Revert of Disallow posting tasks to SequencedWorkerPools by default.

base/threading/sequenced_worker_pool.cc

 // Copyright (c) 2012 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.
 
 #include "base/threading/sequenced_worker_pool.h"
 
 #include <stdint.h>
 
 #include <list>
 #include <map>
 #include <memory>
 #include <set>
 #include <unordered_map>
 #include <utility>
 #include <vector>
 
 #include "base/atomic_sequence_num.h"
+#include "base/atomicops.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/critical_closure.h"
-#include "base/debug/dump_without_crashing.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/stl_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/condition_variable.h"
 #include "base/synchronization/lock.h"
 #include "base/task_scheduler/post_task.h"
 #include "base/task_scheduler/task_scheduler.h"
@@ skipping 15 matching lines @@
 #endif
 
 #if !defined(OS_NACL)
 #include "base/metrics/histogram_macros.h"
 #endif
 
 namespace base {
 
 namespace {
 
-// An enum representing the state of all pools. A non-test process should only
-// ever transition from POST_TASK_DISABLED to one of the active states. A test
-// process may transition from one of the active states to POST_TASK_DISABLED
-// when DisableForProcessForTesting() is called.
+// An enum representing the state of all pools. Any given non-test process
+// should only ever transition from NONE_ACTIVE to one of the active states.
+// Transitions between actives states are unexpected. The
+// REDIRECTED_TO_TASK_SCHEDULER transition occurs when
+// RedirectToTaskSchedulerForProcess() is called. The WORKER_CREATED transition
+// occurs when a Worker needs to be created because the first task was posted
+// and the state is still NONE_ACTIVE. In a test process, a transition to
+// NONE_ACTIVE occurs when ResetRedirectToTaskSchedulerForProcessForTesting() is
+// called.
 //
-// External memory synchronization is required to call a method that reads
-// |g_all_pools_state| after calling a method that modifies it.
+// |g_all_pools_state| uses relaxed atomic operations to ensure no data race
+// between reads/writes, strict memory ordering isn't required per no other
+// state being inferred from its value. Explicit synchronization (e.g. locks or
+// events) would be overkill (it's fine for other threads to still see
+// NONE_ACTIVE after the first Worker was created -- this is not possible for
+// REDIRECTED_TO_TASK_SCHEDULER per its API requesting to be invoked while no
+// other threads are active).
 //
 // TODO(gab): Remove this if http://crbug.com/622400 fails (SequencedWorkerPool
 // will be phased out completely otherwise).
-enum class AllPoolsState {
-  POST_TASK_DISABLED,
-  USE_WORKER_POOL,
+enum AllPoolsState : subtle::Atomic32 {
+  NONE_ACTIVE,
+  WORKER_CREATED,
   REDIRECTED_TO_TASK_SCHEDULER,
 };
-AllPoolsState g_all_pools_state = AllPoolsState::POST_TASK_DISABLED;
+subtle::Atomic32 g_all_pools_state = AllPoolsState::NONE_ACTIVE;
 
 struct SequencedTask : public TrackingInfo  {
   SequencedTask()
       : sequence_token_id(0),
         trace_id(0),
         sequence_task_number(0),
         shutdown_behavior(SequencedWorkerPool::BLOCK_SHUTDOWN) {}
 
   explicit SequencedTask(const tracked_objects::Location& from_here)
       : base::TrackingInfo(from_here, TimeTicks()),
@@ skipping 482 matching lines @@
 // Worker definitions ---------------------------------------------------------
 
 SequencedWorkerPool::Worker::Worker(
     scoped_refptr<SequencedWorkerPool> worker_pool,
     int thread_number,
     const std::string& prefix)
     : SimpleThread(prefix + StringPrintf("Worker%d", thread_number)),
       worker_pool_(std::move(worker_pool)),
       task_shutdown_behavior_(BLOCK_SHUTDOWN),
       is_processing_task_(false) {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
   Start();
 }
 
