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sem_init(3): document process shared semaphores and their restrictions

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This commit is contained in:
Jilles Tjoelker 2009-12-08 20:48:06 +00:00
parent 9d7031a6d6
commit 461e296c49
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=200274
1 changed files with 9 additions and 18 deletions
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27
lib/libc/gen/sem_init.3
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@ -27,7 +27,7 @@
.\" .\"
.\" $FreeBSD$ .\" $FreeBSD$
.\" .\"
.Dd February 15, 2000 .Dd December 8, 2009
.Dt SEM_INIT 3 .Dt SEM_INIT 3
.Os .Os
.Sh NAME .Sh NAME
@ -48,8 +48,7 @@ to have the value
.Fa value . .Fa value .
A non-zero value for A non-zero value for
.Fa pshared .Fa pshared
specifies a shared semaphore that can be used by multiple processes, which this specifies a shared semaphore that can be used by multiple processes.
implementation is not capable of.
.Pp .Pp
Following a successful call to Following a successful call to
.Fn sem_init , .Fn sem_init ,
@ -78,8 +77,6 @@ argument exceeds
.Dv SEM_VALUE_MAX . .Dv SEM_VALUE_MAX .
.It Bq Er ENOSPC .It Bq Er ENOSPC
Memory allocation error. Memory allocation error.
.It Bq Er EPERM
Unable to initialize a shared semaphore.
.El .El
.Sh SEE ALSO .Sh SEE ALSO
.Xr sem_destroy 3 , .Xr sem_destroy 3 ,
@ -93,16 +90,10 @@ The
.Fn sem_init .Fn sem_init
function conforms to function conforms to
.St -p1003.1-96 . .St -p1003.1-96 .
.Pp .Sh BUGS
This implementation does not support shared semaphores, and reports this fact A sem_t is a pointer to a separately allocated structure,
by setting therefore process shared semaphores only work between related processes
.Va errno and do not perform very well
to (each operation is a system call,
.Er EPERM . while single-process semaphores only do a system call
This is perhaps a stretch of the intention of if they need to block or wake up a thread).
.Tn POSIX ,
but is
compliant, with the caveat that
.Fn sem_init
always reports a permissions error when an attempt to create a shared semaphore
is made.