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/* Low priority thread L acquires a lock, then blocks downing a
semaphore. Medium priority thread M then blocks waiting on
the same semaphore. Next, high priority thread H attempts to
acquire the lock, donating its priority to L.
Next, the main thread ups the semaphore, waking up L. L
releases the lock, which wakes up H. H "up"s the semaphore,
waking up M. H terminates, then M, then L, and finally the
main thread.
Written by Godmar Back <gback@cs.vt.edu>. */
#include <stdio.h>
#include "tests/threads/tests.h"
#include "threads/init.h"
#include "threads/synch.h"
#include "threads/thread.h"
struct lock_and_sema
{
struct lock lock;
struct semaphore sema;
};
static thread_func l_thread_func;
static thread_func m_thread_func;
static thread_func h_thread_func;
void
test_priority_donate_sema (void)
{
struct lock_and_sema ls;
/* This test does not work with the MLFQS. */
ASSERT (!thread_mlfqs);
/* Make sure our priority is the default. */
ASSERT (thread_get_priority () == PRI_DEFAULT);
lock_init (&ls.lock);
sema_init (&ls.sema, 0);
thread_create ("low", PRI_DEFAULT + 1, l_thread_func, &ls);
thread_create ("med", PRI_DEFAULT + 3, m_thread_func, &ls);
thread_create ("high", PRI_DEFAULT + 5, h_thread_func, &ls);
sema_up (&ls.sema);
msg ("Main thread finished.");
}
static void
l_thread_func (void *ls_)
{
struct lock_and_sema *ls = ls_;
lock_acquire (&ls->lock);
msg ("Thread L acquired lock.");
sema_down (&ls->sema);
msg ("Thread L downed semaphore.");
lock_release (&ls->lock);
msg ("Thread L finished.");
}
static void
m_thread_func (void *ls_)
{
struct lock_and_sema *ls = ls_;
sema_down (&ls->sema);
msg ("Thread M finished.");
}
static void
h_thread_func (void *ls_)
{
struct lock_and_sema *ls = ls_;
lock_acquire (&ls->lock);
msg ("Thread H acquired lock.");
sema_up (&ls->sema);
lock_release (&ls->lock);
msg ("Thread H finished.");
}
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