Creating a thread pool in C requires manual implementation. 1. The thread pool includes thread arrays, task queues, synchronization mechanisms and control switches; 2. The constructor starts the thread and enters a waiting state, notifies the thread to exit and wait for completion during destruction; 3. Add tasks to the queue through template functions and wakes up the thread to execute; 4. When using it, avoid problems such as uncaught exceptions, long-term blocking, unprocessed dependencies and dangling references.
Creating a thread pool in C is mainly achieved by manually managing a set of threads and providing task queues and scheduling mechanisms. The C 11 standard provides basic components such as <thread></thread> , <mutex></mutex> , <condition_variable></condition_variable> and <functional></functional> , which can be used to build a simple thread pool.
1. Define the basic structure of thread pool
A thread pool usually contains the following core components:
- Thread array : used to store multiple worker threads.
- Task queue : Stores tasks to be executed (usually function objects).
- Synchronization mechanism : includes mutex locks and condition variables to ensure multi-threaded safe access to queues.
- Control switch : For example, the flag of whether to stop the thread pool.
The basic class definition is as follows:
class ThreadPool {
public:
ThreadPool(size_t numThreads);
~ThreadPool();
template<class F>
void enqueue(F&& task);
private:
std::vector<std::thread> workers;
std::queue<std::function<void()>> tasks;
std::mutex queue_mutex;
std::condition_variable condition;
bool stop = false;
};2. Implement construction and destructuring logic
The specified number of threads is started in the constructor, and each thread enters a waiting state until a task arrives.
ThreadPool::ThreadPool(size_t numThreads) {
for (size_t i = 0; i < numThreads; i) {
workers.emplace_back([this] {
while (true) {
std::function<void()> task;
{
std::unique_lock<std::mutex> lock(this->queue_mutex);
this->condition.wait(lock, [this] {
return this->stop || !this->tasks.empty();
});
if (this->stop && this->tasks.empty()) {
return;
}
task = std::move(this->tasks.front());
this->tasks.pop();
}
task();
}
});
}
}In the destructor, all threads are notified to exit and wait for them to complete:
ThreadPool::~ThreadPool() {
{
std::unique_lock<std::mutex> lock(queue_mutex);
stop = true;
}
condition.notify_all();
for (std::thread &worker : workers) {
if (worker.joinable()) {
worker.join();
}
}
}3. Add tasks to thread pool
Use the template function to wrap any callable object into std::function<void()> and add it to the queue:
template<class F>
void ThreadPool::enqueue(F&& task) {
{
std::unique_lock<std::mutex> lock(queue_mutex);
tasks.emplace(std::forward<F>(task));
}
condition.notify_one();
} In this way, you can submit the task through pool.enqueue([]{ ... }); ;.
4. Examples of use and precautions
You can use this thread pool like this:
ThreadPool pool(4);
for (int i = 0; i < 10; i) {
pool.enqueue([i]{
std::cout << "Task " << i << " is running on thread "
<< std::this_thread::get_id() << std::endl;
});
}A few points to note:
- Avoid throwing uncaught exceptions in the task, otherwise it will cause the entire program to crash.
- Do not block in tasks for a long time to avoid affecting the execution of other tasks.
- If there are dependencies between tasks, additional synchronization issues need to be handled.
- Consider using smart pointers or binders to avoid dangling references.
Basically that's it. Although the standard library does not have a built-in thread pool, a lightweight version can be easily implemented with the help of C 11's concurrency tools.
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