EIC code displayed by LXR master/​include/​llvm/​Support/​ThreadPool.h	Source navigation Diff markup Identifier search General search
	Version: master test Revert   Change

File indexing completed on 2026-05-10 08:44:34

 //===-- llvm/Support/ThreadPool.h - 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 defines a crude C++11 based thread pool.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_THREADPOOL_H
 #define LLVM_SUPPORT_THREADPOOL_H
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/RWMutex.h"
 #include "llvm/Support/Threading.h"
 #include "llvm/Support/thread.h"
 
 #include <future>
 
 #include <condition_variable>
 #include <deque>
 #include <functional>
 #include <memory>
 #include <mutex>
 #include <utility>
 
 namespace llvm {
 
 class ThreadPoolTaskGroup;
 
 /// This defines the abstract base interface for a ThreadPool allowing
 /// asynchronous parallel execution on a defined number of threads.
 ///
 /// It is possible to reuse one thread pool for different groups of tasks
 /// by grouping tasks using ThreadPoolTaskGroup. All tasks are processed using
 /// the same queue, but it is possible to wait only for a specific group of
 /// tasks to finish.
 ///
 /// It is also possible for worker threads to submit new tasks and wait for
 /// them. Note that this may result in a deadlock in cases such as when a task
 /// (directly or indirectly) tries to wait for its own completion, or when all
 /// available threads are used up by tasks waiting for a task that has no thread
 /// left to run on (this includes waiting on the returned future). It should be
 /// generally safe to wait() for a group as long as groups do not form a cycle.
 class ThreadPoolInterface {
   /// The actual method to enqueue a task to be defined by the concrete
   /// implementation.
   virtual void asyncEnqueue(std::function<void()> Task,
                             ThreadPoolTaskGroup *Group) = 0;
 
 public:
   /// Destroying the pool will drain the pending tasks and wait. The current
   /// thread may participate in the execution of the pending tasks.
   virtual ~ThreadPoolInterface();
 
   /// 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.
   /// Calling wait() from a task would deadlock waiting for itself.
   virtual void wait() = 0;
 
   /// Blocking wait for only all the threads in the given group to complete.
   /// It is possible to wait even inside a task, but waiting (directly or
   /// indirectly) on itself will deadlock. If called from a task running on a
   /// worker thread, the call may process pending tasks while waiting in order
   /// not to waste the thread.
   virtual void wait(ThreadPoolTaskGroup &Group) = 0;
 
   /// Returns the maximum number of worker this pool can eventually grow to.
   virtual unsigned getMaxConcurrency() const = 0;
 
   /// 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>
   auto async(Function &&F, Args &&...ArgList) {
     auto Task =
         std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...);
     return async(std::move(Task));
   }
 
   /// Overload, task will be in the given task group.
   template <typename Function, typename... Args>
   auto async(ThreadPoolTaskGroup &Group, Function &&F, Args &&...ArgList) {
     auto Task =
         std::bind(std::forward<Function>(F), std::forward<Args>(ArgList)...);
     return async(Group, std::move(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 Func>
   auto async(Func &&F) -> std::shared_future<decltype(F())> {
     return asyncImpl(std::function<decltype(F())()>(std::forward<Func>(F)),
                      nullptr);
   }
 
   template <typename Func>
   auto async(ThreadPoolTaskGroup &Group, Func &&F)
       -> std::shared_future<decltype(F())> {
     return asyncImpl(std::function<decltype(F())()>(std::forward<Func>(F)),
                      &Group);
   }
 
 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.
   template <typename ResTy>
   std::shared_future<ResTy> asyncImpl(std::function<ResTy()> Task,
                                       ThreadPoolTaskGroup *Group) {
     auto Future = std::async(std::launch::deferred, std::move(Task)).share();
     asyncEnqueue([Future]() { Future.wait(); }, Group);
     return Future;
   }
 };
 
 #if LLVM_ENABLE_THREADS
 /// A ThreadPool implementation using std::threads.
 ///
 /// The pool keeps a vector of threads alive, waiting on a condition variable
 /// for some work to become available.
 class StdThreadPool : public ThreadPoolInterface {
 public:
   /// Construct a pool using the hardware strategy \p S for mapping hardware
   /// execution resources (threads, cores, CPUs)
   /// Defaults to using the maximum execution resources in the system, but
   /// accounting for the affinity mask.
   StdThreadPool(ThreadPoolStrategy S = hardware_concurrency());
 
   /// Blocking destructor: the pool will wait for all the threads to complete.
   ~StdThreadPool() override;
 
   /// 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.
   /// Calling wait() from a task would deadlock waiting for itself.
   void wait() override;
 
   /// Blocking wait for only all the threads in the given group to complete.
   /// It is possible to wait even inside a task, but waiting (directly or
   /// indirectly) on itself will deadlock. If called from a task running on a
   /// worker thread, the call may process pending tasks while waiting in order
   /// not to waste the thread.
   void wait(ThreadPoolTaskGroup &Group) override;
 
   /// Returns the maximum number of worker threads in the pool, not the current
   /// number of threads!
   unsigned getMaxConcurrency() const override { return MaxThreadCount; }
 
