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use a normal binary semaphore for cond to allow a signal that happens before a cond_wait but after a condition check to be received

This commit is contained in:
Chris Copeland 2023-12-10 22:28:29 -08:00
parent c34dc16b1c
commit fe61771778
Signed by: chrisnc
GPG Key ID: 14550DA72485DF30
3 changed files with 18 additions and 6 deletions
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2
examples/water/cond.c
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@ -36,6 +36,8 @@ void oxygen(void)
make_water();
rxn.h -= 2;
rt_mutex_unlock(&rxn.m);
/* To reach this point there will always be >= 2 hydrogens in the
* cond_wait, so neither of these signals is missed. */
rt_cond_signal(&rxn.hdone);
rt_cond_signal(&rxn.hdone);
}

2
include/rt/cond.h
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@ -29,7 +29,7 @@ struct rt_cond
#define RT_COND_INIT(name) \
{ \
.sem = RT_SEM_INIT_MAX(name.sem, 0, 0), \
.sem = RT_SEM_INIT_BINARY(name.sem), \
}
#define RT_COND(name) struct rt_cond name = RT_COND_INIT(name)

20
src/cond.c
View File

@ -11,7 +11,7 @@
void rt_cond_init(struct rt_cond *cond)
{
rt_sem_init_max(&cond->sem, 0, 0);
rt_sem_init_binary(&cond->sem);
}
void rt_cond_signal(struct rt_cond *cond)
@ -32,11 +32,17 @@ void rt_cond_wait(struct rt_cond *cond, struct rt_mutex *mutex)
* signals from higher priority tasks on the same monitor can see
* there is a waiter. */
const int value =
rt_atomic_fetch_sub(&cond->sem.value, 1, RT_ATOMIC_RELAXED);
rt_atomic_fetch_sub(&cond->sem.value, 1, RT_ATOMIC_ACQUIRE);
(void)value;
rt_logf("%s cond wait, new value %d\n", rt_task_name(), value - 1);
if (value > 0)
{
/* The condition was signaled after the caller evaluated the predicate,
* so let the caller re-evaluate it without releasing the mutex. */
return;
}
rt_mutex_unlock(mutex);
rt_logf("%s cond wait, waiting\n", rt_task_name());
@ -57,11 +63,15 @@ bool rt_cond_timedwait(struct rt_cond *cond, struct rt_mutex *mutex,
{
const unsigned long start_tick = rt_tick_count();
const int value =
rt_atomic_fetch_sub(&cond->sem.value, 1, RT_ATOMIC_RELAXED);
rt_atomic_fetch_sub(&cond->sem.value, 1, RT_ATOMIC_ACQUIRE);
(void)value;
rt_logf("%s cond wait, new value %d\n", rt_task_name(), value - 1);
if (value > 0)
{
return true;
}
rt_mutex_unlock(mutex);
if (ticks == 0)