[llvm] r255444 - Add a C++11 ThreadPool implementation in LLVM
Vedant Kumar via llvm-commits
llvm-commits at lists.llvm.org
Tue Dec 15 10:48:45 PST 2015
Thanks Mehdi!
> On Dec 12, 2015, at 2:55 PM, Mehdi AMINI via llvm-commits <llvm-commits at lists.llvm.org> wrote:
>
> Author: mehdi_amini
> Date: Sat Dec 12 16:55:25 2015
> New Revision: 255444
>
> URL: http://llvm.org/viewvc/llvm-project?rev=255444&view=rev
> Log:
> Add a C++11 ThreadPool implementation in LLVM
>
> This is a very simple implementation of a thread pool using C++11
> thread. It accepts any std::function<void()> for asynchronous
> execution. Individual task can be synchronize using the returned
> future, or the client can block on the full queue completion.
>
> In case LLVM is configured with Threading disabled, it falls back
> to sequential execution using std::async with launch:deferred.
>
> This is intended to support parallelism for ThinLTO processing in
> linker plugin, but is generic enough for any other uses.
>
> Differential Revision: http://reviews.llvm.org/D15464
>
> From: Mehdi Amini <mehdi.amini at apple.com>
>
> Added:
> llvm/trunk/include/llvm/Support/ThreadPool.h
> llvm/trunk/lib/Support/ThreadPool.cpp
> llvm/trunk/unittests/Support/ThreadPool.cpp
> Modified:
> llvm/trunk/include/llvm/Support/thread.h
> llvm/trunk/lib/Support/CMakeLists.txt
> llvm/trunk/unittests/Support/CMakeLists.txt
>
> Added: llvm/trunk/include/llvm/Support/ThreadPool.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/ThreadPool.h?rev=255444&view=auto
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/ThreadPool.h (added)
> +++ llvm/trunk/include/llvm/Support/ThreadPool.h Sat Dec 12 16:55:25 2015
> @@ -0,0 +1,95 @@
> +//===-- llvm/Support/ThreadPool.h - 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 defines a crude C++11 based thread pool.
> +//
> +//===----------------------------------------------------------------------===//
> +
> +#ifndef LLVM_SUPPORT_THREAD_POOL_H
> +#define LLVM_SUPPORT_THREAD_POOL_H
> +
> +#include "llvm/Support/thread.h"
> +
> +#include <condition_variable>
> +#include <functional>
> +#include <future>
> +#include <memory>
> +#include <mutex>
> +#include <queue>
> +#include <utility>
> +
> +namespace llvm {
> +
> +/// A ThreadPool for asynchronous parallel execution on a defined number of
> +/// threads.
> +///
> +/// The pool keeps a vector of threads alive, waiting on a condition variable
> +/// for some work to become available.
> +class ThreadPool {
> +public:
> + using TaskTy = std::function<void()>;
> +
> + /// Construct a pool with the number of core available on the system (or
> + /// whatever the value returned by std::thread::hardware_concurrency() is).
> + ThreadPool();
> +
> + /// Construct a pool of \p ThreadCount threads
> + ThreadPool(unsigned ThreadCount);
> +
> + /// Blocking destructor: the pool will wait for all the threads to complete.
> + ~ThreadPool();
> +
> + /// Asynchronous submission of a task to the pool. The returned future can be
> + /// used to wait for the task to finish and is *non-blocking* on destruction.
> + template <typename Function, typename... Args>
> + inline std::shared_future<void> async(Function &&F, Args &&... ArgList) {
> + auto Task =
> + std::bind(std::forward<Function>(F), std::forward<Args...>(ArgList...));
> + return asyncImpl(Task);
> + }
> +
> + /// Asynchronous submission of a task to the pool. The returned future can be
> + /// used to wait for the task to finish and is *non-blocking* on destruction.
> + template <typename Function>
> + inline std::shared_future<void> async(Function &&F) {
> + return asyncImpl(F);
> + }
> +
> + /// Blocking wait for all the threads to complete and the queue to be empty.
> + /// It is an error to try to add new tasks while blocking on this call.
> + void wait();
> +
> +private:
> + /// Asynchronous submission of a task to the pool. The returned future can be
> + /// used to wait for the task to finish and is *non-blocking* on destruction.
> + std::shared_future<void> asyncImpl(TaskTy f);
> +
> + /// Threads in flight
> + std::vector<llvm::thread> Threads;
> +
> + /// Tasks waiting for execution in the pool.
> + std::queue<std::packaged_task<void()>> Tasks;
> +
> + /// Locking and signaling for accessing the Tasks queue.
> + std::mutex QueueLock;
> + std::condition_variable QueueCondition;
> +
> + /// Locking and signaling for job completion
> + std::mutex CompletionLock;
> + std::condition_variable CompletionCondition;
> +
> + /// Keep track of the number of thread actually busy
> + std::atomic<unsigned> ActiveThreads;
> +
> + /// Signal for the destruction of the pool, asking thread to exit.
