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linuxmacospthreadsmutexcondition-variable

What resources do an unused pthread mutex or condition variable allocate?

Suppose that I have a mutex/condition variable. I initialize (pthread_mutex_init/pthread_cond_init), but never use them (no lock operations, no signal/wait).

Do these unused objects allocate other resources other than the memory they occupy?

(I'm interested in linux and OSX behavior in this regard)

Solution

  • Although POSIX explicitly contemplates that these functions may fail due to a lack of resources (the EAGAIN and ENOMEM error codes), neither the Linux glibc nor OSX implementations of pthread_mutex_init() or pthread_cond_init() allocate any resources. You can see this by direct inspection of the source code:

    The Linux glibc implementation of pthread_mutex_init() is in nptl/pthread_mutex_init.c (see the function __pthread_mutex_init()).

    The Linux glibc implementation of pthread_cond_init() is in nptl/pthread_cond_init.c (see the function __pthread_cond_init()).

    The OSX implementation of pthread_mutex_init() is in libpthread/pthread_mutex.c (see the functions pthread_mutex_init() and _pthread_mutex_init()) and libpthread/internal.h (see the macro _PTHREAD_LOCK_INIT).

    The OSX implementation of pthread_cond_init() is in libpthread/pthread_cond.c (see the functions pthread_cond_init() and _pthread_cond_init()).