Do you mean {} for the entire initializer? That would not necessarily work because PTHREAD_MUTEX_INITIALIZER is not guaranteed to be the same as zero-initialization. Or do you mean {} instead of pthread_t()? The would not necessarily work either because pthread_t is not guaranteed to be a structure; POSIX allows it to be an arithmetic type (and even required it to be arithmetic prior to Issue 6). The code as currently written complies rigidly with the C++03 and POSIX specs regardless of the underlying types involved.