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All Rights Reserved. .\" Portions Copyright (c) 2004, Sun Microsystems, Inc. All Rights Reserved. .\" .TH PTHREAD_RWLOCK_TIMEDRDLOCK 3C "April 9, 2016" .SH NAME pthread_rwlock_timedrdlock, pthread_rwlock_reltimedrdlock_np \- lock a read-write lock for reading .SH SYNOPSIS .LP .nf cc \fB-mt\fR [ \fIflag\fR... ] \fIfile\fR... [ \fIlibrary\fR... ] #include #include \fBint\fR \fBpthread_rwlock_timedrdlock\fR(\fBpthread_rwlock_t *restrict\fR \fIrwlock\fR, \fBconst struct timespec *restrict\fR \fIabs_timeout\fR); .fi .LP .nf \fBint\fR \fBpthread_rwlock_reltimedrdlock_np\fR(\fBpthread_rwlock_t *restrict\fR \fIrwlock\fR, \fBconst struct timespec *restrict\fR \fIrel_timeout\fR); .fi .SH DESCRIPTION .LP The \fBpthread_rwlock_timedrdlock()\fR function applies a read lock to the read-write lock referenced by \fIrwlock\fR as in the \fBpthread_rwlock_rdlock\fR(3C) function. If the lock cannot be acquired without waiting for other threads to unlock the lock, this wait will be terminated when the specified timeout expires. The timeout expires when the absolute time specified by \fIabs_timeout\fR passes, as measured by the \fBCLOCK_REALTIME clock\fR (that is, when the value of that clock equals or exceeds \fIabs_timeout\fR), or if the absolute time specified by \fIabs_timeout\fR has already been passed at the time of the call. .sp .LP The \fBpthread_rwlock_reltimedrdlock_np()\fR function is identical to the \fBpthread_rwlock_timedrdlock()\fR function, except that the timeout is specified as a relative time interval. The timeout expires when the time interval specified by \fIrel_timeout\fR passes, as measured by the \fBCLOCK_REALTIME\fR clock, or if the time interval specified by \fIrel_timeout\fR is negative at the time of the call. .sp .LP The resolution of the timeout is the resolution of the \fBCLOCK_REALTIME\fR clock. The \fBtimespec\fR data type is defined in the <\fBtime.h\fR> header. Under no circumstances does either function fail with a timeout if the lock can be acquired immediately. The validity of the timeout parameter need not be checked if the lock can be immediately acquired. .sp .LP If a signal that causes a signal handler to be executed is delivered to a thread blocked on a read-write lock with a call to \fBpthread_rwlock_timedrdlock()\fR or \fBpthread_rwlock_reltimedrdlock_np()\fR, upon return from the signal handler the thread resumes waiting for the lock as if it was not interrupted. .sp .LP The calling thread might deadlock if at the time the call is made it holds a write lock on rwlock. .sp .LP The results are undefined if this function is called with an uninitialized read-write lock. .SH RETURN VALUES .LP The \fBpthread_rwlock_timedrdlock()\fR and \fBpthread_rwlock_reltimedrdlock_np()\fR functions return 0 if the lock for reading on the read-write lock object referenced by \fIrwlock\fR is acquired. Otherwise, an error number is returned to indicate the error. .SH ERRORS .LP The \fBpthread_rwlock_timedrdlock()\fR and \fBpthread_rwlock_reltimedrdlock_np()\fR functions will fail if: .sp .ne 2 .na \fB\fBETIMEDOUT\fR\fR .ad .RS 13n The lock could not be acquired before the specified timeout expired. .RE .sp .LP The \fBpthread_rwlock_timedrdlock()\fR and \fBpthread_rwlock_reltimedrdlock_np()\fR functions may fail if: .sp .ne 2 .na \fB\fBEAGAIN\fR\fR .ad .RS 11n The read lock could not be acquired because the maximum number of read locks for lock would be exceeded. .RE .sp .ne 2 .na \fB\fBEDEADLK\fR\fR .ad .RS 11n The calling thread already holds a write lock on \fIrwlock\fR. .RE .sp .ne 2 .na \fB\fBEINVAL\fR\fR .ad .RS 11n The value specified by \fIrwlock\fR does not refer to an initialized read-write lock object, or the timeout nanosecond value is less than zero or greater than or equal to 1 000 million. .RE .SH ATTRIBUTES .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 See below. _ MT-Level MT-Safe .TE .sp .LP The \fBpthread_rwlock_timedrdlock()\fR function is Standard. The \fBpthread_rwlock_reltimedrdlock_np()\fR is Stable. .SH SEE ALSO .LP .BR pthread_rwlock_destroy (3C), .BR pthread_rwlock_rdlock (3C), .BR pthread_rwlock_timedwrlock (3C), .BR pthread_rwlock_trywrlock (3C), .BR pthread_rwlock_unlock (3C), .BR pthread_rwlock_wrlock (3C), .BR attributes (7), .BR standards (7)