priority donation to a blocked thread.
Idea and code by Godmar Back.
could engage in a variety of activities and notice leaks by checking
the kernel memory statistics.
----
-
-From: "Godmar Back" <godmar@gmail.com>
-Subject: priority donation tests
-To: "Ben Pfaff" <blp@cs.stanford.edu>
-Date: Fri, 3 Mar 2006 11:02:08 -0500
-
-Ben,
-
-it seems the priority donation tests are somewhat incomplete and allow
-incorrect implementations to pass with a perfect score.
-
-We are seeing the following wrong implementations pass all tests:
-
-- Implementations that assume that the priority of a thread waiting on
-a semaphore or condition variable cannot change between when the
-thread was blocked and when it is unblocked. The students implement
-this by doing an insert into an ordered list on block, rather than
-picking the maximum thread on unblock.
-
-Neither of these two cases is detected; do you currently check for
-these mistakes manually?
-
-I also wrote a test case for the second scenario:
-http://people.cs.vt.edu/~gback/pintos/priority-donate-sema.c
-http://people.cs.vt.edu/~gback/pintos/priority-donate-sema.ck
-
From: "Godmar Back" <godmar@gmail.com>
Subject: multiple threads waking up at same clock tick
To: "Ben Pfaff" <blp@cs.stanford.edu>
thus loses the CPU and is moved to the ready queue. Now @var{L}'s
old priority is restored while it is in the ready queue.
+@item Can a thread's priority change while it is blocked?
+
+Yes. While a thread that has acquired lock @var{L} is blocked for any
+reason, its priority can increase by priority donation if a
+higher-priority thread attempts to acquire @var{L}. This case is
+checked by the @code{priority-donate-sema} test.
+
@item Can a thread added to the ready list preempt the processor?
Yes. If a thread added to the ready list has higher priority than the
tests/threads_TESTS = $(addprefix tests/threads/,alarm-single \
alarm-multiple alarm-priority alarm-zero alarm-negative \
priority-change priority-donate-one priority-donate-multiple \
-priority-donate-multiple2 \
-priority-donate-nest priority-fifo priority-preempt priority-sema \
-priority-condvar mlfqs-load-1 mlfqs-load-60 mlfqs-load-avg \
-mlfqs-recent-1 mlfqs-fair-2 mlfqs-fair-20 mlfqs-nice-2 mlfqs-nice-10)
+priority-donate-multiple2 priority-donate-nest priority-donate-sema \
+priority-fifo priority-preempt priority-sema priority-condvar \
+mlfqs-load-1 mlfqs-load-60 mlfqs-load-avg mlfqs-recent-1 mlfqs-fair-2 \
+mlfqs-fair-20 mlfqs-nice-2 mlfqs-nice-10)
# Sources for tests.
tests/threads_SRC = tests/threads/tests.c
tests/threads_SRC += tests/threads/priority-donate-multiple.c
tests/threads_SRC += tests/threads/priority-donate-multiple2.c
tests/threads_SRC += tests/threads/priority-donate-nest.c
+tests/threads_SRC += tests/threads/priority-donate-sema.c
tests/threads_SRC += tests/threads/priority-fifo.c
tests/threads_SRC += tests/threads/priority-preempt.c
tests/threads_SRC += tests/threads/priority-sema.c
Functionality of priority scheduler:
-4 priority-preempt
-4 priority-donate-one
-4 priority-donate-multiple
-4 priority-donate-multiple2
-4 priority-donate-nest
-4 priority-change
+3 priority-preempt
+3 priority-donate-one
+3 priority-donate-multiple
+3 priority-donate-multiple2
+3 priority-donate-nest
+3 priority-donate-sema
+3 priority-change
3 priority-fifo
3 priority-sema
--- /dev/null
+/* 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 (!enable_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.");
+}
--- /dev/null
+# -*- perl -*-
+use strict;
+use warnings;
+use tests::tests;
+check_expected ([<<'EOF']);
+(priority-donate-sema) begin
+(priority-donate-sema) Thread L acquired lock.
+(priority-donate-sema) Thread L downed semaphore.
+(priority-donate-sema) Thread H acquired lock.
+(priority-donate-sema) Thread H finished.
+(priority-donate-sema) Thread M finished.
+(priority-donate-sema) Thread L finished.
+(priority-donate-sema) Main thread finished.
+(priority-donate-sema) end
+EOF
{"priority-donate-multiple", test_priority_donate_multiple},
{"priority-donate-multiple2", test_priority_donate_multiple2},
{"priority-donate-nest", test_priority_donate_nest},
+ {"priority-donate-sema", test_priority_donate_sema},
{"priority-fifo", test_priority_fifo},
{"priority-preempt", test_priority_preempt},
{"priority-sema", test_priority_sema},
extern test_func test_priority_donate_one;
extern test_func test_priority_donate_multiple;
extern test_func test_priority_donate_multiple2;
+extern test_func test_priority_donate_sema;
extern test_func test_priority_donate_nest;
extern test_func test_priority_fifo;
extern test_func test_priority_preempt;
projects / pintos-anon / commitdiff