How to debug multi-threaded C++ programs?

Debug multi-threaded C++ programs by using the GDB or LLDB debugger, checking lock order to prevent deadlocks, using synchronization mechanisms to protect shared data, using memory debuggers to detect leaks, and using mutexes and thread-local storage to synchronize access. For example, in the sample code, a mutex is used to synchronize access to cout to prevent output from being out of order.

How to debug multi-threaded C++ programs

Debugging multi-threaded applications can be a challenging task because they Concurrency is increased, and errors are difficult to predict and reproduce. Here are some tips and tools to help you troubleshoot multithreaded C++ programs.

Using the debugger

• GDB: Use the -g compile option to enable debugging information, and then use GDB to debug processor for single-stepping and inspecting variables.
• LLDB: Enable thread hygiene checks using the -Xclang -fsanitize=thread compile option and then debug with the LLDB debugger to detect thread-related errors.

Thread safety issues

• Deadlock: Determine the order of locks causing the deadlock and use an unlocking mechanism or Deadlock detection to resolve it.
• Race conditions: Identify shared data and protect it using synchronization mechanisms such as mutexes or spin locks.
• Data corruption: Ensure that data access between threads is synchronized and use atomic operations or thread-local storage to prevent race conditions.
• Memory leaks: Use a memory debugger (such as Valgrind or AddressSanitizer) to detect memory leaks and release resources that are no longer needed.

Practical case

Sample code:

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

std::mutex mtx;

void thread_function() {
    // 获得锁
    std::lock_guard<std::mutex> lock(mtx);
    std::cout << "Hello from thread" << std::endl;
    // 释放锁
}

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

Question: above In the example, the cout output may be garbled because the output from the two threads is being interleaved.

Solution: Use mutex to synchronize access to shared resources cout:

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

std::mutex mtx;

void thread_function() {
    // 获得锁
    std::lock_guard<std::mutex> lock(mtx);
    std::cout << "Hello from thread" << std::endl;
    // 释放锁
}

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

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