| //==-- llvm/Support/ThreadPool.cpp - A ThreadPool implementation -*- C++ -*-==// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements a crude C++11 based thread pool. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Support/ThreadPool.h" |
| |
| #include "llvm/Config/llvm-config.h" |
| #include "llvm/Support/Threading.h" |
| #include "llvm/Support/raw_ostream.h" |
| |
| using namespace llvm; |
| |
| #if LLVM_ENABLE_THREADS |
| |
| ThreadPool::ThreadPool(ThreadPoolStrategy S) |
| : ThreadCount(S.compute_thread_count()) { |
| // 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([S, ThreadID, this] { |
| S.apply_thread_strategy(ThreadID); |
| while (true) { |
| std::function<void()> 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; |
| Task = std::move(Tasks.front()); |
| Tasks.pop(); |
| } |
| // Run the task we just grabbed |
| Task(); |
| |
| bool Notify; |
| { |
| // Adjust `ActiveThreads`, in case someone waits on ThreadPool::wait() |
| std::lock_guard<std::mutex> LockGuard(QueueLock); |
| --ActiveThreads; |
| Notify = workCompletedUnlocked(); |
| } |
| // Notify task completion if this is the last active thread, in case |
| // someone waits on ThreadPool::wait(). |
| if (Notify) |
| CompletionCondition.notify_all(); |
| } |
| }); |
| } |
| } |
| |
| void ThreadPool::wait() { |
| // Wait for all threads to complete and the queue to be empty |
| std::unique_lock<std::mutex> LockGuard(QueueLock); |
| CompletionCondition.wait(LockGuard, [&] { return workCompletedUnlocked(); }); |
| } |
| |
| bool ThreadPool::isWorkerThread() const { |
| llvm::thread::id CurrentThreadId = llvm::this_thread::get_id(); |
| for (const llvm::thread &Thread : Threads) |
| if (CurrentThreadId == Thread.get_id()) |
| return true; |
| return false; |
| } |
| |
| // 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 |
| |
| // No threads are launched, issue a warning if ThreadCount is not 0 |
| ThreadPool::ThreadPool(ThreadPoolStrategy S) |
| : ThreadCount(S.compute_thread_count()) { |
| if (ThreadCount != 1) { |
| 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(); |
| } |
| } |
| |
| ThreadPool::~ThreadPool() { wait(); } |
| |
| #endif |