jlaitine commented on code in PR #16194:
URL: https://github.com/apache/nuttx/pull/16194#discussion_r2071307167
##########
sched/semaphore/sem_trywait.c:
##########
@@ -74,29 +77,57 @@ int nxsem_trywait_slow(FAR sem_t *sem)
/* If the semaphore is available, give it to the requesting task */
- semcount = atomic_read(NXSEM_COUNT(sem));
+ if (mutex)
+ {
+ new = nxsched_gettid();
+ }
+
+ old = atomic_read(NXSEM_COUNT(sem));
do
{
- if (semcount <= 0)
+ if (mutex)
{
- leave_critical_section(flags);
- return -EAGAIN;
+ if (NXSEM_MACQUIRED(old))
+ {
+ goto out;
+ }
+ }
+ else
+ {
+ if (old <= 0)
+ {
+ goto out;
+ }
+
+ new = old - 1;
}
}
- while (!atomic_try_cmpxchg_acquire(NXSEM_COUNT(sem),
- &semcount, semcount - 1));
+ while (!atomic_try_cmpxchg_acquire(plock, &old, new));
/* It is, let the task take the semaphore */
ret = nxsem_protect_wait(sem);
if (ret < 0)
{
- atomic_fetch_add(NXSEM_COUNT(sem), 1);
+ if (mutex)
+ {
+ atomic_set(NXSEM_MHOLDER(sem), NXSEM_NO_MHOLDER);
+ }
+ else
+ {
+ atomic_fetch_add(NXSEM_COUNT(sem), 1);
+ }
+
leave_critical_section(flags);
return ret;
}
- nxsem_add_holder(sem);
+ if (!mutex)
Review Comment:
Sem with priority inheritance can surely be a mutex.
I am not sure I understood the question; but you don't need the holder
structure for mutex if the trywait succeeds; and actually can't add it here.
The holder structure is only needed if you get blocked, in which case it is
added for the current holder. This is the same as in sem_wait.
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