pthread mutex not working correctly

Question

I am currently learning C from MIT\'s Open Courseware course called Practical Programming in C. In discussing race conditions in multithreading, the lecture notes contained

Answer 1

The reason why it works with linux is, because under linux :

#define PTHREAD_MUTEX_INITIALIZER { { 0, 0, 0, 0, 0, { 0 } } }

which is exactly how the mutex is initialized anyway, since it is a .bss-variable.

Under MacOSX, it is some other magic value:

#define PTHREAD_MUTEX_INITIALIZER {_PTHREAD_MUTEX_SIG_init, {0}}
#define _PTHREAD_MUTEX_SIG_init     0x32AAABA7

so it indeed has to be initialized to have it working correctly.

Answer 2

You didn't initialize the mutex. You can either do this:

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

or in the main function, do this:

if ( pthread_mutex_init( &mutex, NULL) != 0 )
    printf( "mutex init failed\n" );