How to deal with thread synchronization issues in C++ development

How to deal with thread synchronization issues in C development

In the C development process, multi-threaded applications are becoming more and more common. However, multi-threaded programming often faces various thread synchronization problems, such as race conditions, deadlocks, etc. Correctly handling thread synchronization issues is critical to ensuring program correctness and performance. This article will introduce several common thread synchronization problems and corresponding solutions.

1. Race conditions
Race conditions refer to errors caused by the unpredictable execution order when multiple threads access shared resources. For example, writing to the same variable simultaneously in multiple threads can lead to data errors. To avoid race conditions, a mutex can be used to ensure that only one thread can access a shared resource at a time. Mutex locks can achieve mutually exclusive access to resources through the lock() and unlock() methods.

Sample code:

#include <mutex>

std::mutex mutex;

// 线程A
void threadA() {
    mutex.lock();
    // 访问共享资源
    mutex.unlock();
}

// 线程B
void threadB() {
    mutex.lock();
    // 访问共享资源
    mutex.unlock();
}

2. Deadlock
Deadlock refers to a cyclic waiting state caused by multiple threads waiting for each other to release resources. For example, thread A holds lock A but wants to acquire lock B, and thread B holds lock B but wants to acquire lock A. Since both parties do not release resources from each other, a deadlock occurs. To avoid deadlock, locking order can be used to avoid cyclic waiting.

Sample code:

std::mutex mutexA;
std::mutex mutexB;

// 线程A
void threadA() {
    mutexA.lock();
    // 访问资源A
    mutexB.lock();
    // 访问资源B
    mutexB.unlock();
    mutexA.unlock();
}

// 线程B
void threadB() {
    mutexA.lock(); // 交换了锁A和锁B的加锁顺序
    // 访问资源A
    mutexB.lock();
    // 访问资源B
    mutexB.unlock();
    mutexA.unlock();
}

3. Condition variable
Condition variable is a thread synchronization mechanism that allows a thread to wait until a specific condition is met. Condition variables are often used with mutex locks to avoid race conditions. The thread can be put into the waiting state through the wait() method, and the waiting thread can be awakened through the notify() or notify_all() method.

Sample code:

#include <condition_variable>
#include <mutex>

std::mutex mutex;
std::condition_variable condVar;
bool isReady = false;

// 线程A
void threadA() {
    std::unique_lock<std::mutex> lock(mutex);
    while (!isReady) {
        condVar.wait(lock);
    }
    // 执行任务
}

// 线程B
void threadB() {
    std::unique_lock<std::mutex> lock(mutex);
    // 执行任务
    isReady = true;
    condVar.notify_one();
}

4. Semaphore
Semaphore is a mechanism for thread synchronization that avoids race conditions by controlling the number of threads that access shared resources at the same time. A semaphore can be understood as a counter, and its initial value represents the number of threads that can access shared resources at the same time. When a thread needs to access a shared resource, it will try to perform a P operation (decrease 1) on the semaphore. If the value of the semaphore becomes a negative number, the thread will enter a waiting state; when the thread releases the shared resource, it will try to perform a P operation on the semaphore (decrease 1). Perform V operation (add 1) to the amount to wake up the waiting thread.

Sample code:

#include <semaphore.h>

sem_t semaphore;

// 线程A
void threadA() {
    sem_wait(&semaphore);
    // 访问共享资源
    sem_post(&semaphore);
}

// 线程B
void threadB() {
    sem_wait(&semaphore);
    // 访问共享资源
    sem_post(&semaphore);
}

After the above introduction, we can see that by using thread synchronization mechanisms such as mutex locks, locking sequences, condition variables and semaphores, we can effectively Handle thread synchronization issues in C development. Correctly handling thread synchronization issues can not only ensure the correctness of the program, but also improve the performance and concurrency of the program. In actual development, it is necessary to choose an appropriate thread synchronization mechanism to solve the problem according to the specific situation to ensure the stability and reliability of the program.

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