 SequencedWorkerPool::Worker::~Worker() {
 }
 
 void SequencedWorkerPool::Worker::Run() {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
 #if defined(OS_WIN)
   win::ScopedCOMInitializer com_initializer;
 #endif
 
   // Store a pointer to this worker in thread local storage for static function
   // access.
   DCHECK(!lazy_tls_ptr_.Get().Get());
   lazy_tls_ptr_.Get().Set(this);
 
@@ skipping 78 matching lines @@
   return SequenceToken(LockedGetNamedTokenID(name));
 }
 
 bool SequencedWorkerPool::Inner::PostTask(
     const std::string* optional_token_name,
     SequenceToken sequence_token,
     WorkerShutdown shutdown_behavior,
     const tracked_objects::Location& from_here,
     const Closure& task,
     TimeDelta delay) {
-  // TODO(fdoray): Uncomment this DCHECK. It is initially commented to avoid a
-  // revert of the CL that adds debug::DumpWithoutCrashing() if it fails on the
-  // waterfall. https://crbug.com/622400
-  // DCHECK_NE(AllPoolsState::POST_TASK_DISABLED, g_all_pools_state);
-
-  if (g_all_pools_state == AllPoolsState::POST_TASK_DISABLED)
-    debug::DumpWithoutCrashing();
-
   DCHECK(delay.is_zero() || shutdown_behavior == SKIP_ON_SHUTDOWN);
   SequencedTask sequenced(from_here);
   sequenced.sequence_token_id = sequence_token.id_;
   sequenced.shutdown_behavior = shutdown_behavior;
   sequenced.posted_from = from_here;
   sequenced.task =
       shutdown_behavior == BLOCK_SHUTDOWN ?
       base::MakeCriticalClosure(task) : task;
   sequenced.time_to_run = TimeTicks::Now() + delay;
 
@@ skipping 29 matching lines @@
         "SequencedWorkerPool::Inner::PostTask",
         TRACE_ID_MANGLE(GetTaskTraceID(sequenced, static_cast<void*>(this))),
         TRACE_EVENT_FLAG_FLOW_OUT);
 
     sequenced.sequence_task_number = LockedGetNextSequenceTaskNumber();
 
     // Now that we have the lock, apply the named token rules.
     if (optional_token_name)
       sequenced.sequence_token_id = LockedGetNamedTokenID(*optional_token_name);
 
-    if (g_all_pools_state == AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+    if (subtle::NoBarrier_Load(&g_all_pools_state) ==
+        AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
       if (!PostTaskToTaskScheduler(sequenced, delay))
         return false;
     } else {
       pending_tasks_.insert(sequenced);
 
       if (sequenced.shutdown_behavior == BLOCK_SHUTDOWN)
         blocking_shutdown_pending_task_count_++;
 
       create_thread_id = PrepareToStartAdditionalThreadIfHelpful();
     }
   }
 
-  // Use != REDIRECTED_TO_TASK_SCHEDULER instead of == USE_WORKER_POOL to ensure
-  // correct behavior if a task is posted to a SequencedWorkerPool before
-  // Enable(WithRedirectionToTaskScheduler)ForProcess() in a non-DCHECK build.
-  if (g_all_pools_state != AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+  if (subtle::NoBarrier_Load(&g_all_pools_state) !=
+      AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
     // Actually start the additional thread or signal an existing one outside
     // the lock.
     if (create_thread_id)
       FinishStartingAdditionalThread(create_thread_id);
     else
       SignalHasWork();
   }
 
 #if DCHECK_IS_ON()
   {
     AutoLock lock_for_dcheck(lock_);
     // Some variables are exposed in both modes for convenience but only really
     // intended for one of them at runtime, confirm exclusive usage here.
-    if (g_all_pools_state == AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+    if (subtle::NoBarrier_Load(&g_all_pools_state) ==
+        AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
       DCHECK(pending_tasks_.empty());
       DCHECK_EQ(0, create_thread_id);
     } else {
       DCHECK(sequenced_task_runner_map_.empty());
     }
   }
 #endif  // DCHECK_IS_ON()
 
   return true;
 }
 
 bool SequencedWorkerPool::Inner::PostTaskToTaskScheduler(
     const SequencedTask& sequenced,
     const TimeDelta& delay) {
-  DCHECK_EQ(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
 
