pthread_cond_sig_preempt_int_np - Wakes one thread that is
waiting on the specified condition variable (called from
interrupt level only)
pthread_cond_t *cond );
DECthreads POSIX 1003.1c Library (libpthread.so)
Interfaces documented on this reference page conform to
industry standards as follows:
IEEE Std 1003.1c-1995, POSIX System Application Program
Condition variable to be signaled.
This routine wakes one thread waiting on a condition variable.
It can only be called from a software interrupt handler
routine. Calling this routine implies that it might
be possible for a single waiting thread to proceed. Call
this routine when any thread waiting on the specified condition
variable might find its predicate true.
The scheduling policies of the waiting threads determine
which thread is awakened. For policies SCHED_FIFO and
SCHED_RR, a blocked thread is chosen in priority order,
using first-in/first-out (FIFO) within priorities.
You can call this routine when the associated mutex is
either locked or unlocked. Never try to lock a mutex from
an interrupt handler.
This routine allows you to signal a thread from a software
interrupt handler. Do not call this routine from noninterrupt
code. If you want to signal a thread from the normal
interrupt level, use pthread_cond_signal(3).
NOTE: If a waiting thread has a preemptive scheduling policy
and a higher priority than the thread which was running
when the interrupt occurred, then the waiting thread
will preempt the interrupt routine and begin to run immediately.
This is unlike pthread_cond_signal_int_np(3)
which causes the condition variable to be signaled at a
safe point after the interrupt has completed.
pthread_cond_sig_preempt_int_np(3) avoids the possible
latency which pthread_cond_signal_int_np(3) may introduce;
however, a side effect of this is that during the call to
pthread_cond_sig_preempt_int_np(3) other threads may run
if a preemption occurs; thus, once an interrupt routine
calls pthread_cond_sig_preempt_int_np(3) it can no longer
rely on any assumptions of exclusivity or atomicity which
are typically provided by interrupt routines. Furthermore,
once the call to pthread_cond_sig_preempt_int_np(3) is
made, in addition to other threads running, subsequent
interrupts may be delivered at any time as well (that is,
they will not be blocked until the current interrupt completes).
For this reason, it is recommended that
pthread_cond_sig_preempt_int_np(3) be called as the last
statement in the interrupt routine.
If an error condition occurs, this routine returns an
integer value indicating the type of error. Possible
return values are as follows: Successful completion. The
value specified by cond is not a valid condition variable.
Functions: pthread_cond_broadcast(3), pthread_cond_signal(3), pthread_cond_signal_int_np(3), pthread_cond_timedwait(3), pthread_cond_wait(3)
Manuals: Guide to DECthreads and Programmer's Guide
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