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.\"
.TH PTHREAD_RWLOCK_INIT 3C "Mar 23, 2005"
.SH NAME
pthread_rwlock_init, pthread_rwlock_destroy \- initialize or destroy read-write
lock object
.SH SYNOPSIS
.LP
.nf
cc -mt [ \fIflag\fR... ] \fIfile\fR... -lpthread [ \fIlibrary\fR... ]
#include <pthread.h>
\fBint\fR \fBpthread_rwlock_init\fR(\fBpthread_rwlock_t *restrict\fR \fIrwlock\fR,
\fBconst pthread_rwlockattr_t *restrict\fR \fIattr\fR);
.fi
.LP
.nf
\fBint\fR \fBpthread_rwlock_destroy\fR(\fBpthread_rwlock_t *\fR\fI*rwlock\fR);
.fi
.LP
.nf
\fBpthread_rwlock_t\fR \fIrwlock\fR=\fBPTHREAD_RWLOCK_INITIALIZER\fR;
.fi
.SH DESCRIPTION
.sp
.LP
The \fBpthread_rwlock_init()\fR function initializes the read-write lock
referenced by \fIrwlock\fR with the attributes referenced by \fIattr\fR. If
\fIattr\fR is NULL, the default read-write lock attributes are used; the
effect is the same as passing the address of a default read-write lock
attributes object. Once initialized, the lock can be used any number of times
without being re-initialized. Upon successful initialization, the state of the
read-write lock becomes initialized and unlocked. Results are undefined if
\fBpthread_rwlock_init()\fR is called specifying an already initialized
read-write lock. Results are undefined if a read-write lock is used without
first being initialized.
.sp
.LP
If the \fBpthread_rwlock_init()\fR function fails, \fIrwlock\fR is not
initialized and the contents of \fIrwlock\fR are undefined.
.sp
.LP
The \fBpthread_rwlock_destroy()\fR function destroys the read-write lock object
referenced by \fIrwlock\fR and releases any resources used by the lock. The
effect of subsequent use of the lock is undefined until the lock is
re-initialized by another call to \fBpthread_rwlock_init()\fR. An
implementation may cause \fBpthread_rwlock_destroy()\fR to set the object
referenced by \fIrwlock\fR to an invalid value. Results are undefined if
\fBpthread_rwlock_destroy()\fR is called when any thread holds \fIrwlock\fR.
Attempting to destroy an uninitialized read-write lock results in undefined
behaviour. A destroyed read-write lock object can be re-initialized using
\fBpthread_rwlock_init()\fR; the results of otherwise referencing the
read-write lock object after it has been destroyed are undefined.
.sp
.LP
In cases where default read-write lock attributes are appropriate, the macro
\fBPTHREAD_RWLOCK_INITIALIZER\fR can be used to initialize read-write locks
that are statically allocated. The effect is equivalent to dynamic
initialization by a call to \fBpthread_rwlock_init()\fR with the parameter
\fIattr\fR specified as NULL, except that no error checks are performed.
.SH RETURN VALUES
.sp
.LP
If successful, the \fBpthread_rwlock_init()\fR and
\fBpthread_rwlock_destroy()\fR functions return \fB0\fR. Otherwise, an error
number is returned to indicate the error.
.SH ERRORS
.sp
.LP
The \fBpthread_rwlock_init()\fR and \fBpthread_rwlock_destroy()\fR functions
will fail if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value specified by \fIattr\fR is invalid.
.RE
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The value specified by \fIrwlock\fR is invalid.
.RE
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp
.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE ATTRIBUTE VALUE
_
Interface Stability Standard
_
MT-Level MT-Safe
.TE
.SH SEE ALSO
.sp
.LP
.BR pthread_rwlock_rdlock (3C),
.BR pthread_rwlock_unlock (3C),
.BR pthread_rwlock_wrlock (3C),
.BR pthread_rwlockattr_init (3C),
.BR attributes (7),
.BR standards (7)
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