What are some examples of deadlock scenarios in C++?

What are some examples of deadlock scenarios in C++?

Deadlock occurs when two or more threads are blocked forever, each waiting on the other. A classic example is when two threads hold locks on two resources and each thread tries to acquire the lock held by the other.

Can you give a specific code example of this?

Sure! Here's a simple example:

#include <iostream>
#include <thread>
#include <mutex>

std::mutex mutex1;
std::mutex mutex2;

void thread1() {
    std::lock_guard<std::mutex> lock1(mutex1);
    std::this_thread::sleep_for(std::chrono::milliseconds(100));
    std::lock_guard<std::mutex> lock2(mutex2);
}

void thread2() {
    std::lock_guard<std::mutex> lock2(mutex2);
    std::this_thread::sleep_for(std::chrono::milliseconds(100));
    std::lock_guard<std::mutex> lock1(mutex1);
}

int main() {
    std::thread t1(thread1);
    std::thread t2(thread2);
    t1.join();
    t2.join();
    return 0;
}

In this example, thread1 locks mutex1 and then tries to lock mutex2, while thread2 does the opposite, leading to a deadlock.

How can I avoid deadlocks in my code?

To avoid deadlocks, you can use several strategies:

1. Lock ordering: Always acquire locks in a consistent order.
2. Timeouts: Use timeouts when trying to acquire locks.
3. Try-lock: Use try-lock mechanisms to avoid blocking indefinitely.