Add man pages for the sem_*() functions.

Approved by:	jkh

7 files changed, 516 insertions, 4 deletions

diff --git a/lib/libc_r/man/Makefile.inc b/lib/libc_r/man/Makefile.inc
index b4c9370..fbcbd4e 100644
--- a/lib/libc_r/man/Makefile.inc
+++ b/lib/libc_r/man/Makefile.inc
@@ -4,7 +4,8 @@
 
 .PATH: ${.CURDIR}/man
 
-MAN3+=	pthread_cleanup_pop.3 \
+MAN3+=	pthread_cancel.3 \
+	pthread_cleanup_pop.3 \
 	pthread_cleanup_push.3 \
 	pthread_cond_broadcast.3 \
 	pthread_cond_destroy.3 \
@@ -12,7 +13,6 @@ MAN3+=	pthread_cleanup_pop.3 \
 	pthread_cond_signal.3 \
 	pthread_cond_timedwait.3 \
 	pthread_cond_wait.3 \
-	pthread_cancel.3 \
 	pthread_create.3 \
 	pthread_detach.3 \
 	pthread_equal.3 \
@@ -38,7 +38,16 @@ MAN3+=	pthread_cleanup_pop.3 \
 	pthread_rwlockattr_setpshared.3 \
 	pthread_self.3 \
 	pthread_setspecific.3 \
-	pthread_testcancel.3
+	pthread_testcancel.3 \
+	sem_destroy.3 \
+	sem_getvalue.3 \
+	sem_init.3 \
+	sem_open.3 \
+	sem_post.3 \
+	sem_wait.3
 
