Neil Jerram <[email protected]> writes:
> "Julian Graham" <[email protected]> writes:
>
>> Hi Neil,
>>
>>> Based on the synopsis above, I agree that moving step 1 inside the loop
>>> should fix this. In addition, though, I think it would be very good if we
>>> could add a minimal test that currently reproduces the deadlock, and so will
>>> serve to guard against future regressions here. Do you have such a test?
>>
>> I don't -- it seems to be pretty dependent on timing. I noticed it
>> while running my SRFI-18 test suite in a loop, and it took hours to
>> trigger. Any suggestions?
Here is a proposed patch for branch_release-1-8.
Neil
>From 66f3b6c1b043b814663668b5f83210c6e8d1e12d Mon Sep 17 00:00:00 2001
From: Neil Jerram <[email protected]>
Date: Wed, 20 May 2009 21:55:35 +0100
Subject: [PATCH] Remove possible deadlock in scm_join_thread
* libguile/threads.c (scm_join_thread): Always recheck t->exited
before calling block_self again, in case thread t has now exited.
* test-suite/tests/threads.test (joining): New test.
---
libguile/threads.c | 17 +++++++----------
test-suite/tests/threads.test | 34 +++++++++++++++++++++++++++++++++-
2 files changed, 40 insertions(+), 11 deletions(-)
diff --git a/libguile/threads.c b/libguile/threads.c
index fc3e607..3d6df11 100644
--- a/libguile/threads.c
+++ b/libguile/threads.c
@@ -934,17 +934,14 @@ SCM_DEFINE (scm_join_thread, "join-thread", 1, 0, 0,
scm_i_scm_pthread_mutex_lock (&thread_admin_mutex);
t = SCM_I_THREAD_DATA (thread);
- if (!t->exited)
+ while (!t->exited)
{
- while (1)
- {
- block_self (t->join_queue, thread, &thread_admin_mutex, NULL);
- if (t->exited)
- break;
- scm_i_pthread_mutex_unlock (&thread_admin_mutex);
- SCM_TICK;
- scm_i_scm_pthread_mutex_lock (&thread_admin_mutex);
- }
+ block_self (t->join_queue, thread, &thread_admin_mutex, NULL);
+ if (t->exited)
+ break;
+ scm_i_pthread_mutex_unlock (&thread_admin_mutex);
+ SCM_TICK;
+ scm_i_scm_pthread_mutex_lock (&thread_admin_mutex);
}
res = t->result;
diff --git a/test-suite/tests/threads.test b/test-suite/tests/threads.test
index 0146016..34ee7ee 100644
--- a/test-suite/tests/threads.test
+++ b/test-suite/tests/threads.test
@@ -133,4 +133,36 @@
(lambda (n) (set! result (cons n result)))
(lambda (n) (* 2 n))
'(0 1 2 3 4 5))
- (equal? result '(10 8 6 4 2 0)))))))
+ (equal? result '(10 8 6 4 2 0)))))
+
+ ;;
+ ;; thread joining
+ ;;
+
+ (with-test-prefix "joining"
+
+ ;; scm_join_thread has a SCM_TICK in the middle of it, to
+ ;; allow asyncs to run (including signal delivery). We used
+ ;; to have a bug whereby if the joined thread terminated at
+ ;; the same time as the joining thread is in this SCM_TICK,
+ ;; scm_join_thread would not notice and would hang forever.
+ ;; So in this test we are setting up the following sequence of
+ ;; events.
+ ;; T=0 other thread is created and starts running
+ ;; T=2 main thread sets up an async that will sleep for 10 seconds
+ ;; T=2 main thread calls join-thread, which will...
+ ;; T=2 ...call the async, which starts sleeping
+ ;; T=5 other thread finishes its work and terminates
+ ;; T=7 async completes, main thread continues inside join-thread.
+ (pass-if "don't hang when joined thread terminates in SCM_TICK"
+ (let ((other-thread (make-thread sleep 5)))
+ (letrec ((delay-count 10)
+ (aproc (lambda ()
+ (set! delay-count (- delay-count 1))
+ (if (zero? delay-count)
+ (sleep 5)
+ (system-async-mark aproc)))))
+ (sleep 2)
+ (system-async-mark aproc)
+ (join-thread other-thread)))
+ #t))))
--
1.5.6.5