   // Confirm that the TaskScheduler's shutdown behaviors use the same
   // underlying values as SequencedWorkerPool.
   static_assert(
       static_cast<int>(TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN) ==
           static_cast<int>(CONTINUE_ON_SHUTDOWN),
       "TaskShutdownBehavior and WorkerShutdown enum mismatch for "
       "CONTINUE_ON_SHUTDOWN.");
@@ skipping 13 matching lines @@
                                 .WithPriority(task_priority_)
                                 .WithShutdownBehavior(task_shutdown_behavior);
   return GetTaskSchedulerTaskRunner(sequenced.sequence_token_id, traits)
       ->PostDelayedTask(sequenced.posted_from, sequenced.task, delay);
 }
 
 scoped_refptr<TaskRunner>
 SequencedWorkerPool::Inner::GetTaskSchedulerTaskRunner(
     int sequence_token_id,
     const TaskTraits& traits) {
-  DCHECK_EQ(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
 
   static_assert(
       static_cast<int>(TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN) == 0,
       "TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN must be equal to 0 to be "
       "used as an index in |unsequenced_task_runners_|.");
   static_assert(static_cast<int>(TaskShutdownBehavior::SKIP_ON_SHUTDOWN) == 1,
                 "TaskShutdownBehavior::SKIP_ON_SHUTDOWN must be equal to 1 to "
                 "be used as an index in |unsequenced_task_runners_|.");
@@ skipping 16 matching lines @@
     task_runner = sequence_token_id
                       ? CreateSequencedTaskRunnerWithTraits(traits)
                       : CreateTaskRunnerWithTraits(traits);
   }
 
   return task_runner;
 }
 
 bool SequencedWorkerPool::Inner::RunsTasksOnCurrentThread() const {
   AutoLock lock(lock_);
-  if (g_all_pools_state == AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+  if (subtle::NoBarrier_Load(&g_all_pools_state) ==
+      AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
     if (!runs_tasks_on_verifier_) {
       runs_tasks_on_verifier_ = CreateTaskRunnerWithTraits(
           TaskTraits().WithFileIO().WithPriority(task_priority_));
     }
     return runs_tasks_on_verifier_->RunsTasksOnCurrentThread();
   } else {
     return ContainsKey(threads_, PlatformThread::CurrentId());
   }
 }
 
 bool SequencedWorkerPool::Inner::IsRunningSequenceOnCurrentThread(
     SequenceToken sequence_token) const {
   DCHECK(sequence_token.IsValid());
 
   AutoLock lock(lock_);
 
-  if (g_all_pools_state == AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+  if (subtle::NoBarrier_Load(&g_all_pools_state) ==
+      AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
     const auto sequenced_task_runner_it =
         sequenced_task_runner_map_.find(sequence_token.id_);
     return sequenced_task_runner_it != sequenced_task_runner_map_.end() &&
            sequenced_task_runner_it->second->RunsTasksOnCurrentThread();
   } else {
     ThreadMap::const_iterator found =
         threads_.find(PlatformThread::CurrentId());
     return found != threads_.end() && found->second->is_processing_task() &&
            sequence_token.Equals(found->second->task_sequence_token());
   }
 }
 
 // See https://code.google.com/p/chromium/issues/detail?id=168415
 void SequencedWorkerPool::Inner::CleanupForTesting() {
-  DCHECK_NE(g_all_pools_state, AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER);
+  DCHECK_NE(subtle::NoBarrier_Load(&g_all_pools_state),
+            AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER);
   AutoLock lock(lock_);
   CHECK_EQ(CLEANUP_DONE, cleanup_state_);
   if (shutdown_called_)
     return;
   if (pending_tasks_.empty() && waiting_thread_count_ == threads_.size())
     return;
   cleanup_state_ = CLEANUP_REQUESTED;
   cleanup_idlers_ = 0;
   has_work_cv_.Signal();
   while (cleanup_state_ != CLEANUP_DONE)
@@ skipping 10 matching lines @@
   {
     AutoLock lock(lock_);
     // Cleanup and Shutdown should not be called concurrently.
     CHECK_EQ(CLEANUP_DONE, cleanup_state_);
     if (shutdown_called_)
       return;
     shutdown_called_ = true;
 
     max_blocking_tasks_after_shutdown_ = max_new_blocking_tasks_after_shutdown;
 
