How to solve common deadlock problems in C++ multi-threaded programming?

How to solve common deadlock problems in C++ multi-threaded programming? Techniques to avoid deadlock: Lock order: Always acquire locks in the same order. Deadlock detection: Use algorithms to detect and resolve deadlocks. Timeout: Set a timeout value for the lock to prevent threads from waiting indefinitely. Priority inversion: Assign different priorities to reduce the possibility of deadlock.

How to solve common deadlock problems in C++ multi-threaded programming

Deadlock overview

Deadlock is a programming error. Where two or more threads are blocked indefinitely, waiting for each other to release the lock. This is usually caused by cyclically dependent locks, where one thread holds lock A and waits for lock B, while another thread holds lock B and waits for lock A.

Techniques to avoid deadlock

The following are common techniques to avoid deadlock:

• Lock order:Always in the same order Get the lock. This helps prevent circular dependencies.
• Deadlock detection: Use the deadlock detection algorithm to detect and resolve deadlocks.
• Timeout: Set a timeout value for the lock to prevent threads from waiting indefinitely.
• Priority inversion: Assign different priorities to threads to reduce the possibility of deadlock.

Practical Case

Let us take the following code example, where two threads try to access a shared resource:

class Resource {
public:
    void increment() {
        std::lock_guard<std::mutex> lock(m_mutex);
        ++m_value;
    }
    int m_value = 0;
    std::mutex m_mutex;
};

int main() {
    Resource resource;
    std::thread thread1([&resource] { resource.increment(); });
    std::thread thread2([&resource] { resource.increment(); });
    thread1.join();
    thread2.join();
}

In this example, thread 1 and 2 Try to acquire the same lock (resource.m_mutex) to update the m_value variable. If thread 1 acquires the lock first, thread 2 will be blocked, and vice versa. This can lead to circular dependencies and deadlocks.

Solution

To fix this problem, we can use locking order. For example, we can let all threads acquire the resource.m_mutex lock first, and then the m_value lock:

class Resource {
public:
    void increment() {
        std::lock(m_mutex, m_value_mutex);
        ++m_value;
        std::unlock(m_value_mutex, m_mutex);
    }
    int m_value = 0;
    std::mutex m_mutex;
    std::mutex m_value_mutex;
};

int main() {
    Resource resource;
    std::thread thread1([&resource] { resource.increment(); });
    std::thread thread2([&resource] { resource.increment(); });
    thread1.join();
    thread2.join();
}

In this way, both threads will acquire the locks in the same order , thereby avoiding deadlock.

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