      const google::protobuf::RepeatedPtrField<
+          SequenceManagerTestDescription::Action>& initial_thread_actions,
+      TimeTicks time);
+
+  // Advances the mock tick clock of all the threads synchronously.
+  // Note that this doesn't guarantee advancing the thread's clock to |time|.
+  // The clock is advanced to the minimum desired time of all the owned threads.
+  void AdvanceClockSynchronouslyToTime(ThreadData* thread_data, TimeTicks time);
+
+  // Advances the mock tick clock of all the threads synchronously.
+  // Note that this doesn't guarantee advancing the thread's clock by the next
+  // pending task delay. The clock is advanced to the minimum desired time of
+  // all the owned threads.
+  void AdvanceClockSynchronouslyByPendingTaskDelay(ThreadData* thread_data);
+
+  // Used by a thread to notify the thread manager that it is done executing the
+  // thread actions passed to ThreadPoolManager::CreateThread.
+  void ThreadDone();
+
+  void StartInitialThreads();
+
+  // Used by the processor to wait for all of the threads to finish executing
+  // the actions passed by ThreadPoolManager::CreateThread. Note that
+  // the threads are not terminated until |this| gets destructed.
+  void WaitForAllThreads();
+
+  const std::vector<std::unique_ptr<SimpleThreadImpl>>& threads();
+
+ private:
+  void StartThread(
+      const google::protobuf::RepeatedPtrField<
+          SequenceManagerTestDescription::Action>& initial_thread_actions,
+      ThreadData* thread_data);
+
+  // Helper function used by AdvanceClockSynchronouslyToTime and
+  // AdvanceClockSynchronouslyByPendingTaskDelay to notify the manager when all
+  // threads are ready to compute their next desired time.
+  void ThreadReadyToComputeTime();
+
+  // Helper function used by AdvanceClockSynchronouslyToTime and
+  // AdvanceClockSynchronouslyByPendingTaskDelay to advance the thread's clock
+  // to |next_time_|. Note that this function waits until all owned threads have
+  // voted on the value of |next_time_|.
+  void AdvanceThreadClock(ThreadData* thread_data);
+
+  // Owner of this class.
+  SequenceManagerFuzzerProcessor* const processor_;
+
+  // Used to protect all the members below.
+  Lock lock_;
+
+  // Used to synchronize virtual time across all threads.
+  TimeTicks next_time_;
+
+  // Condition to ensure that all threads have their desired next time
+  // computed, and thus the global |next_time_| can be computed as their
+  // minimum value.
+  ConditionVariable ready_to_compute_time_;
+
+  // Condition that |next_time_| is computed and that all threads can advance
+  // their clock to |next_time_|.
+  ConditionVariable ready_to_advance_time_;
+
+  // Condition that all threads are done and the program is ready to
+  // terminate.
+  ConditionVariable ready_to_terminate_;
+
+  // Condition that threads can start running. This is needed to make sure all
+  // of the initial (program entry points) threads were created before any
+  // thread starts running.
+  ConditionVariable ready_to_execute_threads_;
+
+  // A round starts by all of the threads waiting to compute their desired
+  // next time and ends by all of them advancing their clocks.
+  ConditionVariable ready_for_next_round_;
+
+  uint64_t threads_waiting_to_compute_time_;
+  uint64_t threads_waiting_to_advance_time_;
+
+  // Number of threads done advancing their clocks and are ready for the next
+  // round.
+  uint64_t threads_ready_for_next_round_;
+
+  // Number of threads done executing their sequence of actions.
+  uint64_t threads_ready_to_terminate_;
+
+  // Used to notify the condition |ready_for_next_round_|.
+  bool all_threads_ready_;
+
+  // Used to notify the condition |ready_to_start_threads_|.
+  bool initial_threads_created_;
+
+  // Threads that are being managed/synchronized. For unit testing purposes,
+  // make sure not to create threads at the same time (if the ordering matters)
+  // since in this case the order will not be deterministic.
+  std::vector<std::unique_ptr<SimpleThreadImpl>> threads_;
+};
+
+}  // namespace sequence_manager
+}  // namespace base
+
+#endif