 MLINKS+=	pthread_cancel.3 pthread_setcancelstate.3 \
-	pthread_cancel.3 pthread_getcancelstate.3 
+	pthread_cancel.3 pthread_getcancelstate.3 \
+	sem_open.3 sem_close.3 \
+	sem_open.3 sem_unlink.3 \
+	sem_wait.3 sem_trywait.3
diff --git a/lib/libc_r/man/sem_destroy.3 b/lib/libc_r/man/sem_destroy.3
new file mode 100644
index 0000000..770349d
--- /dev/null
+++ b/lib/libc_r/man/sem_destroy.3
@@ -0,0 +1,83 @@
+.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>.
+.\" All rights reserved.
+.\" 
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the
+.\"    distribution.
+.\" 
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\" 
+.\" $FreeBSD$
+.Dd February 15, 2000
+.Dt SEM_DESTROY 3
+.Os
+.Sh NAME
+.Nm sem_destroy
+.Nd destroy an unnamed semaphore
+.Sh SYNOPSIS
+.Fd #include <semaphore.h>
+.Ft int
+.Fn sem_destroy "sem_t *sem"
+.Sh DESCRIPTION
+The
+.Fn sem_destroy
+function destroys the unnamed semaphore pointed to by
+.Fa sem .
+After a successful call to
+.Fn sem_destroy ,
+.Fa sem
+is unuseable until re-initialized by another call to
+.Fn sem_init .
+.Sh RETURN VALUES
+If successful,
+.Fn sem_destroy
+returns 0.  Otherwise, -1 is returned and
+.Va errno
+is set to indicate the type of
+error.
+.Sh ERRORS
+.Fn sem_destroy
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa sem
+points to an invalid semaphore.
+.It Bq Er EBUSY
+There are currently threads blocked on the semaphore that
+.Fa sem
+points to.
+.El
+.Sh SEE ALSO
+.Xr sem_init 3
+.Sh STANDARDS
+.Fn sem_destroy
+conforms to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 1996 Edition.
+.Pp
+POSIX does not define the behavior of
+.Fn sem_destroy
+if called while there are threads blocked on
+.Fa sem ,
+but this implementation is guaranteed to return -1 and set
+.Va errno
+to EBUSY if there are threads blocked on
+.Fa sem .
diff --git a/lib/libc_r/man/sem_getvalue.3 b/lib/libc_r/man/sem_getvalue.3
new file mode 100644
index 0000000..be0cbae
--- /dev/null
+++ b/lib/libc_r/man/sem_getvalue.3
@@ -0,0 +1,77 @@
+.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>.
+.\" All rights reserved.
+.\" 
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the
+.\"    distribution.
+.\" 
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\" 
+.\" $FreeBSD$
+.Dd February 15, 2000
+.Dt SEM_GETVALUE 3
+.Os
+.Sh NAME
+.Nm sem_getvalue
+.Nd get the value of a semaphore
+.Sh SYNOPSIS
+.Fd #include <semaphore.h>
+.Ft int
+.Fn sem_getvalue "sem_t *sem" "int *sval"
+.Sh DESCRIPTION
+The
+.Fn sem_getvalue
+function sets the variable pointed to by
+.Fa sval
+to the current value of the semaphore pointed to by
+.Fa sem ,
+as of the time that the call to
+.Fn sem_getvalue
+is actually run.
+.Sh RETURN VALUES
+If successful,
+.Fn sem_getvalue
+returns 0.  Otherwise, -1 is returned and
+.Va errno
+is set to indicate the type of
+error.
+.Sh ERRORS
+.Fn sem_getvalue
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa sem
+points to an invalid semaphore.
+.El
+.Sh SEE ALSO
+.Xr sem_post 3 ,
+.Xr sem_wait 3 ,
+.Xr sem_trywait 3
+.Sh STANDARDS
+.Fn sem_getvalue
+conforms to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 1996 Edition.
+.Pp
+The value of the semaphore is never negative, even if there are threads blocked
+on the semaphore.  POSIX is somewhat ambiguous in its wording with regard to
+what the value of the semaphore should be if there are blocked waiting threads,
+but this behavior is conformant, given the wording of the specification.
diff --git a/lib/libc_r/man/sem_init.3 b/lib/libc_r/man/sem_init.3
new file mode 100644
index 0000000..059a9c6
--- /dev/null
+++ b/lib/libc_r/man/sem_init.3
@@ -0,0 +1,100 @@
+.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>.
+.\" All rights reserved.
+.\" 
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the
+.\"    distribution.
+.\" 
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\" 
+.\" $FreeBSD$
+.Dd February 15, 2000
+.Dt SEM_INIT 3
+.Os
+.Sh NAME
+.Nm sem_init
+.Nd initialize an unnamed semaphore
+.Sh SYNOPSIS
+.Fd #include <semaphore.h>
+.Ft int
+.Fn sem_init "sem_t *sem" "int pshared" "unsigned int value"
+.Sh DESCRIPTION
+The
+.Fn sem_init
+function initializes the unnamed semaphore pointed to by
+.Fa sem
+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.
+.Pp
+Following a successful call to
+.Fn sem_init ,
+.Fa sem
+can be used as an argument in subsequent calls to
+.Fa sem_wait ,
+.Fa sem_trywait ,
+.Fa sem_post ,
+and
+.Fa sem_destroy .
+.Fa sem
+is no longer valid after a successful call to
+.Fa sem_destroy .
+.Sh RETURN VALUES
+If successful,
+.Fn sem_init
+returns 0.  Otherwise, -1 is returned and
+.Va errno
+is set to indicate the type of
+error.
+.Sh ERRORS
+.Fn sem_init
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa value
+exceeds 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_wait 3 ,
+.Xr sem_trywait 3 ,
+.Xr sem_post 3 ,
+.Xr sem_destroy
+.Sh STANDARDS
+.Fn sem_init
+conforms to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 1996 Edition.
+.Pp
+This implementation does not support shared semaphores, and reports this fact