> + bool EnableFlag;
> +};
> +}
> +
> +#endif // LLVM_SUPPORT_THREAD_POOL_H
>
> Modified: llvm/trunk/include/llvm/Support/thread.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/thread.h?rev=255444&r1=255443&r2=255444&view=diff
> ==============================================================================
> --- llvm/trunk/include/llvm/Support/thread.h (original)
> +++ llvm/trunk/include/llvm/Support/thread.h Sat Dec 12 16:55:25 2015
> @@ -43,6 +43,8 @@ typedef std::thread thread;
>
> #else // !LLVM_ENABLE_THREADS
>
> +#include <utility>
> +
> namespace llvm {
>
> struct thread {
>
> Modified: llvm/trunk/lib/Support/CMakeLists.txt
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/CMakeLists.txt?rev=255444&r1=255443&r2=255444&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Support/CMakeLists.txt (original)
> +++ llvm/trunk/lib/Support/CMakeLists.txt Sat Dec 12 16:55:25 2015
> @@ -89,6 +89,7 @@ add_llvm_library(LLVMSupport
> StringRef.cpp
> SystemUtils.cpp
> TargetParser.cpp
> + ThreadPool.cpp
> Timer.cpp
> ToolOutputFile.cpp
> Triple.cpp
>
> Added: llvm/trunk/lib/Support/ThreadPool.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/ThreadPool.cpp?rev=255444&view=auto
> ==============================================================================
> --- llvm/trunk/lib/Support/ThreadPool.cpp (added)
> +++ llvm/trunk/lib/Support/ThreadPool.cpp Sat Dec 12 16:55:25 2015
> @@ -0,0 +1,143 @@
> +//==-- 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) {
> + std::packaged_task<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;
> + std::unique_lock<std::mutex> LockGuard(CompletionLock);
> + }
> + Task = std::move(Tasks.front());
> + Tasks.pop();
> + }
> + // Run the task we just grabbed
> + Task();
> +
> + {
> + // 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<void> ThreadPool::asyncImpl(TaskTy Task) {
> + /// Wrap the Task in a packaged_task to return a future object.
> + std::packaged_task<void()> PackagedTask(std::move(Task));
> + std::future<void> 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), EnableFlag(true) {
> + 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<void> 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.
> + std::packaged_task<void()> PackagedTask([Future]() { Future.get(); });
> + Tasks.push(std::move(PackagedTask));
> + return Future;
> +}
> +
> +ThreadPool::~ThreadPool() {
> + EnableFlag = false;
> + wait();
> +}
> +
> +#endif
>
> Modified: llvm/trunk/unittests/Support/CMakeLists.txt
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/CMakeLists.txt?rev=255444&r1=255443&r2=255444&view=diff
> ==============================================================================
> --- llvm/trunk/unittests/Support/CMakeLists.txt (original)
> +++ llvm/trunk/unittests/Support/CMakeLists.txt Sat Dec 12 16:55:25 2015
> @@ -41,6 +41,7 @@ add_llvm_unittest(SupportTests
> SwapByteOrderTest.cpp
> TargetRegistry.cpp
> ThreadLocalTest.cpp
> + ThreadPool.cpp
> TimeValueTest.cpp
> TrailingObjectsTest.cpp
> UnicodeTest.cpp
>
> Added: llvm/trunk/unittests/Support/ThreadPool.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/unittests/Support/ThreadPool.cpp?rev=255444&view=auto
> ==============================================================================
> --- llvm/trunk/unittests/Support/ThreadPool.cpp (added)
> +++ llvm/trunk/unittests/Support/ThreadPool.cpp Sat Dec 12 16:55:25 2015
> @@ -0,0 +1,91 @@
> +//========- unittests/Support/ThreadPools.cpp - ThreadPools.h tests --========//
> +//
> +// The LLVM Compiler Infrastructure
> +//
> +// This file is distributed under the University of Illinois Open Source
> +// License. See LICENSE.TXT for details.
> +//
> +//===----------------------------------------------------------------------===//
> +
> +#include "llvm/Support/ThreadPool.h"
> +
> +#include "llvm/ADT/STLExtras.h"
> +
> +#include "gtest/gtest.h"
> +
> +using namespace llvm;
> +using namespace std::chrono;
> +
> +/// Try best to make this thread not progress faster than the main thread
> +static void yield() {
> +#ifdef LLVM_ENABLE_THREADS
> + std::this_thread::yield();
> +#endif
> + std::this_thread::sleep_for(milliseconds(200));
> +#ifdef LLVM_ENABLE_THREADS
> + std::this_thread::yield();
> +#endif
> +}
> +
> +TEST(ThreadPoolTest, AsyncBarrier) {
> + // test that async & barrier work together properly.
> +
> + std::atomic_int checked_in{0};
> +
> + ThreadPool Pool;
> + for (size_t i = 0; i < 5; ++i) {
> + Pool.async([&checked_in, i] {
> + yield();
> + ++checked_in;
> + });
> + }
> + ASSERT_EQ(0, checked_in);
> + Pool.wait();
> + ASSERT_EQ(5, checked_in);
> +}
> +
> +TEST(ThreadPoolTest, Async) {
> + ThreadPool Pool;
> + std::atomic_int i{0};
> + // sleep here just to ensure that the not-equal is correct.
> + Pool.async([&i] {
> + yield();
> + ++i;
> + });
> + Pool.async([&i] { ++i; });
> + ASSERT_NE(2, i.load());
> + Pool.wait();
> + ASSERT_EQ(2, i.load());
> +}
> +
> +TEST(ThreadPoolTest, GetFuture) {
> + ThreadPool Pool;
> + std::atomic_int i{0};
> + // sleep here just to ensure that the not-equal is correct.
> + Pool.async([&i] {
> + yield();
> + ++i;
> + });
> + // Force the future using get()
> + Pool.async([&i] { ++i; }).get();
> + ASSERT_NE(2, i.load());
> + Pool.wait();
> + ASSERT_EQ(2, i.load());
> +}
> +
> +TEST(ThreadPoolTest, PoolDestruction) {
> + // Test that we are waiting on destruction
> + std::atomic_int checked_in{0};
> +
> + {
> + ThreadPool Pool;
> + for (size_t i = 0; i < 5; ++i) {
> + Pool.async([&checked_in, i] {
> + yield();
> + ++checked_in;
> + });
> + }
> + ASSERT_EQ(0, checked_in);
> + }
> + ASSERT_EQ(5, checked_in);
> +}
>
>
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