How Can I Implement Semaphores in C 0x Without Using Boost?

Synchronization in C 0x Without Semaphores

C 0x introduces atomic variables and conditions, but lacks explicit semaphore support. This has raised concerns about how to effectively synchronize threads without using Boost's semaphore implementation.

One method involves utilizing a combination of mutexes and condition variables to create a custom-built semaphore. Consider the following example:

#include <mutex>
#include <condition_variable>

class semaphore {
    std::mutex mutex_;
    std::condition_variable condition_;
    unsigned long count_ = 0; // Initialized as locked.

public:
    void release() {
        std::lock_guard<decltype(mutex_)> lock(mutex_);
        ++count_;
        condition_.notify_one();
    }

    void acquire() {
        std::unique_lock<decltype(mutex_)> lock(mutex_);
        while (!count_) // Handle spurious wake-ups.
            condition_.wait(lock);
        --count_;
    }

    bool try_acquire() {
        std::lock_guard<decltype(mutex_)> lock(mutex_);
        if (count_) {
            --count_;
            return true;
        }
        return false;
    }
};

This implementation utilizes a mutex (mutex_) to guard access to the internal data and employs a condition variable (condition_) to signal waiting threads when a semaphore is released. The count_ member variable is initialized to zero, indicating an initially locked state.

To release a semaphore (i.e., make it available for acquisition), the release() method increments the count and notifies any waiting threads. To acquire a semaphore, the acquire() method waits until the count is non-zero. The try_acquire() method attempts to acquire the semaphore non-blockingly, returning true if successful or false otherwise.

This approach provides a simple and efficient way to implement semaphores in C 0x without using Boost. It is similar in functionality to POSIX semaphores, allowing threads to synchronize their execution and communicate events effectively.

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