STREAMS/UX for the HP 9000 Reference Manual

STREAMS/UX Multiprocessor Support

Porting SVR4 MP Modules and Drivers to HP-UX

Please read the previous section, “Writing MP Scalable Modules and

Drivers,” before this one. If you compare the previous section to the

SVR4.2 STREAMS manual, you will notice that there are some differences

between SVR4 MP STREAMS and HP-UX MP STREAMS. This section

discusses these differences and describes strategies for porting SVR4 MP

modules and drivers to HP-UX.

Differences between SVR4 and HP-UX MP STREAMS

HP-UX STREAMS provides MP scalability differently from SVR4 MP

STREAMS. There are two main differences. The ﬁrst pertains to which

STREAMS/UX entities run in parallel. SVR4 MP STREAMS executes put

and service routines for the same queue concurrently although only one

instance of a service routine can run at a time. HP-UX, unlike SVR4 MP,

allows the developer to conﬁgure which STREAMS/UX entities run in

parallel. The most parallelism that a STREAMS/UX developer can

conﬁgure is to run entry points for different queues concurrently. Unlike

SVR4 MP, HP-UX only allows one entry point for a queue to run at a time.

The put and service routines for the same queue cannot run in parallel. Also,

multiple instances of a queue's put or service routine cannot execute

concurrently.

The second difference has to do with synchronizing access to module and

driver private data structures. SVR4 MP STREAMS does not provide

protection for private structures. The module or driver code uses spinlocks

to synchronize access. STREAMS/UX provides protection for private

structures. The developer conﬁgures the amount of concurrency for a

module or driver based on the entities with which it shares data structures.

For example, if all instances of a module access the same table, the

programmer can conﬁgure the module so that only one instance runs at a

time.