How to Effectively Propagate Exceptions Between Threads in C ?

Propagating Exceptions Between Threads

Introduction:

In multithreaded applications, it is crucial to handle exceptions effectively to prevent unexpected application crashes. When working with multiple threads, exceptions that occur on worker threads should be gracefully propagated back to the main thread for handling, ensuring that the application remains stable.

Solution Using Exception Pointers:

C 11 introduced the concept of exception pointers (exception_ptr), which allow exceptions to be transported across thread boundaries. Exception pointers hold a shared pointer reference to the exception object. Here's an example:

<code class="cpp">#include <thread>
#include <exception>

std::exception_ptr exceptionPtr;

void workerThread() {
    try {
        // Perform some task with potential exceptions
    }
    catch(...) {
        exceptionPtr = std::current_exception();
    }
}

int main() {
    std::thread worker(workerThread);
    worker.join();

    if (exceptionPtr) {
        try {
            std::rethrow_exception(exceptionPtr);
        }
        catch (const std::exception& ex) {
            // Handle the exception on the main thread
            std::cerr << "Exception occurred on worker thread: " << ex.what() << "\n";
        }
    }

    return 0;
}</code>

In this solution, the exception pointer is created on the worker thread and assigned a reference to the caught exception. The main thread then checks if an exception pointer exists and rethrows the exception for handling.

Note:

• This approach supports all C exceptions, including standard library exceptions and custom exceptions.
• It can be used effectively with multiple worker threads by maintaining separate exception pointers for each thread.
• Exception pointers are shared pointers and must be kept in scope to prevent premature deallocation of the underlying exception object.

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