1 //==-- llvm/Support/ThreadPool.cpp - A ThreadPool implementation -*- C++ -*-==// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file implements a crude C++11 based thread pool. 10 // 11 //===----------------------------------------------------------------------===// 12 13 #include "llvm/Support/ThreadPool.h" 14 15 #include "llvm/Config/llvm-config.h" 16 #include "llvm/Support/Threading.h" 17 #include "llvm/Support/raw_ostream.h" 18 19 using namespace llvm; 20 21 #if LLVM_ENABLE_THREADS 22 23 ThreadPool::ThreadPool(ThreadPoolStrategy S) 24 : ThreadCount(S.compute_thread_count()) { 25 // Create ThreadCount threads that will loop forever, wait on QueueCondition 26 // for tasks to be queued or the Pool to be destroyed. 27 Threads.reserve(ThreadCount); 28 for (unsigned ThreadID = 0; ThreadID < ThreadCount; ++ThreadID) { 29 Threads.emplace_back([S, ThreadID, this] { 30 S.apply_thread_strategy(ThreadID); 31 while (true) { 32 std::function<void()> Task; 33 { 34 std::unique_lock<std::mutex> LockGuard(QueueLock); 35 // Wait for tasks to be pushed in the queue 36 QueueCondition.wait(LockGuard, 37 [&] { return !EnableFlag || !Tasks.empty(); }); 38 // Exit condition 39 if (!EnableFlag && Tasks.empty()) 40 return; 41 // Yeah, we have a task, grab it and release the lock on the queue 42 43 // We first need to signal that we are active before popping the queue 44 // in order for wait() to properly detect that even if the queue is 45 // empty, there is still a task in flight. 46 ++ActiveThreads; 47 Task = std::move(Tasks.front()); 48 Tasks.pop(); 49 } 50 // Run the task we just grabbed 51 Task(); 52 53 bool Notify; 54 { 55 // Adjust `ActiveThreads`, in case someone waits on ThreadPool::wait() 56 std::lock_guard<std::mutex> LockGuard(QueueLock); 57 --ActiveThreads; 58 Notify = workCompletedUnlocked(); 59 } 60 // Notify task completion if this is the last active thread, in case 61 // someone waits on ThreadPool::wait(). 62 if (Notify) 63 CompletionCondition.notify_all(); 64 } 65 }); 66 } 67 } 68 69 void ThreadPool::wait() { 70 // Wait for all threads to complete and the queue to be empty 71 std::unique_lock<std::mutex> LockGuard(QueueLock); 72 CompletionCondition.wait(LockGuard, [&] { return workCompletedUnlocked(); }); 73 } 74 75 bool ThreadPool::isWorkerThread() const { 76 llvm::thread::id CurrentThreadId = llvm::this_thread::get_id(); 77 for (const llvm::thread &Thread : Threads) 78 if (CurrentThreadId == Thread.get_id()) 79 return true; 80 return false; 81 } 82 83 // The destructor joins all threads, waiting for completion. 84 ThreadPool::~ThreadPool() { 85 { 86 std::unique_lock<std::mutex> LockGuard(QueueLock); 87 EnableFlag = false; 88 } 89 QueueCondition.notify_all(); 90 for (auto &Worker : Threads) 91 Worker.join(); 92 } 93 94 #else // LLVM_ENABLE_THREADS Disabled 95 96 // No threads are launched, issue a warning if ThreadCount is not 0 97 ThreadPool::ThreadPool(ThreadPoolStrategy S) 98 : ThreadCount(S.compute_thread_count()) { 99 if (ThreadCount != 1) { 100 errs() << "Warning: request a ThreadPool with " << ThreadCount 101 << " threads, but LLVM_ENABLE_THREADS has been turned off\n"; 102 } 103 } 104 105 void ThreadPool::wait() { 106 // Sequential implementation running the tasks 107 while (!Tasks.empty()) { 108 auto Task = std::move(Tasks.front()); 109 Tasks.pop(); 110 Task(); 111 } 112 } 113 114 ThreadPool::~ThreadPool() { wait(); } 115 116 #endif 117