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/compiler_specific.h" 11 #include "base/macros.h" 12 #include "base/memory/ref_counted.h" 13 #include "base/single_thread_task_runner.h" 14 15 namespace base { 16 17 // ThreadTaskRunnerHandle stores a reference to a thread's TaskRunner 18 // in thread-local storage. Callers can then retrieve the TaskRunner 19 // for the current thread by calling ThreadTaskRunnerHandle::Get(). 20 // At most one TaskRunner may be bound to each thread at a time. 21 // Prefer SequencedTaskRunnerHandle to this unless thread affinity is required. 22 class BASE_EXPORT ThreadTaskRunnerHandle { 23 public: 24 // Gets the SingleThreadTaskRunner for the current thread. 25 static scoped_refptr<SingleThreadTaskRunner> Get(); 26 27 // Returns true if the SingleThreadTaskRunner is already created for 28 // the current thread. 29 static bool IsSet(); 30 31 // Overrides ThreadTaskRunnerHandle::Get()'s |task_runner_| to point at 32 // |overriding_task_runner| until the returned ScopedClosureRunner goes out of 33 // scope (instantiates a ThreadTaskRunnerHandle for that scope if |!IsSet()|). 34 // Nested overrides are allowed but callers must ensure the 35 // ScopedClosureRunners expire in LIFO (stack) order. Note: nesting 36 // ThreadTaskRunnerHandles isn't generally desired but it's useful in unit 37 // tests where multiple task runners can share the main thread for simplicity 38 // and determinism. 39 static ScopedClosureRunner OverrideForTesting( 40 scoped_refptr<SingleThreadTaskRunner> overriding_task_runner) 41 WARN_UNUSED_RESULT; 42 43 // Binds |task_runner| to the current thread. |task_runner| must belong 44 // to the current thread for this to succeed. 45 explicit ThreadTaskRunnerHandle( 46 scoped_refptr<SingleThreadTaskRunner> task_runner); 47 ~ThreadTaskRunnerHandle(); 48 49 private: 50 scoped_refptr<SingleThreadTaskRunner> task_runner_; 51 52 DISALLOW_COPY_AND_ASSIGN(ThreadTaskRunnerHandle); 53 }; 54 55 } // namespace base 56 57 #endif // BASE_THREADING_THREAD_TASK_RUNNER_HANDLE_H_ 58