freezestr, unfreezestr - freeze, thaw the state of a stream
void freezestr(queue_t *q);
void unfreezestr(queue_t *q);
Architecture independent level 1 (DDI/DKI).
Pointer to the message queue to freeze/unfreeze.
DESCRIPTIONfreezestr() 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)