priority-donate-sema.c

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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.");
}