Should I Use `std::thread::join()` or `std::thread::detach()`?

When to Use std::thread::detach()

Introduction

Multithreading can significantly enhance application performance. In C , std::thread offers a convenient way to create and manage concurrent threads. While std::thread::join() ensures that the main thread waits until a thread completes, the purpose of std::thread::detach() remains unclear.

Detaching vs. Not Detaching

Not Detaching:

Without detach(), the main thread will wait for the created thread to finish before continuing its execution. This approach guarantees that all necessary cleanup is performed before the main thread exits.

Detaching:

Calling detach() informs the system that the main thread no longer needs to wait for the created thread. The detached thread becomes responsible for its own cleanup and will be terminated when all its resources are released.

Implications of Not Detaching

In the destructor of std::thread, std::terminate is called if:

• The thread was not joined (with t.join())
• And was not detached (with t.detach())

Therefore, it's crucial to either join or detach a thread before its destructor is invoked. Failure to do so may cause program termination.

Implications of Detaching

When a program terminates, detached threads are not waited upon. Their execution is suspended, and their thread-local objects are not destructed. Critically, this means that their stack is not unwound, preventing the execution of destructors. This can potentially result in data corruption, file handling issues, or other unexpected behaviors.

Guidelines for Use

Use join:

• When you need to ensure that the main thread waits for the created thread to finish.
• When tasks performed by the thread require cleanup actions.

Use detach:

• When you need flexibility and are prepared to handle thread completion synchronization manually.
• When the created thread does not perform tasks that require extensive cleanup.

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