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// Copyright 2019 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 PLATFORM_API_TASK_RUNNER_H_
#define PLATFORM_API_TASK_RUNNER_H_
#include <future>
#include <utility>
#include "platform/api/time.h"
namespace openscreen {
// A thread-safe API surface that allows for posting tasks. The underlying
// implementation may be single or multi-threaded, and all complication should
// be handled by the implementation class. The implementation must guarantee:
// (1) Tasks shall not overlap in time/CPU.
// (2) Tasks shall run sequentially, e.g. posting task A then B implies
// that A shall run before B.
// (3) If task A is posted before task B, then any mutation in A happens-before
// B runs (even if A and B run on different threads).
class TaskRunner {
public:
// Seem to get an error using clang when compiling with -fno-exceptions:
// error: implicit instantiation of undefined template 'std::__1::packaged_task<void () noexcept>'
#if __has_feature(cxx_exceptions)
using Task = std::packaged_task<void() noexcept>;
#else
using Task = std::packaged_task<void()>;
#endif
virtual ~TaskRunner() = default;
// Takes any callable target (function, lambda-expression, std::bind result,
// etc.) that should be run at the first convenient time.
template <typename Functor>
inline void PostTask(Functor f) {
PostPackagedTask(Task(std::move(f)));
}
// Takes any callable target (function, lambda-expression, std::bind result,
// etc.) that should be run no sooner than |delay| time from now. Note that
// the Task might run after an additional delay, especially under heavier
// system load. There is no deadline concept.
template <typename Functor>
inline void PostTaskWithDelay(Functor f, Clock::duration delay) {
PostPackagedTaskWithDelay(Task(std::move(f)), delay);
}
// Implementations should provide the behavior explained in the comments above
// for PostTask[WithDelay](). Client code may also call these directly when
// passing an existing Task object.
virtual void PostPackagedTask(Task task) = 0;
virtual void PostPackagedTaskWithDelay(Task task, Clock::duration delay) = 0;
// Return true if the calling thread is the thread that task runner is using
// to run tasks, false otherwise.
virtual bool IsRunningOnTaskRunner() = 0;
};
} // namespace openscreen
#endif // PLATFORM_API_TASK_RUNNER_H_
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