-#include "synch.h"
-#include "interrupt.h"
-#include "lib.h"
-#include "thread.h"
-
-/* One thread in a list. */
-struct thread_elem
- {
- list_elem elem;
- struct thread *thread;
- };
+/* This file is derived from source code for the Nachos
+ instructional operating system. The Nachos copyright notice
+ is reproduced in full below. */
+
+/* Copyright (c) 1992-1996 The Regents of the University of California.
+ All rights reserved.
+
+ Permission to use, copy, modify, and distribute this software
+ and its documentation for any purpose, without fee, and
+ without written agreement is hereby granted, provided that the
+ above copyright notice and the following two paragraphs appear
+ in all copies of this software.
+
+ IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO
+ ANY PARTY FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR
+ CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF THIS SOFTWARE
+ AND ITS DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA
+ HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+ THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY
+ WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN "AS IS"
+ BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
+ PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
+ MODIFICATIONS.
+*/
+
+#include "threads/synch.h"
+#include <stdio.h>
+#include <string.h>
+#include "threads/interrupt.h"
+#include "threads/thread.h"
/* Initializes semaphore SEMA to VALUE and names it NAME (for
debugging purposes only). A semaphore is a nonnegative
list_init (&sema->waiters);
}
-/* Waits for SEMA's value to become positive and then
- atomically decrements it.
+/* Down or "P" operation on a semaphore. Waits for SEMA's value
+ to become positive and then atomically decrements it.
This function may sleep, so it must not be called within an
interrupt handler. This function may be called with
old_level = intr_disable ();
while (sema->value == 0)
{
- struct thread_elem te;
- te.thread = thread_current ();
- list_push_back (&sema->waiters, &te.elem);
- thread_sleep ();
+ list_push_back (&sema->waiters, &thread_current ()->elem);
+ thread_block ();
}
sema->value--;
intr_set_level (old_level);
}
-/* Increments SEMA's value. Wakes up one thread of those waiting
- for SEMA, if any.
+/* Up or "V" operation on a semaphore. Increments SEMA's value
+ and wakes up one thread of those waiting for SEMA, if any.
This function may be called from an interrupt handler. */
void
old_level = intr_disable ();
if (!list_empty (&sema->waiters))
- thread_wake (list_entry (list_pop_front (&sema->waiters),
- struct thread_elem, elem)->thread);
+ thread_unblock (list_entry (list_pop_front (&sema->waiters),
+ struct thread, elem));
sema->value++;
intr_set_level (old_level);
}
return sema->name;
}
-static void
-sema_test_helper (void *sema_)
-{
- struct semaphore *sema = sema_;
- int i;
-
- for (i = 0; i < 10; i++)
- {
- sema_down (&sema[0]);
- sema_up (&sema[1]);
- }
-}
+static void sema_test_helper (void *sema_);
/* Self-test for semaphores that makes control "ping-pong"
- between a pair of threads. Insert calls to printk() to see
+ between a pair of threads. Insert calls to printf() to see
what's going on. */
void
sema_self_test (void)
{
- struct thread *thread;
struct semaphore sema[2];
int i;
+ printf ("Testing semaphores...");
sema_init (&sema[0], 0, "ping");
sema_init (&sema[1], 0, "pong");
- thread = thread_create ("sema-test", sema_test_helper, &sema);
+ thread_create ("sema-test", PRI_DEFAULT, sema_test_helper, &sema);
for (i = 0; i < 10; i++)
{
sema_up (&sema[0]);
sema_down (&sema[1]);
}
+ printf ("done.\n");
+}
+
+/* Thread function used by sema_self_test(). */
+static void
+sema_test_helper (void *sema_)
+{
+ struct semaphore *sema = sema_;
+ int i;
+
+ for (i = 0; i < 10; i++)
+ {
+ sema_down (&sema[0]);
+ sema_up (&sema[1]);
+ }
}
\f
/* Initializes LOCK and names it NAME (for debugging purposes).
ASSERT (lock != NULL);
ASSERT (name != NULL);
- strlcpy (lock->name, name, sizeof lock->name);
lock->holder = NULL;
sema_init (&lock->semaphore, 1, name);
}
/* Releases LOCK, which must be owned by the current thread.
An interrupt handler cannot acquire a lock, so it does not
- make sense to try to signal a condition variable within an
- interrupt handler. */
+ make sense to try to release a lock within an interrupt
+ handler. */
void
lock_release (struct lock *lock)
{
{
ASSERT (lock != NULL);
- return lock->name;
+ return sema_name (&lock->semaphore);
}
\f
/* One semaphore in a list. */
struct semaphore_elem
{
- list_elem elem;
- struct semaphore semaphore;
+ struct list_elem elem; /* List element. */
+ struct semaphore semaphore; /* This semaphore. */
};
/* Initializes condition variable COND and names it NAME. A
}
/* Atomically releases LOCK and waits for COND to be signaled by
- some other piece of code. After COND is signalled, LOCK is
+ some other piece of code. After COND is signaled, LOCK is
reacquired before returning. LOCK must be held before calling
this function.
The monitor implemented by this function is "Mesa" style, not
- "Hoare" style. That is, sending a signal is not atomic with
- delivering it. Thus, typically the caller must recheck the
- condition after the wait completes and, if necessary, wait
+ "Hoare" style, that is, sending and receiving a signal are not
+ an atomic operation. Thus, typically the caller must recheck
+ the condition after the wait completes and, if necessary, wait
again.
A given condition variable is associated with only a single
- lock, but one lock may be be associated with any number of
+ lock, but one lock may be associated with any number of
condition variables. That is, there is a one-to-many mapping
from locks to condition variables.
projects / pintos-anon / blobdiff