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Full Discussion: How many semaphores?
Top Forums UNIX for Advanced & Expert Users How many semaphores? Post 302144209 by Watto86 on Tuesday 6th of November 2007 05:14:28 PM
Old 11-06-2007
Quote:
Originally Posted by porter
Would it not be "n-1" where each semaphore is effectively creating the synchronisation for one arrow?
No, I'm afraid not. A process can wait on more than one semaphore, so we don't need that many of them. I am told it is even less than log(n) with base 2 (!), although I cannot prove it.
 

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LEARN ABOUT OPENSOLARIS

semaphore

semaphore.h(3HEAD)						      Headers							semaphore.h(3HEAD)

NAME

       semaphore.h, semaphore - semaphores

SYNOPSIS

       #include <semaphore.h>

DESCRIPTION

       The  <semaphore.h>  header  defines  the sem_t type, used in performing semaphore operations. The semaphore can be implemented using a file
       descriptor, in which case applications are able to open up at least a total of {OPEN_MAX} files and semaphores. The  symbol  SEM_FAILED	is
       defined (see sem_open(3C)).

       Inclusion  of  the <semaphore.h> header can make visible symbols defined in the headers <fcntl.h> and <sys/types.h>. See fcntl.h(3HEAD) and
       types.h(3HEAD).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       fcntl.h(3HEAD),	types.h(3HEAD),  sem_destroy(3C),   sem_getvalue(3C),	sem_init(3C),	sem_open(3C),	sem_post(3C),	sem_timedwait(3C),
       sem_unlink(3C), sem_wait(3C), attributes(5), standards(5)

SunOS 5.11							    5 Feb 2008							semaphore.h(3HEAD)
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