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/*
* Copyright 2016 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//
// Threads helpers.
//
#ifndef wasm_support_threads_h
#define wasm_support_threads_h
#include <atomic>
#include <condition_variable>
#include <functional>
#include <memory>
#include <mutex>
#include <thread>
#include <vector>
namespace wasm {
// The work state of a helper thread - is there more to do,
// or are we finished for now.
enum class ThreadWorkState {
More,
Finished
};
//
// A helper thread.
//
// You can only create and destroy these on the main thread.
//
class Thread {
std::unique_ptr<std::thread> thread;
std::mutex mutex;
std::condition_variable condition;
bool done = false;
std::function<ThreadWorkState ()> doWork = nullptr;
public:
Thread();
~Thread();
// Start to do work, calling doWork() until
// it returns false.
void work(std::function<ThreadWorkState ()> doWork);
private:
static void mainLoop(void *self);
};
//
// A pool of helper threads.
//
// There is only one, to avoid recursive pools using too many cores.
//
class ThreadPool {
std::vector<std::unique_ptr<Thread>> threads;
bool running = false;
std::mutex mutex;
std::condition_variable condition;
std::atomic<size_t> ready;
private:
void initialize(size_t num);
public:
// Get the number of cores we can use.
static size_t getNumCores();
// Get the singleton threadpool.
static ThreadPool* get();
// Execute a bunch of tasks by the pool. This calls
// getTask() (in a thread-safe manner) to get tasks, and
// sends them to workers to be executed. This method
// blocks until all tasks are complete.
void work(std::vector<std::function<ThreadWorkState ()>>& doWorkers);
size_t size();
static bool isRunning();
// Called by helper threads when they are free and ready.
void notifyThreadIsReady();
private:
void resetThreadsAreReady();
bool areThreadsReady();
};
// Verify a code segment is only entered once. Usage:
// static OnlyOnce onlyOnce;
// onlyOnce.verify();
class OnlyOnce {
std::atomic<int> created;
public:
OnlyOnce() {
created.store(0);
}
void verify() {
auto before = created.fetch_add(1);
assert(before == 0);
}
};
} // namespace wasm
#endif // wasm_support_threads_h
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