Date: Tue, 8 Dec 2009 20:48:06 +0000 (UTC) From: Jilles Tjoelker <jilles@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r200274 - head/lib/libc/gen Message-ID: <200912082048.nB8Km6aP099420@svn.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: jilles Date: Tue Dec 8 20:48:06 2009 New Revision: 200274 URL: http://svn.freebsd.org/changeset/base/200274 Log: sem_init(3): document process shared semaphores and their restrictions Modified: head/lib/libc/gen/sem_init.3 Modified: head/lib/libc/gen/sem_init.3 ============================================================================== --- head/lib/libc/gen/sem_init.3 Tue Dec 8 20:47:10 2009 (r200273) +++ head/lib/libc/gen/sem_init.3 Tue Dec 8 20:48:06 2009 (r200274) @@ -27,7 +27,7 @@ .\" .\" $FreeBSD$ .\" -.Dd February 15, 2000 +.Dd December 8, 2009 .Dt SEM_INIT 3 .Os .Sh NAME @@ -48,8 +48,7 @@ to have the value .Fa value . A non-zero value for .Fa pshared -specifies a shared semaphore that can be used by multiple processes, which this -implementation is not capable of. +specifies a shared semaphore that can be used by multiple processes. .Pp Following a successful call to .Fn sem_init , @@ -78,8 +77,6 @@ argument exceeds .Dv SEM_VALUE_MAX . .It Bq Er ENOSPC Memory allocation error. -.It Bq Er EPERM -Unable to initialize a shared semaphore. .El .Sh SEE ALSO .Xr sem_destroy 3 , @@ -93,16 +90,10 @@ The .Fn sem_init function conforms to .St -p1003.1-96 . -.Pp -This implementation does not support shared semaphores, and reports this fact -by setting -.Va errno -to -.Er EPERM . -This is perhaps a stretch of the intention of -.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. +.Sh BUGS +A sem_t is a pointer to a separately allocated structure, +therefore process shared semaphores only work between related processes +and do not perform very well +(each operation is a system call, +while single-process semaphores only do a system call +if they need to block or wake up a thread).
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200912082048.nB8Km6aP099420>