1 // Copyright 2019 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 PLATFORM_API_TASK_RUNNER_H_ 6 #define PLATFORM_API_TASK_RUNNER_H_ 7 8 #include <future> 9 #include <utility> 10 11 #include "platform/api/time.h" 12 13 namespace openscreen { 14 15 // A thread-safe API surface that allows for posting tasks. The underlying 16 // implementation may be single or multi-threaded, and all complication should 17 // be handled by the implementation class. The implementation must guarantee: 18 // (1) Tasks shall not overlap in time/CPU. 19 // (2) Tasks shall run sequentially, e.g. posting task A then B implies 20 // that A shall run before B. 21 // (3) If task A is posted before task B, then any mutation in A happens-before 22 // B runs (even if A and B run on different threads). 23 class TaskRunner { 24 public: 25 // Seem to get an error using clang when compiling with -fno-exceptions: 26 // error: implicit instantiation of undefined template 'std::__1::packaged_task<void () noexcept>' 27 #if __has_feature(cxx_exceptions) 28 using Task = std::packaged_task<void() noexcept>; 29 #else 30 using Task = std::packaged_task<void()>; 31 #endif 32 33 virtual ~TaskRunner() = default; 34 35 // Takes any callable target (function, lambda-expression, std::bind result, 36 // etc.) that should be run at the first convenient time. 37 template <typename Functor> PostTask(Functor f)38 inline void PostTask(Functor f) { 39 PostPackagedTask(Task(std::move(f))); 40 } 41 42 // Takes any callable target (function, lambda-expression, std::bind result, 43 // etc.) that should be run no sooner than |delay| time from now. Note that 44 // the Task might run after an additional delay, especially under heavier 45 // system load. There is no deadline concept. 46 template <typename Functor> PostTaskWithDelay(Functor f,Clock::duration delay)47 inline void PostTaskWithDelay(Functor f, Clock::duration delay) { 48 PostPackagedTaskWithDelay(Task(std::move(f)), delay); 49 } 50 51 // Implementations should provide the behavior explained in the comments above 52 // for PostTask[WithDelay](). Client code may also call these directly when 53 // passing an existing Task object. 54 virtual void PostPackagedTask(Task task) = 0; 55 virtual void PostPackagedTaskWithDelay(Task task, Clock::duration delay) = 0; 56 57 // Return true if the calling thread is the thread that task runner is using 58 // to run tasks, false otherwise. 59 virtual bool IsRunningOnTaskRunner() = 0; 60 }; 61 62 } // namespace openscreen 63 64 #endif // PLATFORM_API_TASK_RUNNER_H_ 65