dispatch_once3

Usage

Overview

The dispatch_once() function provides a simple and efficient mechanism to run an initializer exactly once, similar to pthread_once(3). Well designed code hides the use of lazy initialization. For example:

FILE *getlogfile(void)
{
	static dispatch_once_t pred;
	static FILE *logfile;
	dispatch_once(&pred, ^{
		logfile = fopen(MY_LOG_FILE, "a");
	});
	return logfile;
}

Scope of predicate

The variable of type dispatch_once_t must have global or static scope. The result of using this type with automatic or dynamic allocation is undefined.

Fundamentals

The dispatch_once() function is a wrapper around dispatch_once_f().