// Copyright 2016 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_
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#define BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_
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#include "base/base_export.h"
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#include "base/callback_helpers.h"
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#include "base/compiler_specific.h"
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#include "base/macros.h"
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#include "base/memory/ref_counted.h"
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#include "base/single_thread_task_runner.h"
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namespace base {
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// ThreadTaskRunnerHandle stores a reference to a thread's TaskRunner
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// in thread-local storage. Callers can then retrieve the TaskRunner
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// for the current thread by calling ThreadTaskRunnerHandle::Get().
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// At most one TaskRunner may be bound to each thread at a time.
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// Prefer SequencedTaskRunnerHandle to this unless thread affinity is required.
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class BASE_EXPORT ThreadTaskRunnerHandle {
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public:
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// Gets the SingleThreadTaskRunner for the current thread.
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static scoped_refptr<SingleThreadTaskRunner> Get();
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// Returns true if the SingleThreadTaskRunner is already created for
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// the current thread.
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static bool IsSet();
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// Overrides ThreadTaskRunnerHandle::Get()'s |task_runner_| to point at
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// |overriding_task_runner| until the returned ScopedClosureRunner goes out of
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// scope (instantiates a ThreadTaskRunnerHandle for that scope if |!IsSet()|).
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// Nested overrides are allowed but callers must ensure the
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// ScopedClosureRunners expire in LIFO (stack) order. Note: nesting
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// ThreadTaskRunnerHandles isn't generally desired but it's useful in unit
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// tests where multiple task runners can share the main thread for simplicity
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// and determinism.
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static ScopedClosureRunner OverrideForTesting(
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scoped_refptr<SingleThreadTaskRunner> overriding_task_runner)
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WARN_UNUSED_RESULT;
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// Binds |task_runner| to the current thread. |task_runner| must belong
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// to the current thread for this to succeed.
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explicit ThreadTaskRunnerHandle(
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scoped_refptr<SingleThreadTaskRunner> task_runner);
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~ThreadTaskRunnerHandle();
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private:
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scoped_refptr<SingleThreadTaskRunner> task_runner_;
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DISALLOW_COPY_AND_ASSIGN(ThreadTaskRunnerHandle);
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};
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} // namespace base
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#endif // BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_
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