STREAMS/UX for the HP 9000 Reference Manual

Differences Between STREAMS/UX and System V Release 4 STREAMS

HP-UX Modiﬁcations to STREAMS/UX Utilities

TRYLOCK

The STREAMS/UX TRYLOCK calls the native HP-UX cspinlock

primitive. TRYLOCK has an interrupt priority level parameter, which is

used to raise the priority level and block interrupts which acquire the

spinlock. The SVR4.2 Driver manual says that implementations which do

not require the interrupt level to be raised can ignore this parameter.

STREAMS/UX ignores the parameter on multiprocessor systems since the

HP-UX cspinlock primitive always raises the interrupt level to spl6 while a

spinlock is held. For better performance on uniprocessor systems, the

STREAMS/UX TRYLOCK raises the priority level to the parameter value

instead of acquiring a spinlock.

UNLOCK

The STREAMS/UX UNLOCK calls the native HP-UX spinunlock

primitive. UNLOCK has an interrupt priority level parameter, which is used

to lower the priority level. HP-UX will ignore this parameter on

multiprocessor systems. If the caller is not holding any other spinlocks, the

STREAMS/UX UNLOCK lowers the priority level to the value before the

caller acquired the spinlock. On uniprocessor systems, the STREAMS/UX

UNLOCK lowers the priority level to the parameter value instead of

releasing a spinlock.

weldq and unweldq

STREAMS/UX provides the additional utilities weldq and unweldq to allow

the user to build a pipe-like stream. These utilities are provided because the

programmer is not allowed to modify q_next pointers directly. This

restriction and others are described in more detail in the section called

“HP-UX Changes to STREAMS/UX Data Structures.”