Updated: April 19, 2023 |
Dynamic package initialization
#include <pthread.h> pthread_once_t once_control = PTHREAD_ONCE_INIT; int pthread_once( pthread_once_t* once_control, void (*init_routine)(void) );
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The pthread_once() function uses the once-control object once_control to determine whether the initialization routine init_routine should be called.
The first call to pthread_once() by any thread in a process, with a given once_control, calls init_routine with no arguments. Subsequent calls of pthread_once() with the same once_control won't call init_routine.
The pthread_once() function isn't a cancellation point. However, if init_routine is a cancellation point and is cancelled, the effect on once_control is as if pthread_once() was never called.
This example shows how you can use once-initialization to initialize a library; both library_entry_point1() and library_entry_point2() need to initialize the library, but that needs to happen only once:
#include <stdio.h> #include <pthread.h> pthread_once_t once_control = PTHREAD_ONCE_INIT; void library_init( void ) { /* initialize the library */ } void library_entry_point1( void ) { pthread_once( &once_control, library_init ); /* do stuff for library_entry_point1... */ } void library_entry_point2( void ) { pthread_once( &once_control, library_init ); /* do stuff for library_entry_point2... */ }
This initializes the library once; if multiple threads call pthread_once(), only one actually enters the library_init() function. The other threads block at the pthread_once() call until library_init() has returned. The pthread_once() function also ensures that library_init() is only ever called once; subsequent calls to the library entry points skip the call to library_init().
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | No |
Signal handler | Yes |
Thread | Yes |