tis_once(3)tis_once(3)NAMEtis_once - Calls an initialization routine that can be executed by only
one thread, once
SYNOPSIS
#include <tis.h>
int tis_once(
pthread_once_t *once_control,
void (*init_routine)(void) );
LIBRARY
Standard C Library (libc.so, libc.a)
STANDARDS
None
PARAMETERS
Address of a record (control block) that defines the one-time initial‐
ization code. Each one-time initialization routine in static storage
must have its own unique pthread_once_t record. Address of a procedure
that performs the initialization. This routine is called only once,
regardless of the number of times it and its associated once_control
are passed to tis_once(3).
DESCRIPTION
The first call to this routine by a process with a given once_control
calls the init_routine with no arguments. Thereafter, subsequent calls
to tis_once(3) with the same once_control do not call the init_routine.
On return from tis_once(3), it is guaranteed that the initialization
routine has completed.
For example, a mutex or a thread-specific data key must be created
exactly once. In a threaded environment, calling tis_once(3) ensures
that the initialization is serialized across multiple threads.
The once_control argument must be statically initialized using the
PTHREAD_ONCE_INIT macro or by zeroing out the entire structure.
Note If you specify an init_routine that directly or indirectly results
in a recursive call to tis_once(3) and that specifies the same
init_block argument, the recursive call results in a deadlock.
The PTHREAD_ONCE_INIT macro, defined in the <pthread.h> header file,
must be used to initialize a once_control record. Thus, your program
must declare a once_control record as follows:
pthread_once_t once_control= PTHREAD_ONCE_INIT;
Note that it is often easier to simply lock a statically initialized
mutex, check a control option, and perform necessary initialization
(in-line) rather than using tis_once(3). For example, you can code an
“init” routine that begins with the following basic logic:
init() {
static pthread_mutex_t mutex = PTHREAD_MUTEX_INIT;
static int option = FALSE;
tis_mutex_lock(&mutex);
if(!option)
{
option = TRUE;
/* initialize code */
}
tis_mutex_unlock(&mutex);
}
RETURN VALUES
If an error condition occurs, this routine returns an integer value
indicating the type of error. Possible return values are as follows:
Successful completion. Invalid argument.
ERRORS
None
SEE ALSO
Manuals: Guide to DECthreads and Programmer's Guide
tis_once(3)
