priority-donate-nest.c

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/** Low-priority main thread L acquires lock A.  Medium-priority
   thread M then acquires lock B then blocks on acquiring lock A.
   High-priority thread H then blocks on acquiring lock B.  Thus,
   thread H donates its priority to M, which in turn donates it
   to thread L.
   
   Based on a test originally submitted for Stanford's CS 140 in
   winter 1999 by Matt Franklin <startled@leland.stanford.edu>,
   Greg Hutchins <gmh@leland.stanford.edu>, Yu Ping Hu
   <yph@cs.stanford.edu>.  Modified by arens. */
 
#include <stdio.h>
#include "tests/threads/tests.h"
#include "threads/init.h"
#include "threads/synch.h"
#include "threads/thread.h"
 
struct locks 
  {
    struct lock *a;
    struct lock *b;
  };
 
static thread_func medium_thread_func;
static thread_func high_thread_func;
 
void
test_priority_donate_nest (void) 
{
  struct lock a, b;
  struct locks locks;
 
  /* 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 (&a);
  lock_init (&b);
 
  lock_acquire (&a);
 
  locks.a = &a;
  locks.b = &b;
  thread_create ("medium", PRI_DEFAULT + 1, medium_thread_func, &locks);
  thread_yield ();
  msg ("Low thread should have priority %d.  Actual priority: %d.",
       PRI_DEFAULT + 1, thread_get_priority ());
 
  thread_create ("high", PRI_DEFAULT + 2, high_thread_func, &b);
  thread_yield ();
  msg ("Low thread should have priority %d.  Actual priority: %d.",
       PRI_DEFAULT + 2, thread_get_priority ());
 
  lock_release (&a);
  thread_yield ();
  msg ("Medium thread should just have finished.");
  msg ("Low thread should have priority %d.  Actual priority: %d.",
       PRI_DEFAULT, thread_get_priority ());
}
 
static void
medium_thread_func (void *locks_) 
{
  struct locks *locks = locks_;
 
  lock_acquire (locks->b);
  lock_acquire (locks->a);
 
  msg ("Medium thread should have priority %d.  Actual priority: %d.",
       PRI_DEFAULT + 2, thread_get_priority ());
  msg ("Medium thread got the lock.");
 
  lock_release (locks->a);
  thread_yield ();
 
  lock_release (locks->b);
  thread_yield ();
 
  msg ("High thread should have just finished.");
  msg ("Middle thread finished.");
}
 
static void
high_thread_func (void *lock_) 
{
  struct lock *lock = lock_;
 
  lock_acquire (lock);
  msg ("High thread got the lock.");
  lock_release (lock);
  msg ("High thread finished.");
}