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

illumos DDI specific (illumos DDI).

PARAMETERS

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) procedures 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 module'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 qbufcall(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

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;
		            }
	      ...
}