-//==-- llvm/Support/ThreadPool.cpp - A ThreadPool implementation -*- C++ -*-==//
-//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This file implements a crude C++11 based thread pool.
-//
-//===----------------------------------------------------------------------===//
-
-#include "llvm/Support/ThreadPool.h"
-
-#include "llvm/Config/llvm-config.h"
-#include "llvm/Support/raw_ostream.h"
-
-using namespace llvm;
-
-#if LLVM_ENABLE_THREADS
-
-// Default to std::thread::hardware_concurrency
-ThreadPool::ThreadPool() : ThreadPool(std::thread::hardware_concurrency()) {}
-
-ThreadPool::ThreadPool(unsigned ThreadCount)
- : ActiveThreads(0), EnableFlag(true) {
- // Create ThreadCount threads that will loop forever, wait on QueueCondition
- // for tasks to be queued or the Pool to be destroyed.
- Threads.reserve(ThreadCount);
- for (unsigned ThreadID = 0; ThreadID < ThreadCount; ++ThreadID) {
- Threads.emplace_back([&] {
- while (true) {
- PackagedTaskTy Task;
- {
- std::unique_lock<std::mutex> LockGuard(QueueLock);
- // Wait for tasks to be pushed in the queue
- QueueCondition.wait(LockGuard,
- [&] { return !EnableFlag || !Tasks.empty(); });
- // Exit condition
- if (!EnableFlag && Tasks.empty())
- return;
- // Yeah, we have a task, grab it and release the lock on the queue
-
- // We first need to signal that we are active before popping the queue
- // in order for wait() to properly detect that even if the queue is
- // empty, there is still a task in flight.
- {
- ++ActiveThreads;
- std::unique_lock<std::mutex> LockGuard(CompletionLock);
- }
- Task = std::move(Tasks.front());
- Tasks.pop();
- }
- // Run the task we just grabbed
-#ifndef _MSC_VER
- Task();
-#else
- Task(/* unused */ false);
-#endif
-
- {
- // Adjust `ActiveThreads`, in case someone waits on ThreadPool::wait()
- std::unique_lock<std::mutex> LockGuard(CompletionLock);
- --ActiveThreads;
- }
-
- // Notify task completion, in case someone waits on ThreadPool::wait()
- CompletionCondition.notify_all();
- }
- });
- }
-}
-
-void ThreadPool::wait() {
- // Wait for all threads to complete and the queue to be empty
- std::unique_lock<std::mutex> LockGuard(CompletionLock);
- CompletionCondition.wait(LockGuard,
- [&] { return Tasks.empty() && !ActiveThreads; });
-}
-
-std::shared_future<ThreadPool::VoidTy> ThreadPool::asyncImpl(TaskTy Task) {
- /// Wrap the Task in a packaged_task to return a future object.
- PackagedTaskTy PackagedTask(std::move(Task));
- auto Future = PackagedTask.get_future();
- {
- // Lock the queue and push the new task
- std::unique_lock<std::mutex> LockGuard(QueueLock);
-
- // Don't allow enqueueing after disabling the pool
- assert(EnableFlag && "Queuing a thread during ThreadPool destruction");
-
- Tasks.push(std::move(PackagedTask));
- }
- QueueCondition.notify_one();
- return Future.share();
-}
-
-// The destructor joins all threads, waiting for completion.
-ThreadPool::~ThreadPool() {
- {
- std::unique_lock<std::mutex> LockGuard(QueueLock);
- EnableFlag = false;
- }
- QueueCondition.notify_all();
- for (auto &Worker : Threads)
- Worker.join();
-}
-
-#else // LLVM_ENABLE_THREADS Disabled
-
-ThreadPool::ThreadPool() : ThreadPool(0) {}
-
-// No threads are launched, issue a warning if ThreadCount is not 0
-ThreadPool::ThreadPool(unsigned ThreadCount)
- : ActiveThreads(0) {
- if (ThreadCount) {
- errs() << "Warning: request a ThreadPool with " << ThreadCount
- << " threads, but LLVM_ENABLE_THREADS has been turned off\n";
- }
-}
-
-void ThreadPool::wait() {
- // Sequential implementation running the tasks
- while (!Tasks.empty()) {
- auto Task = std::move(Tasks.front());
- Tasks.pop();
- Task();
- }
-}
-
-std::shared_future<ThreadPool::VoidTy> ThreadPool::asyncImpl(TaskTy Task) {
- // Get a Future with launch::deferred execution using std::async
- auto Future = std::async(std::launch::deferred, std::move(Task)).share();
- // Wrap the future so that both ThreadPool::wait() can operate and the
- // returned future can be sync'ed on.
- PackagedTaskTy PackagedTask([Future]() { Future.get(); });
- Tasks.push(std::move(PackagedTask));
- return Future;
-}
-
-ThreadPool::~ThreadPool() {
- wait();
-}
-
-#endif