Repo created

TMessagesProj/jni/voip/webrtc/base/task/thread_pool/sequence.h

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+// 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.
+
+#ifndef BASE_TASK_THREAD_POOL_SEQUENCE_H_
+#define BASE_TASK_THREAD_POOL_SEQUENCE_H_
+
+#include <stddef.h>
+
+#include "base/base_export.h"
+#include "base/compiler_specific.h"
+#include "base/containers/queue.h"
+#include "base/macros.h"
+#include "base/optional.h"
+#include "base/sequence_token.h"
+#include "base/task/task_traits.h"
+#include "base/task/thread_pool/pooled_parallel_task_runner.h"
+#include "base/task/thread_pool/sequence_sort_key.h"
+#include "base/task/thread_pool/task.h"
+#include "base/task/thread_pool/task_source.h"
+#include "base/threading/sequence_local_storage_map.h"
+
+namespace base {
+namespace internal {
+
+// A Sequence holds slots each containing up to a single Task that must be
+// executed in posting order.
+//
+// In comments below, an "empty Sequence" is a Sequence with no slot.
+//
+// Note: there is a known refcounted-ownership cycle in the Scheduler
+// architecture: Sequence -> Task -> TaskRunner -> Sequence -> ...
+// This is okay so long as the other owners of Sequence (PriorityQueue and
+// WorkerThread in alternation and
+// ThreadGroupImpl::WorkerThreadDelegateImpl::GetWork()
+// temporarily) keep running it (and taking Tasks from it as a result). A
+// dangling reference cycle would only occur should they release their reference
+// to it while it's not empty. In other words, it is only correct for them to
+// release it after PopTask() returns false to indicate it was made empty by
+// that call (in which case the next PushTask() will return true to indicate to
+// the caller that the Sequence should be re-enqueued for execution).
+//
+// This class is thread-safe.
+class BASE_EXPORT Sequence : public TaskSource {
+ public:
+  // A Transaction can perform multiple operations atomically on a
+  // Sequence. While a Transaction is alive, it is guaranteed that nothing
+  // else will access the Sequence; the Sequence's lock is held for the
+  // lifetime of the Transaction.
+  class BASE_EXPORT Transaction : public TaskSource::Transaction {
+   public:
+    Transaction(Transaction&& other);
+    ~Transaction();
+
+    // Returns true if the sequence would need to be queued after receiving a
+    // new Task.
+    bool WillPushTask() const WARN_UNUSED_RESULT;
+
+    // Adds |task| in a new slot at the end of the Sequence. This must only be
+    // called after invoking WillPushTask().
+    void PushTask(Task task);
+
+    Sequence* sequence() const { return static_cast<Sequence*>(task_source()); }
+
+   private:
+    friend class Sequence;
+
+    explicit Transaction(Sequence* sequence);
+
+    DISALLOW_COPY_AND_ASSIGN(Transaction);
+  };
+
+  // |traits| is metadata that applies to all Tasks in the Sequence.
+  // |task_runner| is a reference to the TaskRunner feeding this TaskSource.
+  // |task_runner| can be nullptr only for tasks with no TaskRunner, in which
+  // case |execution_mode| must be kParallel. Otherwise, |execution_mode| is the
+  // execution mode of |task_runner|.
+  Sequence(const TaskTraits& traits,
+           TaskRunner* task_runner,
+           TaskSourceExecutionMode execution_mode);
+
+  // Begins a Transaction. This method cannot be called on a thread which has an
+  // active Sequence::Transaction.
+  Transaction BeginTransaction() WARN_UNUSED_RESULT;
+
+  // TaskSource:
+  ExecutionEnvironment GetExecutionEnvironment() override;
+  size_t GetRemainingConcurrency() const override;
+
+  // Returns a token that uniquely identifies this Sequence.
+  const SequenceToken& token() const { return token_; }
+
+  SequenceLocalStorageMap* sequence_local_storage() {
+    return &sequence_local_storage_;
+  }
+
+ private:
+  ~Sequence() override;
+
+  // TaskSource:
+  RunStatus WillRunTask() override;
+  Task TakeTask(TaskSource::Transaction* transaction) override;
+  Task Clear(TaskSource::Transaction* transaction) override;
+  bool DidProcessTask(TaskSource::Transaction* transaction) override;
+  SequenceSortKey GetSortKey() const override;
+
+  // Releases reference to TaskRunner.
+  void ReleaseTaskRunner();
+
+  const SequenceToken token_ = SequenceToken::Create();
+
+  // Queue of tasks to execute.
+  base::queue<Task> queue_;
+
+  // True if a worker is currently associated with a Task from this Sequence.
+  bool has_worker_ = false;
+
+  // Holds data stored through the SequenceLocalStorageSlot API.
+  SequenceLocalStorageMap sequence_local_storage_;
+
+  DISALLOW_COPY_AND_ASSIGN(Sequence);
+};
+
+}  // namespace internal
+}  // namespace base
+
+#endif  // BASE_TASK_THREAD_POOL_SEQUENCE_H_