   // TODO: Remove, misleading legacy name warning!
   LLVM_DEPRECATED("Use getMaxConcurrency instead", "getMaxConcurrency")
   unsigned getThreadCount() const { return MaxThreadCount; }
 
   /// Returns true if the current thread is a worker thread of this thread pool.
   bool isWorkerThread() const;
 
 private:
   /// Returns true if all tasks in the given group have finished (nullptr means
   /// all tasks regardless of their group). QueueLock must be locked.
   bool workCompletedUnlocked(ThreadPoolTaskGroup *Group) const;
 
   /// 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.
   void asyncEnqueue(std::function<void()> Task,
                     ThreadPoolTaskGroup *Group) override {
     int requestedThreads;
     {
       // 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.emplace_back(std::make_pair(std::move(Task), Group));
       requestedThreads = ActiveThreads + Tasks.size();
     }
     QueueCondition.notify_one();
     grow(requestedThreads);
   }
 
   /// Grow to ensure that we have at least `requested` Threads, but do not go
   /// over MaxThreadCount.
   void grow(int requested);
 
   void processTasks(ThreadPoolTaskGroup *WaitingForGroup);
 
   /// Threads in flight
   std::vector<llvm::thread> Threads;
   /// Lock protecting access to the Threads vector.
   mutable llvm::sys::RWMutex ThreadsLock;
 
   /// Tasks waiting for execution in the pool.
   std::deque<std::pair<std::function<void()>, ThreadPoolTaskGroup *>> Tasks;
 
   /// Locking and signaling for accessing the Tasks queue.
   std::mutex QueueLock;
   std::condition_variable QueueCondition;
 
   /// Signaling for job completion (all tasks or all tasks in a group).
   std::condition_variable CompletionCondition;
 
   /// Keep track of the number of thread actually busy
   unsigned ActiveThreads = 0;
   /// Number of threads active for tasks in the given group (only non-zero).
   DenseMap<ThreadPoolTaskGroup *, unsigned> ActiveGroups;
 
   /// Signal for the destruction of the pool, asking thread to exit.
   bool EnableFlag = true;
 
   const ThreadPoolStrategy Strategy;
 
   /// Maximum number of threads to potentially grow this pool to.
   const unsigned MaxThreadCount;
 };
 #endif // LLVM_ENABLE_THREADS
 
 /// A non-threaded implementation.
 class SingleThreadExecutor : public ThreadPoolInterface {
 public:
   /// Construct a non-threaded pool, ignoring using the hardware strategy.
   SingleThreadExecutor(ThreadPoolStrategy ignored = {});
 
   /// Blocking destructor: the pool will first execute the pending tasks.
   ~SingleThreadExecutor() override;
 
   /// Blocking wait for all the tasks to execute first
   void wait() override;
 
   /// Blocking wait for only all the tasks in the given group to complete.
   void wait(ThreadPoolTaskGroup &Group) override;
 
   /// Returns always 1: there is no concurrency.
   unsigned getMaxConcurrency() const override { return 1; }
 
   // TODO: Remove, misleading legacy name warning!
   LLVM_DEPRECATED("Use getMaxConcurrency instead", "getMaxConcurrency")
   unsigned getThreadCount() const { return 1; }
 
   /// Returns true if the current thread is a worker thread of this thread pool.
   bool isWorkerThread() const;
 
 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.
   void asyncEnqueue(std::function<void()> Task,
                     ThreadPoolTaskGroup *Group) override {
     Tasks.emplace_back(std::make_pair(std::move(Task), Group));
   }
 
   /// Tasks waiting for execution in the pool.
   std::deque<std::pair<std::function<void()>, ThreadPoolTaskGroup *>> Tasks;
 };
 
 #if LLVM_ENABLE_THREADS
 using DefaultThreadPool = StdThreadPool;
 #else
 using DefaultThreadPool = SingleThreadExecutor;
 #endif
 
 /// A group of tasks to be run on a thread pool. Thread pool tasks in different
 /// groups can run on the same threadpool but can be waited for separately.
 /// It is even possible for tasks of one group to submit and wait for tasks
 /// of another group, as long as this does not form a loop.
 class ThreadPoolTaskGroup {
 public:
   /// The ThreadPool argument is the thread pool to forward calls to.
   ThreadPoolTaskGroup(ThreadPoolInterface &Pool) : Pool(Pool) {}
 
   /// Blocking destructor: will wait for all the tasks in the group to complete
   /// by calling ThreadPool::wait().
   ~ThreadPoolTaskGroup() { wait(); }
 
   /// Calls ThreadPool::async() for this group.
   template <typename Function, typename... Args>
   inline auto async(Function &&F, Args &&...ArgList) {
     return Pool.async(*this, std::forward<Function>(F),
                       std::forward<Args>(ArgList)...);
   }
 
   /// Calls ThreadPool::wait() for this group.
   void wait() { Pool.wait(*this); }
 
 private:
   ThreadPoolInterface &Pool;
 };
 
 } // namespace llvm
 
 #endif // LLVM_SUPPORT_THREADPOOL_H

This page was automatically generated by the 2.3.7 LXR engine. The LXR team