-    if (g_all_pools_state != AllPoolsState::USE_WORKER_POOL)
+    if (subtle::NoBarrier_Load(&g_all_pools_state) !=
+        AllPoolsState::WORKER_CREATED) {
       return;
+    }
 
     // Tickle the threads. This will wake up a waiting one so it will know that
     // it can exit, which in turn will wake up any other waiting ones.
     SignalHasWork();
 
     // There are no pending or running tasks blocking shutdown, we're done.
     if (CanShutdown())
       return;
   }
 
@@ skipping 18 matching lines @@
                       TimeTicks::Now() - shutdown_wait_begin);
 #endif
 }
 
 bool SequencedWorkerPool::Inner::IsShutdownInProgress() {
     AutoLock lock(lock_);
     return shutdown_called_;
 }
 
 void SequencedWorkerPool::Inner::ThreadLoop(Worker* this_worker) {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
   {
     AutoLock lock(lock_);
     DCHECK(thread_being_created_);
     thread_being_created_ = false;
     auto result = threads_.insert(
         std::make_pair(this_worker->tid(), WrapUnique(this_worker)));
     DCHECK(result.second);
 
     while (true) {
 #if defined(OS_MACOSX)
@@ skipping 111 matching lines @@
 
   // We noticed we should exit. Wake up the next worker so it knows it should
   // exit as well (because the Shutdown() code only signals once).
   SignalHasWork();
 
   // Possibly unblock shutdown.
   can_shutdown_cv_.Signal();
 }
 
 void SequencedWorkerPool::Inner::HandleCleanup() {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
   if (cleanup_state_ == CLEANUP_DONE)
     return;
   if (cleanup_state_ == CLEANUP_REQUESTED) {
     // We win, we get to do the cleanup as soon as the others wise up and idle.
     cleanup_state_ = CLEANUP_STARTING;
     while (thread_being_created_ ||
            cleanup_idlers_ != threads_.size() - 1) {
       has_work_cv_.Signal();
@@ skipping 46 matching lines @@
 int64_t SequencedWorkerPool::Inner::LockedGetNextSequenceTaskNumber() {
   lock_.AssertAcquired();
   // We assume that we never create enough tasks to wrap around.
   return next_sequence_task_number_++;
 }
 
 SequencedWorkerPool::Inner::GetWorkStatus SequencedWorkerPool::Inner::GetWork(
     SequencedTask* task,
     TimeDelta* wait_time,
     std::vector<Closure>* delete_these_outside_lock) {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
 
   // Find the next task with a sequence token that's not currently in use.
   // If the token is in use, that means another thread is running something
   // in that sequence, and we can't run it without going out-of-order.
   //
   // This algorithm is simple and fair, but inefficient in some cases. For
   // example, say somebody schedules 1000 slow tasks with the same sequence
   // number. We'll have to go through all those tasks each time we feel like
@@ skipping 67 matching lines @@
     }
 
     status = GET_WORK_FOUND;
     break;
   }
 
   return status;
 }
 
 int SequencedWorkerPool::Inner::WillRunWorkerTask(const SequencedTask& task) {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
 
   // Mark the task's sequence number as in use.
   if (task.sequence_token_id)
     current_sequences_.insert(task.sequence_token_id);
 
