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Thread leaks

Detects when you don’t close threads after use.

Overview

Use this check to detect threads you create using the pthread_create(_:_:_:_:) function without a corresponding call to the pthread_join(_:_:) function. Leaked threads can result in decreased performance and may lead to crashes. Available in Xcode 8 and later.

Leaked thread in C

In the following example, the code creates a thread variable, but doesn’t close it after use:

void *run(){
    pthread_exit(0);
}
pthread_t thread;
pthread_create(&thread, NULL, run, NULL); // Error: thread leak
sleep(1);

Solution

Add a call to the pthread_join(_:_:) function.

void *run(){
    pthread_exit(0);
}
pthread_t thread;
pthread_create(&thread, NULL, run, NULL);
sleep(1);
pthread_join(thread, NULL); // Correct

Alternatively, you can create a detached thread by passing the PTHREAD_CREATE_DETACHED attribute to pthread_create(_:_:_:_:), or calling pthread_detach(_:) on the thread after creation.

See Also

Thread Sanitizer