freezestr

, unfreezestr

- freeze, thaw the state of a stream

Synopsis

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

void freezestr(queue_t *q);

void unfreezestr(queue_t *q);

Interface Level

Architecture independent level 1 (DDI/DKI).

Parameters

q

Pointer to the message queue to freeze/unfreeze.

Description

freezestr() freezes the state of the entire stream containing the queue pair q. A frozen stream blocks any thread attempting to enter any open, close, put or service routine belonging to any queue instance in the stream, and blocks any thread currently within the stream if it attempts to put messages onto or take messages off of any queue within the stream (with the sole exception of the caller). Threads blocked by this mechanism remain so until the stream is thawed by a call to unfreezestr().

Drivers and modules must freeze the stream before manipulating the queues directly (as opposed to manipulating them through programmatic interfaces such as getq(9F), putq(9F), putbq(9F), etc.)

Context

These routines may be called from any stream open, close, put or service routine as well as interrupt handlers, callouts and call-backs.

See Also

Writing Device Drivers

STREAMS Programming Guide

Notes

The freezestr() and unfreezestr() functions can have a serious impact on system performance. Their use should be very limited. In most cases, there is no need to use freezestr() and there are usually better ways to accomplish what you need to do than by freezing the stream.

Calling freezestr() to freeze a stream that is already frozen by the caller will result in a single-party deadlock.

The caller of unfreezestr() must be the thread who called freezestr().

STREAMS utility functions such as getq(9F), putq(9F), putbq(9F), and so forth, should not be called by the caller of freezestr() while the stream is still frozen, as they indirectly freeze the stream to ensure atomicity of queue manipulation.