   // Ensure that threads running tasks posted with either SKIP_ON_SHUTDOWN
   // or BLOCK_SHUTDOWN will prevent shutdown until that task or thread
   // completes.
@@ skipping 12 matching lines @@
   // if there is one waiting to pick up the next task.
   //
   // Note that we really need to do this *before* running the task, not
   // after. Otherwise, if more than one task is posted, the creation of the
   // second thread (since we only create one at a time) will be blocked by
   // the execution of the first task, which could be arbitrarily long.
   return PrepareToStartAdditionalThreadIfHelpful();
 }
 
 void SequencedWorkerPool::Inner::DidRunWorkerTask(const SequencedTask& task) {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
 
   if (task.shutdown_behavior != CONTINUE_ON_SHUTDOWN) {
     DCHECK_GT(blocking_shutdown_thread_count_, 0u);
     blocking_shutdown_thread_count_--;
   }
 
   if (task.sequence_token_id)
     current_sequences_.erase(task.sequence_token_id);
 }
 
 bool SequencedWorkerPool::Inner::IsSequenceTokenRunnable(
     int sequence_token_id) const {
-  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER, g_all_pools_state);
+  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
   return !sequence_token_id ||
       current_sequences_.find(sequence_token_id) ==
           current_sequences_.end();
 }
 
 int SequencedWorkerPool::Inner::PrepareToStartAdditionalThreadIfHelpful() {
-  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER, g_all_pools_state);
+  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   lock_.AssertAcquired();
   // How thread creation works:
   //
   // We'de like to avoid creating threads with the lock held. However, we
   // need to be sure that we have an accurate accounting of the threads for
   // proper Joining and deltion on shutdown.
   //
   // We need to figure out if we need another thread with the lock held, which
   // is what this function does. It then marks us as in the process of creating
@@ skipping 31 matching lines @@
         thread_being_created_ = true;
         return static_cast<int>(threads_.size() + 1);
       }
     }
   }
   return 0;
 }
 
 void SequencedWorkerPool::Inner::FinishStartingAdditionalThread(
     int thread_number) {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   // Called outside of the lock.
   DCHECK_GT(thread_number, 0);
 
+  if (subtle::NoBarrier_Load(&g_all_pools_state) !=
+      AllPoolsState::WORKER_CREATED) {
+    DCHECK_EQ(AllPoolsState::NONE_ACTIVE,
+              subtle::NoBarrier_Load(&g_all_pools_state));
+    subtle::NoBarrier_Store(&g_all_pools_state, AllPoolsState::WORKER_CREATED);
+  }
+
   // The worker is assigned to the list when the thread actually starts, which
   // will manage the memory of the pointer.
   new Worker(worker_pool_, thread_number, thread_name_prefix_);
 }
 
 void SequencedWorkerPool::Inner::SignalHasWork() {
-  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER, g_all_pools_state);
+  DCHECK_NE(AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER,
+            subtle::NoBarrier_Load(&g_all_pools_state));
 
   has_work_cv_.Signal();
   if (testing_observer_) {
     testing_observer_->OnHasWork();
   }
 }
 
 bool SequencedWorkerPool::Inner::CanShutdown() const {
-  DCHECK_EQ(AllPoolsState::USE_WORKER_POOL, g_all_pools_state);
+  DCHECK_EQ(AllPoolsState::WORKER_CREATED,
+            subtle::NoBarrier_Load(&g_all_pools_state));
   lock_.AssertAcquired();
   // See PrepareToStartAdditionalThreadIfHelpful for how thread creation works.
   return !thread_being_created_ &&
          blocking_shutdown_thread_count_ == 0 &&
          blocking_shutdown_pending_task_count_ == 0;
 }
 
 base::StaticAtomicSequenceNumber
 SequencedWorkerPool::Inner::g_last_sequence_number_;
 
