USOPENPOLLSEMA(3P)					    USOPENPOLLSEMA(3P)

NAME    [Toc]    [Back]

     usopenpollsema - attach a file descriptor to a pollable semaphore

C SYNOPSIS    [Toc]    [Back]

     #include <ulocks.h>

     int usopenpollsema	(usema_t *sema,	mode_t acc);

DESCRIPTION    [Toc]    [Back]

     usopenpollsema attaches a file descriptor to a pollable semaphore.	 The
     returned file descriptor is used when calling poll(2) or select(2)	to
     acquire the semaphore after an unsuccessful uspsema(3P).

     If	the caller is the first	process	to call	usopenpollsema on sema then a
     new semaphore device is allocated (see usema(7M)).	 The user and group id
     of	the semaphore device take on the effective user/group id of the
     caller.  The access mode is set to	acc(see	chmod(2)).  Calls to
     usopenpollsema on the same	semaphore by other processes simply attach to
     the previously allocated device.  They must pass standard Unix file
     permission	tests to be allowed to attach.

     All processes sharing a pollable semaphore, related and unrelated alike,
     must call usopenpollsema before performing	any semaphore operation	on
     sema.

     Forked children must perform their	own usopenpollsema, as the file
     descriptor	inherited from the parent through the fork(2) will not be
     usable.

     A process requires	the file descriptor to call usvsema even if it never
     calls uspsema.

     usopenpollsema will fail if one or	more of	the following are true:

     [EACCES]	   The caller does not have the	required permission to open
		   one or both of the two semaphore device files, /dev/usema
		   and /dev/usemaclone.

     [EACCES]	   The caller is attempting to attach to a previously
		   allocated semaphore device and does not have	the requisite
		   permissions.

     [ENOSPC]	   There are no	more selectable	semaphores available in	the
		   system.  This is configurable up to 255.  See
		   /var/sysgen/master.d/usema.

     [EMFILE]	   The system imposed limit for	open file descriptors per
		   process {OPEN_MAX} has already been reached.

     [ENFILE]	   The system file table has exceeded {NFILE_MAX} concurrently
		   open	files.




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USOPENPOLLSEMA(3P)					    USOPENPOLLSEMA(3P)



     [ENXIO]	   One or both of the two semaphore device files, /dev/usema
		   and /dev/usemaclone,	do not exist, or the device is not
		   configured into the system.

SEE ALSO    [Toc]    [Back]

     chmod(2), open(2),	amalloc(3P), usclosepollsema(3P), usconfig(3P),
     uscpsema(3P), usctlsema(3P), usdumpsema(3P), usfreesema(3P),
     usfreepollsema(3P), usinit(3P), usnewsema(3P), usnewpollsema(3P),
     uspsema(3P), usvsema(3P), usema(7M).

DIAGNOSTICS    [Toc]    [Back]

     Upon successful completion, a file	descriptor is returned.	Otherwise, a
     value of -1 is returned and errno is set to indicate the error.


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