qwait(9F)						   Kernel Functions for Drivers 						 qwait(9F)

NAME

       qwait, qwait_sig - STREAMS wait routines

SYNOPSIS

       #include <sys/stream.h>
       #include <sys/ddi.h>

       void qwait(queue_t *q);

       int qwait_sig(queue_t *q);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI).

PARAMETERS

       qp    Pointer to the queue that is being opened or closed.

DESCRIPTION

       qwait()	and qwait_sig() are used to wait for a message to arrive to the put(9E) or srv(9E) procedures. qwait() and qwait_sig() can also be
       used to wait for qbufcall(9F) or qtimeout(9F) callback procedures to execute. These routines can be used in the open(9E) and close(9E) pro-
       cedures in a STREAMS driver or module.

       The  thread that calls close() does not necessarily have the ability to receive signals, particularly when called by exit(2). In this case,
       qwait_sig() behaves exactly as qwait(). Driver writers may use ddi_can_receive_sig(9F) to determine when this is  the  case,  and,  if  so,
       arrange some means to avoid blocking indefinitely (for example, by using qtimeout(9F).

       qwait()	and  qwait_sig() atomically exit the inner and outer perimeters associated with the queue, and wait for a thread to leave the mod-
       ule's put(9E), srv(9E), or qbufcall(9F) / qtimeout(9F) callback procedures. Upon return they re-enter the inner and outer perimeters.

       This can be viewed as there being an implicit wakeup when a thread leaves a put(9E) or srv(9E) procedure or after a qtimeout(9F)  or  qbuf-
       call(9F) callback procedure has been run in the same perimeter.

       qprocson(9F) must be called before calling qwait() or qwait_sig().

       qwait()	is not interrupted by a signal, whereas qwait_sig() is interrupted by a signal. qwait_sig() normally returns non-zero, and returns
       zero when the waiting was interrupted by a signal.

       qwait() and qwait_sig() are similar to cv_wait() and cv_wait_sig() except that the mutex is replaced by the inner and outer perimeters  and
       the signalling is implicit when a thread leaves the inner perimeter. See condvar(9F).

RETURN VALUES

       0    For qwait_sig(), indicates that the condition was not necessarily signaled, and the function returned because a signal was pending.

CONTEXT

       These functions can only be called from an open(9E) or close(9E) routine.

EXAMPLES

       Example 1 Using qwait()

       The  open  routine  sends  down a T_INFO_REQ message and waits for the T_INFO_ACK. The arrival of the T_INFO_ACK is recorded by resetting a
       flag in the unit structure (WAIT_INFO_ACK). The example assumes that the module is D_MTQPAIR or D_MTPERMOD.

	 xxopen(qp, ...)
		queue_t *qp;
	 {
		    struct xxdata *xx;
		     /* Allocate xxdata structure */
		qprocson(qp);
		/* Format T_INFO_ACK in mp */
		putnext(qp, mp);
		xx->xx_flags |= WAIT_INFO_ACK;
		while (xx->xx_flags & WAIT_INFO_ACK)
			       qwait(qp);
		    return(0);
	 }
	 xxrput(qp, mp)
		queue_t *qp;
		mblk_t *mp;
	 {
		struct xxdata *xx = (struct xxdata *)q->q_ptr;

		    ...

		    case T_INFO_ACK:
			       if (xx->xx_flags & WAIT_INFO_ACK) {
				      /* Record information from info ack */
				      xx->xx_flags &= ~WAIT_INFO_ACK;
				      freemsg(mp);
				      return;
			       }

		    ...
	 }

SEE ALSO

       close(9E), open(9E), put(9E), srv(9E), condvar(9F), ddi_can_receive_sig(9F), mt-streams(9F), qbufcall(9F), qprocson(9F), qtimeout(9F)

       STREAMS Programming Guide

       Writing Device Drivers

SunOS 5.11							    15 Dec 2003 							 qwait(9F)