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semaphore: fix bug

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Matheus
2024-09-16 22:55:02 -03:00
parent 5ef9fb0cb3
commit 5e8e54e553
1 changed files with 17 additions and 16 deletions
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kernel-src/lib/semaphore.c
+17 -16
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@@ -33,14 +33,14 @@ static thread_t *get(semaphore_t *sem) {
return thread; return thread;
} }
static void removeself(semaphore_t *sem) { static bool removeself(semaphore_t *sem) {
thread_t *thread = current_thread(); thread_t *thread = current_thread();
// first see if we have been removed already // first see if we have been removed already
if ((sem->head == NULL && sem->tail == NULL) || // no threads in sleep list if ((sem->head == NULL && sem->tail == NULL) || // no threads in sleep list
!((thread->sleepnext != NULL || thread->sleepprev != NULL) || // 2 or more threads in sleep list and we are one of them !((thread->sleepnext != NULL || thread->sleepprev != NULL) || // 2 or more threads in sleep list and we are one of them
(sem->head == thread && sem->tail == thread))) // 1 thread in the sleep list and it is us (sem->head == thread && sem->tail == thread))) // 1 thread in the sleep list and it is us
return; return false;
if (sem->head == thread) { if (sem->head == thread) {
sem->head = thread->sleepnext; sem->head = thread->sleepnext;
@@ -56,6 +56,7 @@ static void removeself(semaphore_t *sem) {
thread->sleepprev = NULL; thread->sleepprev = NULL;
thread->sleepnext = NULL; thread->sleepnext = NULL;
return true;
} }
int semaphore_wait(semaphore_t *sem, bool interruptible) { int semaphore_wait(semaphore_t *sem, bool interruptible) {
@@ -75,8 +76,12 @@ int semaphore_wait(semaphore_t *sem, bool interruptible) {
ret = sched_yield(); ret = sched_yield();
if (ret) { if (ret) {
spinlock_acquire(&sem->lock); spinlock_acquire(&sem->lock);
++sem->i;
removeself(sem); if (removeself(sem))
++sem->i;
else
ret = 0; // we have already been removed in the meantime, so pretend we did not actually get interrupted
spinlock_release(&sem->lock); spinlock_release(&sem->lock);
} }
goto leave; goto leave;
@@ -108,20 +113,16 @@ int semaphore_timedwait(semaphore_t *sem, time_t timeoutusec, bool interruptible
void semaphore_signal(semaphore_t *sem) { void semaphore_signal(semaphore_t *sem) {
bool intstate = interrupt_set(false); bool intstate = interrupt_set(false);
spinlock_acquire(&sem->lock); spinlock_acquire(&sem->lock);
if (++sem->i <= 0) { if (++sem->i <= 0) {
thread_t *thread; thread_t *thread = get(sem);
do { // a thread will always be returned if sem->i <= 0
// wake SOMEONE up. this will *try* to wake up a thread __assert(thread);
// it could wake up none though, as a thread could have been interrupted by a signal
thread = get(sem); // XXX the current method doesn't respect thread priorities
// TODO this is broken sched_wakeup(thread, 0);
// XXX the current method doesn't respect thread priorities
if (thread) {
sched_wakeup(thread, 0);
break;
}
} while (thread);
} }
spinlock_release(&sem->lock); spinlock_release(&sem->lock);
interrupt_set(intstate); interrupt_set(intstate);
} }