TaskScheduler [4/9] Priority Queue

base/task_scheduler/priority_queue.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/priority_queue.h"
+
+#include <utility>
+
+#include "base/logging.h"
+
+namespace base {
+namespace internal {
+
+PriorityQueue::SequenceAndSortKey::SequenceAndSortKey()
+    : sort_key(TaskPriority::LOWEST, TimeTicks()) {}
+
+PriorityQueue::SequenceAndSortKey::SequenceAndSortKey(
+    scoped_refptr<Sequence> sequence,
+    const SequenceSortKey& sort_key)
+    : sequence(std::move(sequence)), sort_key(sort_key) {}
+
+PriorityQueue::SequenceAndSortKey::~SequenceAndSortKey() = default;
+
+PriorityQueue::Transaction::Transaction(PriorityQueue* outer_queue)
+    : outer_queue_(outer_queue),
+      auto_lock_(new AutoSchedulerLock(outer_queue_->container_lock_)) {
+  DCHECK(CalledOnValidThread());
+}
+
+PriorityQueue::Transaction::~Transaction() {
+  DCHECK(CalledOnValidThread());
+
+  // Run the sequence insertion callback once for each Sequence that was
+  // inserted in the PriorityQueue during the lifetime of this Transaction.
+  // Perform this outside the scope of PriorityQueue's lock to avoid imposing an
+  // unnecessary lock dependency on |sequence_inserted_callback_|'s destination.
+  auto_lock_.reset();
+  for (size_t i = 0; i < num_pushed_sequences_; ++i)
+    outer_queue_->sequence_inserted_callback_.Run();
+}
+
+void PriorityQueue::Transaction::Push(
+    scoped_ptr<SequenceAndSortKey> sequence_and_sort_key) {
+  DCHECK(CalledOnValidThread());
+  DCHECK(!sequence_and_sort_key->is_null());
+
+  outer_queue_->container_.push(std::move(sequence_and_sort_key));
+  ++num_pushed_sequences_;
+}
+
+const PriorityQueue::SequenceAndSortKey& PriorityQueue::Transaction::Peek()
+    const {
+  DCHECK(CalledOnValidThread());
+
+  if (outer_queue_->container_.empty())
+    return outer_queue_->empty_sequence_and_sort_key_;

[danakj, 2016/03/18 20:24:05]

Maybe consider an IsEmpty() instead of returning empty on Peek, and require Peek
to be non-empty? I think that would be nicer. This CL's gone on enough, so
perhaps a TODO and a followup?

[fdoray, 2016/03/18 21:22:18]

Done.

+
+  return *outer_queue_->container_.top();
+}
+
+void PriorityQueue::Transaction::Pop() {
+  DCHECK(CalledOnValidThread());
+  DCHECK(!outer_queue_->container_.empty());
+  outer_queue_->container_.pop();
+}
+
+PriorityQueue::PriorityQueue(const Closure& sequence_inserted_callback)
+    : sequence_inserted_callback_(sequence_inserted_callback) {
+  DCHECK(!sequence_inserted_callback_.is_null());
+}
+
+PriorityQueue::PriorityQueue(const Closure& sequence_inserted_callback,
+                             const PriorityQueue* predecessor_priority_queue)
+    : container_lock_(&predecessor_priority_queue->container_lock_),
+      sequence_inserted_callback_(sequence_inserted_callback) {
+  DCHECK(!sequence_inserted_callback_.is_null());
+  DCHECK(predecessor_priority_queue);
+}
+
+PriorityQueue::~PriorityQueue() = default;
+
+scoped_ptr<PriorityQueue::Transaction> PriorityQueue::BeginTransaction() {
+  return make_scoped_ptr(new Transaction(this));
+}
+
+}  // namespace internal
+}  // namespace base