@@ skipping 17 matching lines @@
 scoped_refptr<SequencedWorkerPool>
 SequencedWorkerPool::GetWorkerPoolForCurrentThread() {
   Worker* worker = Worker::GetForCurrentThread();
   if (!worker)
     return nullptr;
 
   return worker->worker_pool();
 }
 
 // static
-void SequencedWorkerPool::EnableForProcess() {
-  DCHECK_EQ(AllPoolsState::POST_TASK_DISABLED, g_all_pools_state);
-  g_all_pools_state = AllPoolsState::USE_WORKER_POOL;
+void SequencedWorkerPool::RedirectToTaskSchedulerForProcess() {
+  DCHECK(TaskScheduler::GetInstance());
+  // Hitting this DCHECK indicates that a task was posted to a
+  // SequencedWorkerPool before the TaskScheduler was initialized and
+  // redirected, posting task to SequencedWorkerPools needs to at least be
+  // delayed until after that point.
+  DCHECK_EQ(AllPoolsState::NONE_ACTIVE,
+            subtle::NoBarrier_Load(&g_all_pools_state));
+  subtle::NoBarrier_Store(&g_all_pools_state,
+                          AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER);
 }
 
 // static
-void SequencedWorkerPool::EnableWithRedirectionToTaskSchedulerForProcess() {
-  DCHECK_EQ(AllPoolsState::POST_TASK_DISABLED, g_all_pools_state);
-  DCHECK(TaskScheduler::GetInstance());
-  g_all_pools_state = AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER;
-}
-
-// static
-void SequencedWorkerPool::DisableForProcessForTesting() {
-  g_all_pools_state = AllPoolsState::POST_TASK_DISABLED;
-}
-
-// static
-bool SequencedWorkerPool::IsEnabled() {
-  return g_all_pools_state != AllPoolsState::POST_TASK_DISABLED;
+void SequencedWorkerPool::ResetRedirectToTaskSchedulerForProcessForTesting() {
+  // This can be called when the current state is REDIRECTED_TO_TASK_SCHEDULER
+  // to stop redirecting tasks. It can also be called when the current state is
+  // WORKER_CREATED to allow RedirectToTaskSchedulerForProcess() to be called
+  // (RedirectToTaskSchedulerForProcess() cannot be called after a worker has
+  // been created if this isn't called).
+  subtle::NoBarrier_Store(&g_all_pools_state, AllPoolsState::NONE_ACTIVE);
 }
 
 SequencedWorkerPool::SequencedWorkerPool(size_t max_threads,
                                          const std::string& thread_name_prefix,
                                          base::TaskPriority task_priority)
     : constructor_task_runner_(SequencedTaskRunnerHandle::Get()),
       inner_(new Inner(this,
                        max_threads,
                        thread_name_prefix,
                        task_priority,
@@ skipping 118 matching lines @@
   return PostDelayedWorkerTask(from_here, task, delay);
 }
 
 bool SequencedWorkerPool::RunsTasksOnCurrentThread() const {
   return inner_->RunsTasksOnCurrentThread();
 }
 
 void SequencedWorkerPool::FlushForTesting() {
   DCHECK(!RunsTasksOnCurrentThread());
   base::ThreadRestrictions::ScopedAllowWait allow_wait;
-  if (g_all_pools_state == AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
+  if (subtle::NoBarrier_Load(&g_all_pools_state) ==
+      AllPoolsState::REDIRECTED_TO_TASK_SCHEDULER) {
     // TODO(gab): Remove this if http://crbug.com/622400 fails.
     TaskScheduler::GetInstance()->FlushForTesting();
   } else {
     inner_->CleanupForTesting();
   }
 }
 
 void SequencedWorkerPool::SignalHasWorkForTesting() {
   inner_->SignalHasWorkForTesting();
 }
 
 void SequencedWorkerPool::Shutdown(int max_new_blocking_tasks_after_shutdown) {
   DCHECK(constructor_task_runner_->RunsTasksOnCurrentThread());
   inner_->Shutdown(max_new_blocking_tasks_after_shutdown);
 }
 
 bool SequencedWorkerPool::IsShutdownInProgress() {
   return inner_->IsShutdownInProgress();
 }
 
 bool SequencedWorkerPool::IsRunningSequenceOnCurrentThread(
     SequenceToken sequence_token) const {
   return inner_->IsRunningSequenceOnCurrentThread(sequence_token);
 }
 
 }  // namespace base