1 // Copyright 2016 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_ 6 #define BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_ 7 8 #include "base/base_export.h" 9 #include "base/callback_helpers.h" 10 #include "base/macros.h" 11 #include "base/memory/ref_counted.h" 12 #include "base/single_thread_task_runner.h" 13 14 namespace base { 15 16 // ThreadTaskRunnerHandle stores a reference to a thread's TaskRunner 17 // in thread-local storage. Callers can then retrieve the TaskRunner 18 // for the current thread by calling ThreadTaskRunnerHandle::Get(). 19 // At most one TaskRunner may be bound to each thread at a time. 20 // Prefer SequenceTaskRunnerHandle to this unless thread affinity is required. 21 class BASE_EXPORT ThreadTaskRunnerHandle { 22 public: 23 // Gets the SingleThreadTaskRunner for the current thread. 24 static scoped_refptr<SingleThreadTaskRunner> Get(); 25 26 // Returns true if the SingleThreadTaskRunner is already created for 27 // the current thread. 28 static bool IsSet(); 29 30 // Overrides ThreadTaskRunnerHandle::Get()'s |task_runner_| to point at 31 // |overriding_task_runner| until the returned ScopedClosureRunner goes out of 32 // scope (instantiates a ThreadTaskRunnerHandle for that scope if |!IsSet()|). 33 // Nested overrides are allowed but callers must ensure the 34 // ScopedClosureRunners expire in LIFO (stack) order. Note: nesting 35 // ThreadTaskRunnerHandles isn't generally desired but it's useful in unit 36 // tests where multiple task runners can share the main thread for simplicity 37 // and determinism. 38 static ScopedClosureRunner OverrideForTesting( 39 scoped_refptr<SingleThreadTaskRunner> overriding_task_runner); 40 41 // Binds |task_runner| to the current thread. |task_runner| must belong 42 // to the current thread for this to succeed. 43 explicit ThreadTaskRunnerHandle( 44 scoped_refptr<SingleThreadTaskRunner> task_runner); 45 ~ThreadTaskRunnerHandle(); 46 47 private: 48 scoped_refptr<SingleThreadTaskRunner> task_runner_; 49 50 DISALLOW_COPY_AND_ASSIGN(ThreadTaskRunnerHandle); 51 }; 52 53 } // namespace base 54 55 #endif // BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_ 56