priority-donate-chain.c

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/** The main thread set its priority to PRI_MIN and creates 7 threads 
   (thread 1..7) with priorities PRI_MIN + 3, 6, 9, 12, ...
   The main thread initializes 8 locks: lock 0..7 and acquires lock 0.
 
   When thread[i] starts, it first acquires lock[i] (unless i == 7.)
   Subsequently, thread[i] attempts to acquire lock[i-1], which is held by
   thread[i-1], except for lock[0], which is held by the main thread.
   Because the lock is held, thread[i] donates its priority to thread[i-1],
   which donates to thread[i-2], and so on until the main thread
   receives the donation.
 
   After threads[1..7] have been created and are blocked on locks[0..7],
   the main thread releases lock[0], unblocking thread[1], and being
   preempted by it.
   Thread[1] then completes acquiring lock[0], then releases lock[0],
   then releases lock[1], unblocking thread[2], etc.
   Thread[7] finally acquires & releases lock[7] and exits, allowing 
   thread[6], then thread[5] etc. to run and exit until finally the 
   main thread exits.
 
   In addition, interloper threads are created at priority levels
   p = PRI_MIN + 2, 5, 8, 11, ... which should not be run until the 
   corresponding thread with priority p + 1 has finished.
  
   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"
 
#define NESTING_DEPTH 8
 
struct lock_pair
  {
    struct lock *second;
    struct lock *first;
  };
 
static thread_func donor_thread_func;
static thread_func interloper_thread_func;
 
void
test_priority_donate_chain (void) 
{
  int i;  
  struct lock locks[NESTING_DEPTH - 1];
  struct lock_pair lock_pairs[NESTING_DEPTH];
 
  /* This test does not work with the MLFQS. */
  ASSERT (!thread_mlfqs);
 
  thread_set_priority (PRI_MIN);
 
  for (i = 0; i < NESTING_DEPTH - 1; i++)
    lock_init (&locks[i]);
 
  lock_acquire (&locks[0]);
  msg ("%s got lock.", thread_name ());
 
  for (i = 1; i < NESTING_DEPTH; i++)
    {
      char name[16];
      int thread_priority;
 
      snprintf (name, sizeof name, "thread %d", i);
      thread_priority = PRI_MIN + i * 3;
      lock_pairs[i].first = i < NESTING_DEPTH - 1 ? locks + i: NULL;
      lock_pairs[i].second = locks + i - 1;
 
      thread_create (name, thread_priority, donor_thread_func, lock_pairs + i);
      msg ("%s should have priority %d.  Actual priority: %d.",
          thread_name (), thread_priority, thread_get_priority ());
 
      snprintf (name, sizeof name, "interloper %d", i);
      thread_create (name, thread_priority - 1, interloper_thread_func, NULL);
    }
 
  lock_release (&locks[0]);
  msg ("%s finishing with priority %d.", thread_name (),
                                         thread_get_priority ());
}
 
static void
donor_thread_func (void *locks_) 
{
  struct lock_pair *locks = locks_;
 
  if (locks->first)
    lock_acquire (locks->first);
 
  lock_acquire (locks->second);
  msg ("%s got lock", thread_name ());
 
  lock_release (locks->second);
  msg ("%s should have priority %d. Actual priority: %d", 
        thread_name (), (NESTING_DEPTH - 1) * 3,
        thread_get_priority ());
 
  if (locks->first)
    lock_release (locks->first);
 
  msg ("%s finishing with priority %d.", thread_name (),
                                         thread_get_priority ());
}
 
static void
interloper_thread_func (void *arg_ UNUSED)
{
  msg ("%s finished.", thread_name ());
}
 
// vim: sw=2