ThreadPool

Provides low-overhead concurrent scheduling in C++11 through thread pools and work stealing. The thread pool approach allows fine-grained parallelism by minimizing the overhead involved in scheduling a task. The work stealing approach allows efficient balancing of scheduled tasks across available threads.

Why use this library?

• It fulfills common scheduling needs:
  • Performs multiple tasks concurrently.
  • Tasks can be scheduled for an arbitrary later time-point. This provides an efficient replacement for timed waits.
  • A task can spawn subtasks, with a hint that the pool ought to complete them as soon as possible.
• It fulfills some uncommon scheduling needs:
  • The pool can be paused, and later resumed.
• It is designed for efficiency and scalability:
  • Load balancing ensures that as long as there is work to do, it is being done by as many threads as possible.
  • Lock-free data structures use weak atomic orderings; only when those cores that require new tasks are synchronized.
  • No busy-waiting. Idle threads use condition variables to wait without using the CPU.
• It is explicitly documented:
  • Full generated documentation via Doxygen.
  • Memory synchronization between task scheduling and execution is explicitly stated in terms of C++11's memory model.
  • Provides usage recommendations for maximizing performance.

Getting Started

This library consists of a single header and source file. One may compile the source file either as part of one's own project, or as a static library.

Prerequisites

You will require a C++11 compiler. If you are using MinGW-w64, you may require MinGW STD Threads to supply std::thread and similar.

Installing

Either compile threadpool.cpp as part of your project, or compile it as a static library.

Using the library

The library is designed to enable a simple use pattern:

1. Create a ThreadPool object.
2. Give tasks to the pool by calling the pool's schedule(), schedule_subtask(), or schedule_after() methods.
3. Wait for tasks to complete.

Full documentation for this library may be generated using Doxygen.

A simple example of how to the library follows:

#include "threadpool.hpp"

//  Create a new thread pool, letting the implementation determine the number of worker threads to use.
ThreadPool pool;

//  Put a task into the pool. Because this isn't called from within a worker thread, it takes the scheduler's slow path.
pool.schedule([](void)
{
//  Put a task into the pool. This is called from within a worker thread, so it takes the scheduler's fast path.
  pool.schedule([](void) {
    do_something();
  });
 
//  Put a task into the pool, treated as if it were part of the currently running task. This is called from within a worker thread, so it takes the scheduler's fast path.
  pool.schedule_subtask([](void) {
    do_something();
  });

//  Put a task into the pool, to be executed 2 seconds after it is scheduled.
  using namespace std::chrono;
  pool.schedule_after(seconds(2),
  [](void) {
    do_something();
  });
});

//  When the thread pool is destroyed, remaining unexecuted tasks are forgotten.

Authors

• Nathaniel J. McClatchey, PhD - Initial work

License

To encourage people to use this library freely and without concern, this project is licensed under the MIT License.