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Refactor donate_priority to include comments explaining its purpose and logic w/ S

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Themis Demetriades
2024-10-22 21:15:30 +01:00
parent 78c6fd36e3
commit 7aec2e6862
1 changed files with 9 additions and 0 deletions
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9
src/threads/synch.c
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@@ -194,16 +194,25 @@ lock_init (struct lock *lock)
sema_init (&lock->semaphore, 1); sema_init (&lock->semaphore, 1);
} }
/* Allows for the donor to donate its priority to donee, iteratively
propagating the donation in the case of chains in the wait-for graph.
Also keeps track of the donation by updating the donors list. */
static void static void
donate_priority (struct thread *donor, struct thread *donee) { donate_priority (struct thread *donor, struct thread *donee) {
list_push_back (&donee->donors_list, &donor->donor_elem); list_push_back (&donee->donors_list, &donor->donor_elem);
while (donee != NULL) while (donee != NULL)
{ {
/* Stop propagation of donation once a donee is reached that has
a higher effective priority (as its donees can't have less
priority than that being donated). */
if (donor->priority <= donee->priority) if (donor->priority <= donee->priority)
break; break;
donee->priority = donor->priority; donee->priority = donor->priority;
/* Also stop propagation of donation once a donee is reached with
no donees of its own (sink node in WFG). */
if (donee->waiting_lock == NULL) if (donee->waiting_lock == NULL)
donee = NULL; donee = NULL;
else else