freezestr man page on SmartOS

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       freezestr, unfreezestr - freeze, thaw the state of a stream

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

       void freezestr(queue_t *q);

       void unfreezestr(queue_t *q);

       Architecture independent level 1 (DDI/DKI).

	     Pointer to the message queue to freeze/unfreeze.

       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

       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.)

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

       Writing Device Drivers

       STREAMS Programming Guide

       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.

				 Oct 17, 2000			 FREEZESTR(9F)

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