Deadlock prevention and detection mechanism in C++ multi-threaded programming

Multi-thread deadlock prevention mechanism includes: 1. Lock sequence; 2. Test and set up. Detection mechanisms include: 1. Timeout; 2. Deadlock detector. The article takes an example of a shared bank account and avoids deadlock through lock sequence. The transfer function first requests the lock of the transfer out account and then the transfer in account.

Deadlock prevention and detection mechanism in C++ multi-threaded programming

In a multi-threaded environment, deadlock is a common errors that may cause the program to stop responding. A deadlock occurs when multiple threads wait indefinitely for each other to release their locks, creating a waiting loop.

In order to avoid and detect deadlocks, C++ provides several mechanisms:

Prevention mechanism

• Lock order: Develop a strict request lock order for all shared mutable data to ensure that all threads always request locks in the same order.
• Test and set: Use std::atomic provided by the std::atomic library to test and set variables to check whether the lock has been request and then set it up immediately.

Detection mechanism

• Timeout:Set a timeout for the lock request. If the lock is not obtained after the time, then Throw an exception or take other appropriate action.
• Deadlock Detector: Use third-party libraries such as Boost.Thread to monitor thread activity, detect deadlocks and take necessary actions.

Practical case:

Consider the following shared bank account example:

class BankAccount {
private:
    std::mutex m_;
    int balance_;
public:
    void deposit(int amount) {
        std::lock_guard<std::mutex> lock(m_);
        balance_ += amount;
    }

    bool withdraw(int amount) {
        std::lock_guard<std::mutex> lock(m_);
        if (balance_ >= amount) {
            balance_ -= amount;
            return true;
        }
        return false;
    }
};

The way to avoid deadlock is to use lock order: request first deposit() lock, and then request withdraw() lock.

void transfer(BankAccount& from, BankAccount& to, int amount) {
    std::lock_guard<std::mutex> fromLock(from.m_);
    std::lock_guard<std::mutex> toLock(to.m_);

    if (from.withdraw(amount)) {
        to.deposit(amount);
    }
}

Deadlock can be prevented by requesting locks in the order of transfers.

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