TaskScheduler [5/9] Task Tracker

base/task_scheduler/task_tracker.cc

+// Copyright 2016 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/task_scheduler/task_tracker.h"
+
+#include "base/callback.h"
+#include "base/debug/task_annotator.h"
+
+namespace base {
+namespace internal {
+
+namespace {
+const char kQueueFunctionName[] = "base::PostTask";
+}  // namespace
+
+TaskTracker::TaskTracker()
+    : cv_(lock_.CreateConditionVariable()),

[gab, 2016/03/17 01:42:12]

Since we only need |cv_| during shutdown. How about we only set it then and then
use |cv_|'s existence as an indicator of |is_shutting_down| (i.e. getting rid of
that boolean).

And probably rename |cv_| to |shutdown_cv_| now that this class is about more
than just shutdown (especially if using it to replace |is_shutting_down|).

[fdoray, 2016/03/17 20:12:16]

Done.

+      num_tasks_blocking_shutdown_(0),
+      is_shutting_down_(false),
+      shutdown_completed_(false) {}
+
+TaskTracker::~TaskTracker() = default;
+
+void TaskTracker::Shutdown() {
+  AutoSchedulerLock auto_lock(lock_);
+
+  DCHECK(!shutdown_completed_ && !is_shutting_down_)
+      << "TaskTracker::Shutdown() should only be invoked once.";
+  is_shutting_down_ = true;
+
+  // Wait until the number of tasks blocking shutdown is zero.
+  while (num_tasks_blocking_shutdown_ != 0)
+    cv_->Wait();
+
+  is_shutting_down_ = false;
+  shutdown_completed_ = true;
+}
+
+void TaskTracker::PostTask(
+    const Callback<void(scoped_ptr<Task>)>& post_task_callback,
+    scoped_ptr<Task> task) {
+  DCHECK(!post_task_callback.is_null());
+  DCHECK(task.get());

[gab, 2016/03/17 01:42:12]

I don't think .get() is necessary here, scoped_ptr implements operator(bool)
IIRC.

[fdoray, 2016/03/17 20:12:16]

Done.

+
+  if (!BeforePostTask(task->traits.shutdown_behavior()))
+    return;
+
+  debug::TaskAnnotator task_annotator;
+  task_annotator.DidQueueTask(kQueueFunctionName, *task.get());
+
+  post_task_callback.Run(std::move(task));
+}
+
+void TaskTracker::RunTask(const Task* task) {
+  DCHECK(task);
+
+  const TaskShutdownBehavior shutdown_behavior =
+      task->traits.shutdown_behavior();
+  if (!BeforeRunTask(shutdown_behavior))
+    return;
+
+  debug::TaskAnnotator task_annotator;
+  task_annotator.RunTask(kQueueFunctionName, *task);
+
+  AfterRunTask(shutdown_behavior);
+}
+
+bool TaskTracker::BeforePostTask(TaskShutdownBehavior shutdown_behavior) {
+  AutoSchedulerLock auto_lock(lock_);
+
+  if (shutdown_completed_)
+    return false;
+
+  if (shutdown_behavior == TaskShutdownBehavior::BLOCK_SHUTDOWN) {
+    // BLOCK_SHUTDOWN tasks block shutdown between the moment they are posted
+    // and the moment they complete their execution.
+    ++num_tasks_blocking_shutdown_;
+    return true;
+  }
+
+  return !is_shutting_down_;
+}
+
+bool TaskTracker::BeforeRunTask(TaskShutdownBehavior shutdown_behavior) {
+  AutoSchedulerLock auto_lock(lock_);
+
+  if (shutdown_completed_) {
+    DCHECK_NE(TaskShutdownBehavior::BLOCK_SHUTDOWN, shutdown_behavior);

[gab, 2016/03/17 01:42:12]

Add a comment like:

// A BLOCK_SHUTDOWN task posted after shutdown has completed is an ordering bug.
This DCHECK aims to catch those early.

[fdoray, 2016/03/17 20:12:16]

Done.

+    return false;
+  }
+
+  switch (shutdown_behavior) {
+    case TaskShutdownBehavior::BLOCK_SHUTDOWN:
+      return true;
+
+    case TaskShutdownBehavior::SKIP_ON_SHUTDOWN:
+      if (is_shutting_down_)
+        return false;
+
+      // SKIP_ON_SHUTDOWN tasks block shutdown while they are running.
+      ++num_tasks_blocking_shutdown_;
+      return true;
+
+    case TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN:
+      return !is_shutting_down_;
+  }
+
+  NOTREACHED();
+  return false;
+}
+
+void TaskTracker::AfterRunTask(TaskShutdownBehavior shutdown_behavior) {
+  if (shutdown_behavior == TaskShutdownBehavior::BLOCK_SHUTDOWN ||
+      shutdown_behavior == TaskShutdownBehavior::SKIP_ON_SHUTDOWN) {
+    AutoSchedulerLock auto_lock(lock_);
+    DCHECK_GT(num_tasks_blocking_shutdown_, 0U);
+    --num_tasks_blocking_shutdown_;
+    if (num_tasks_blocking_shutdown_ == 0 && is_shutting_down_)
+      cv_->Signal();
+  }
+}
+
+}  // namespace internal
+}  // namespace base