Last update: 23 February,1998
Eastwood #9
_____________________________________________________________________________
Topic: mutex initialization
Relevant Sections: n/a
Spec: XSH Issue 5
Resolution Request:
-------------------
ISO 9945-1:1996, page 255, lines 513 .. 515 states:
In cases where default mutex attributes are appropriate, the
macro PTHREAD_MUTEX_INITIALIZER can be used to initialize mutexes
that are STATICALLY allocated. (my emphasis)
Was it the intention of the standards committee to preclude
portablility of constructs such as:
int
junk()
{
pthread_mutex_t m;
pthread_mutex_t *pm;
m = PTHREAD_MUTEX_INITIALIZER; /* case 1 */
pm = (pthread_mutex_t *) malloc( ... ); /* case 2 */
if (pm != NULL)
{
*pm = PTHREAD_MUTEX_INITIALIZER;
}
The same question is also asked for PTHREAD_COND_INITIALIZER discussed
on page 261.
Resolution Response
-------------------
We believe that the "intention of the standards committee" was not so much
to preclude the [portable] use of the initializers in assigment statements,
as to allow portable use in initialization statements for various
implementations of the mutex type. E.g.,
pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
The initializers may be array or structure initializers, depending on the
implementation of pthread_mutex_t; and may contain braces and commas which,
in general, would not work in assignment statements. There may be
implementations for which the value of the initializers could be used for
the right hand operand of an assignment, but the standard does not require
this.
Rationale
-------------
None.
Forwarded to Base group: Dec 11 1996
Approved: Feb 1998