+by setting
+.Va errno
+to EPERM.  This is perhaps a stretch of the intention of 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.
diff --git a/lib/libc_r/man/sem_open.3 b/lib/libc_r/man/sem_open.3
new file mode 100644
index 0000000..a4729f9
--- /dev/null
+++ b/lib/libc_r/man/sem_open.3
@@ -0,0 +1,80 @@
+.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>.
+.\" All rights reserved.
+.\" 
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the
+.\"    distribution.
+.\" 
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\" 
+.\" $FreeBSD$
+.Dd February 15, 2000
+.Dt SEM_OPEN 3
+.Os
+.Sh NAME
+.Nm sem_open , 
+.Nm sem_close , 
+.Nm sem_unlink
+.Nd named semaphore operations
+.Sh SYNOPSIS
+.Fd #include <semaphore.h>
+.Ft sem_t *
+.Fn sem_open "const char *name" "int oflag" "..."
+.Ft int
+.Fn sem_close "sem_t *sem"
+.Ft int
+.Fn sem_unlink "const char *name"
+.Sh DESCRIPTION
+The
+.Fn sem_open ,
+.Fn sem_close ,
+and
+.Fn sem_unlink
+functions are not supported by this implementation.
+.Sh RETURN VALUES
+.Fn sem_open
+returns SEM_FAILED and sets
+.Va errno
+to indicate an error.
+.Fn sem_close
+and
+.Fn sem_unlink
+return -1 and set
+.Va errno
+to indicate an error.
+.Sh ERRORS
+.Fn sem_open ,
+.Fn sem_close ,
+and
+.Fn sem_unlink
+will fail:
+.Bl -tag -width Er
+.It Bq Er ENOSYS
+Function not supported by this implementation.
+.El
+.Sh STANDARDS
+.Fn sem_open ,
+.Fn sem_close ,
+and
+.Fn sem_unlink
+conform to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 1996 Edition.
diff --git a/lib/libc_r/man/sem_post.3 b/lib/libc_r/man/sem_post.3
new file mode 100644
index 0000000..c578e6d
--- /dev/null
+++ b/lib/libc_r/man/sem_post.3
@@ -0,0 +1,71 @@
+.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>.
+.\" All rights reserved.
+.\" 
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the
+.\"    distribution.
+.\" 
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\" 
+.\" $FreeBSD$
+.Dd February 15, 2000
+.Dt SEM_POST 3
+.Os
+.Sh NAME
+.Nm sem_post
+.Nd increment (unlock) a semaphore
+.Sh SYNOPSIS
+.Fd #include <semaphore.h>
+.Ft int
+.Fn sem_post "sem_t *sem"
+.Sh DESCRIPTION
+The
+.Fn sem_post
+function increments (unlocks) the semaphore pointed to by
+.Fa sem .
+If there are threads blocked on the semaphore when
+.Fn sem_post
+is called, then the highest priority thread that has been blocked the longest on
+the semaphore will be allowed to return from
+.Fn sem_wait .
+.Sh RETURN VALUES
+If successful,
+.Fn sem_post
+returns 0.  Otherwise, -1 is returned and
+.Va errno
+is set to indicate the type of
+error.
+.Sh ERRORS
+.Fn sem_post
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa sem
+points to an invalid semaphore.
+.El
+.Sh SEE ALSO
+.Xr sem_wait 3 ,
+.Xr sem_trywait 3
+.Sh STANDARDS
+.Fn sem_post
+conforms to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 1996 Edition.
diff --git a/lib/libc_r/man/sem_wait.3 b/lib/libc_r/man/sem_wait.3
new file mode 100644
index 0000000..c60c8ee
--- /dev/null
+++ b/lib/libc_r/man/sem_wait.3
@@ -0,0 +1,92 @@
+.\" Copyright (C) 2000 Jason Evans <jasone@canonware.com>.
+.\" All rights reserved.
+.\" 
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer as
+.\"    the first lines of this file unmodified other than the possible
+.\"    addition of one or more copyright notices.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice(s), this list of conditions and the following disclaimer in
+.\"    the documentation and/or other materials provided with the
+.\"    distribution.
+.\" 
+.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
+.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
+.\" LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
+.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\" 
+.\" $FreeBSD$
+.Dd February 15, 2000
+.Dt SEM_WAIT 3
+.Os
+.Sh NAME
+.Nm sem_wait , 
+.Nm sem_trywait
+.Nd decrement (lock) a semaphore
+.Sh SYNOPSIS
+.Fd #include <semaphore.h>
+.Ft int
+.Fn sem_wait "sem_t *sem"
+.Ft int
+.Fn sem_trywait "sem_t *sem"
+.Sh DESCRIPTION
+The
+.Fn sem_wait
+function decrements (locks) the semaphore pointed to by
+.Fa sem ,
+but blocks if the value of
+.Fa sem
+is zero, until the value is non-zero and the value can be decremented.
+.Pp
+The
+.Fn sem_trywait
+function decrements (locks) the semaphore pointed to by
+.Fa sem
+only if the value is non-zero.  Otherwise, the semaphore is not decremented and
+an error is returned.
+.Sh RETURN VALUES
+If successful,
+.Fn sem_wait
+and
+.Fn sem_trywait
+return 0.  Otherwise, -1 is returned and
+.Va errno
+is set to indicate the type of
+error.
+.Sh ERRORS
+.Fn sem_wait
+and
+.Fn sem_trywait
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa sem
+points to an invalid semaphore.
+.El
+.Pp
+Additionally,
+.Fn sem_trywait
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EAGAIN
+The semaphore value was zero, and thus could not be decremented.
+.El
+.Sh SEE ALSO
+.Xr sem_post 3
+.Sh STANDARDS
+.Fn sem_wait
+and
+.Fn sem_trywait
+conform to ISO/IEC 9945-1 ANSI/IEEE
+.Pq Dq Tn POSIX
+Std 1003.1 1996 Edition.