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.TH PTHREAD_RWLOCK_TRYWRLOCK "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH PROLOG

This manual page is part of the POSIX Programmer's Manual.

The Linux implementation of this interface may differ (consult

the corresponding Linux manual page for details of Linux behavior),

or the interface may not be implemented on Linux.

.SH NAME

pthread_rwlock_trywrlock,

pthread_rwlock_wrlock

\(em lock a read-write lock object for writing

.SH SYNOPSIS

.LP

.nf

#include <pthread.h>

.P

int pthread_rwlock_trywrlock(pthread_rwlock_t *\fIrwlock\fP);

int pthread_rwlock_wrlock(pthread_rwlock_t *\fIrwlock\fP);

.fi

.SH DESCRIPTION

The

\fIpthread_rwlock_trywrlock\fR()

function shall apply a write lock like the

\fIpthread_rwlock_wrlock\fR()

function, with the exception that the function shall fail if any thread

currently holds

.IR rwlock

(for reading or writing).

.P

The

\fIpthread_rwlock_wrlock\fR()

function shall apply a write lock to the read-write lock referenced by

.IR rwlock .

The calling thread acquires the write lock if no other thread (reader

or writer) holds the read-write lock

.IR rwlock .

Otherwise, the thread shall block until it can acquire the lock. The

calling thread may deadlock if at the time the call is made it holds

the read-write lock (whether a read or write lock).

.P

Implementations may favor writers over readers to avoid

writer starvation.

.P

Results are undefined if any of these functions are called with an

uninitialized read-write lock.

.P

If a signal is delivered to a thread waiting for a read-write lock for

writing, upon return from the signal handler the thread resumes waiting

for the read-write lock for writing as if it was not interrupted.

.SH "RETURN VALUE"

The

\fIpthread_rwlock_trywrlock\fR()

function shall return zero if the lock for writing on the read-write

lock object referenced by

.IR rwlock

is acquired. Otherwise, an error number shall be returned to indicate

the error.

.P

If successful, the

\fIpthread_rwlock_wrlock\fR()

function shall return zero; otherwise, an error number shall be

returned to indicate the error.

.SH ERRORS

The

\fIpthread_rwlock_trywrlock\fR()

function shall fail if:

.TP

.BR EBUSY

The read-write lock could not be acquired for writing because it was

already locked for reading or writing.

.P

The

\fIpthread_rwlock_wrlock\fR()

function may fail if:

.TP

.BR EDEADLK

A deadlock condition was detected or the current thread already owns

the read-write lock for writing or reading.

.P

These functions shall not return an error code of

.BR [EINTR] .

.LP

.IR "The following sections are informative."

.SH EXAMPLES

None.

.SH "APPLICATION USAGE"

Applications using these functions may be subject to priority inversion,

as discussed in the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 3.287" ", " "Priority Inversion".

.SH RATIONALE

If an implementation detects that the value specified by the

.IR rwlock

argument to

\fIpthread_rwlock_trywrlock\fR()

or

\fIpthread_rwlock_wrlock\fR()

does not refer to an initialized read-write lock object, it is

recommended that the function should fail and report an

.BR [EINVAL] 

error.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.ad l

.IR "\fIpthread_rwlock_destroy\fR\^(\|)",

.IR "\fIpthread_rwlock_rdlock\fR\^(\|)",

.IR "\fIpthread_rwlock_timedrdlock\fR\^(\|)",

.IR "\fIpthread_rwlock_timedwrlock\fR\^(\|)",

.IR "\fIpthread_rwlock_unlock\fR\^(\|)"

.ad b

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 3.287" ", " "Priority Inversion",

.IR "Section 4.11" ", " "Memory Synchronization",

.IR "\fB<pthread.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the

event of any discrepancy between this version and the original IEEE and

The Open Group Standard, the original IEEE and The Open Group Standard

is the referee document. The original Standard can be obtained online at

http://www.unix.org/online.html .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .