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).

ARGUMENTS

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. They can be used in the open(9E) and close(9E) procedures in a STREAMS driver or module. qwait() and qwait_sig() atomically exit the inner and outer perimeters associated with the queue, and wait for a thread to leave modules put(9E) or srv(9E) procedures. Upon return they re-enter the inner and outer perimeters.

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() (see condvar(9F)), except that the mutex is replaced by the inner and outer perimeters and the signalling is implicit when a thread leaves the inner perimeter.

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

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;
}
...
}

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