How to protect init function of a C based library?

Question

I have written a C based library and for it to work in multi-thread parallely, I create some global mutexes in the init function.

I expect the init function to be called in the main thread before the library APIs are used in multi-thread.

But, if the init function itself is called in multi-thread directly, then it is a problem. Is there a way to protect the init function itself from my library? One way I can think of is to ask the application to create a mutex and protect parallel calls to my init function, but can I protect it from my library itself?

Answer 1

You probably want to use teh default entry point functions.

In windows you can use DllMain to create and destroy your mutexes.

On Linux and probably some other Unixes you can use __attribute__((constructor)) and __attribute__((destructor)) on your entry and exit functions.

In both these case, the functions will be called once on load and unload

Answer 2

POSIX has the pthread_once function

int pthread_once(pthread_once_t *once_control,
              void (*init_routine)(void));

In the linux man page they then have the following instructive example

static pthread_once_t random_is_initialized = PTHREAD_ONCE_INIT;
extern int initialize_random();

int random_function()
{
 (void) pthread_once(&random_is_initialized, initialize_random);
              ... /* Operations performed after initialization. */
}