SVR5

freezestr(D3str)

freezestr -- freeze the state of a stream

Synopsis (Not in ODDI)

   #include <sys/types.h>
   #include <sys/stream.h>
   #include <sys/ddi.h>
   
   pl_t freezestr(queue_t *q);

Description

freezestr sets the interrupt priority level to plstr (if the current level is lower than plstr and the implementation requires that interrupts be blocked while the stream is frozen) and freezes the state of the stream containing the queue specified by q. Freezing the stream prevents any further entries into open, close, put, and service procedures on the stream and prevents any messages from being placed on or taken off any queues in the stream (except by the caller of freezestr).

Freezing the stream does not automatically stop all functions that are running within the stream; functions will continue to run until they attempt to perform some operation which changes the state of the stream, at which point they will be forced to wait for the stream to be unfrozen by a call to unfreezestr(D3str).

Arguments

q: Pointer to a message queue.

Return values

freezestr returns the previous interrupt priority level which is typically used in a subsequent call to unfreezestr.

Usage

Drivers and modules must freeze the stream while they manipulate its queues directly. This includes searching the queues and for the duration of any calls to insq(D3str), rmvq(D3str), strqset(D3str), and strqget(D3str).

Context

Base or Interrupt.

Synchronization constraints

Does not block.

Driver-defined basic locks, read/write locks, and sleep locks may be held across calls to this function.

Warnings

freezestr should be used sparingly as it is rarely necessary to freeze a stream (most modules do not need to manipulate their queues directly) and freezing a stream can have a significant negative effect on performance.

Calling freezestr to freeze a stream that is already frozen by the caller will result in deadlock.

Examples

See insq(D3str) for an example of freezestr.

Hardware applicability

All

Version applicability

ddi: 3, 5, 5mp, 6, 6mp, 7, 7mp, 7.1, 7.1mp, 8, 8mp

References

unfreezestr(D3str)