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Full Discussion: Semaphores and File Descriptors
Top Forums UNIX for Dummies Questions & Answers Semaphores and File Descriptors Post 302308632 by Mr_Webster on Sunday 19th of April 2009 08:44:29 PM
Old 04-19-2009
Semaphores and File Descriptors
What is the difference between a file descriptor and a semaphore?

My basic understanding is:

- a file descriptor is a small positive integer that the system uses instead of the file name to identify an open file or socket.

- a semaphore is a variable with a value that indicates the status of a common resource


How do they specifically differ? Some of the definitions I have read, they sound like the same thing.
 

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LEARN ABOUT SUNOS

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(3RT)).

       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	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

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

SunOS 5.10							    10 Sep 2004 						semaphore.h(3HEAD)
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