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Implement transfer of orphaned donors when releasing lock w/ S

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This commit is contained in:
Themis Demetriades
2024-10-22 20:06:21 +01:00
parent d9b9572631
commit 21cbfc9fe0
1 changed files with 40 additions and 2 deletions
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42
src/threads/synch.c
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@@ -270,15 +270,53 @@ lock_release (struct lock *lock)
ASSERT (lock_held_by_current_thread (lock));
struct thread *current_thread = thread_current ();
struct thread *max_donor = NULL;
struct list orphan_list;
list_init (&orphan_list);
/* Loop through current thread's donors, removing the ones waiting for the
lock being released and keeping track of them (within orphan_list).
Also identifies the highest priority donor thread among them. */
struct list_elem *tail = list_tail (&current_thread->donors_list);
for (struct list_elem *e = list_begin (&current_thread->donors_list);
e != tail; e = e->next)
struct list_elem *e = list_begin (&current_thread->donors_list);
while (e != tail)
{
struct thread *donor = list_entry (e, struct thread, donor_elem);
struct list_elem *next = list_next (e);
/* Excludes donors that aren't waiting for the lock being released,
and tracks the rest. */
if (donor->waiting_lock == lock)
{
list_remove (e);
list_push_back (&orphan_list, e);
/* Identify highest priority donor. */
if (max_donor == NULL || donor->priority > max_donor->priority)
max_donor = donor;
}
e = next;
}
/* If there exists a maximum donor thread waiting for this lock to be
released, transfer the remaining orphaned donors to its donor list. */
if (max_donor != NULL)
{
tail = list_tail (&orphan_list);
e = list_begin (&orphan_list);
while (e != tail)
{
struct list_elem *next = list_next (e);
list_push_back (&max_donor->donors_list, e);
e = next;
}
}
/* Removal of donors to this thread may change its effective priority,
so recalculate. */
thread_recalculate_priority ();
lock->holder = NULL;