From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 25780 invoked by alias); 19 Jan 2010 22:12:40 -0000 Received: (qmail 25770 invoked by uid 22791); 19 Jan 2010 22:12:39 -0000 X-SWARE-Spam-Status: No, hits=-2.4 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS X-Spam-Check-By: sourceware.org Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Tue, 19 Jan 2010 22:12:34 +0000 Received: from int-mx02.intmail.prod.int.phx2.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o0JMCX8l015652 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Tue, 19 Jan 2010 17:12:33 -0500 Received: from host0.dyn.jankratochvil.net (ovpn01.gateway.prod.ext.phx2.redhat.com [10.5.9.1]) by int-mx02.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o0JMCUka032057 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Tue, 19 Jan 2010 17:12:32 -0500 Received: from host0.dyn.jankratochvil.net (localhost [127.0.0.1]) by host0.dyn.jankratochvil.net (8.14.3/8.14.3) with ESMTP id o0JMCU4K032755; Tue, 19 Jan 2010 23:12:30 +0100 Received: (from jkratoch@localhost) by host0.dyn.jankratochvil.net (8.14.3/8.14.3/Submit) id o0JMCTOl032752; Tue, 19 Jan 2010 23:12:29 +0100 Date: Tue, 19 Jan 2010 22:12:00 -0000 From: Jan Kratochvil To: Tom Tromey Cc: gdb-patches@sourceware.org Subject: Re: [patch] testsuite: Fix a race by me - watchthreads-reorder.exp Message-ID: <20100119221228.GA30074@host0.dyn.jankratochvil.net> References: <20091217195026.GA21468@host0.dyn.jankratochvil.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-IsSubscribed: yes Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2010-01/txt/msg00483.txt.bz2 On Thu, 17 Dec 2009 21:27:24 +0100, Tom Tromey wrote: > >>>>> "Jan" == Jan Kratochvil writes: > Jan> + i = pthread_cond_wait (&thread1_tid_cond, &thread1_tid_mutex); > Jan> + assert (i == 0); > > pthread_cond_wait can also spuriously wake up. The usual thing to do is > call it in a loop that checks some condition. Then, have the signalling > thread set the condition before calling pthread_cond_signal. Something > like: > > while (thread1_tid == 0) > pthread_cond_wait (...); > > This is race-free as long as the signalling thread also acquires the > mutex associated with the condition. > > Is there some reason not to do this in this test case? Thanks, I was not proficient in these functions (and have not read the whole manual). OK to check-in? Thanks, Jan gdb/testsuite/ 2010-01-19 Jan Kratochvil * gdb.threads/watchthreads-reorder.c (gdbstop_mutex): Remove. (thread1_func): Protect thread1_tid with thread1_tid_cond by thread1_tid_mutex. Remove gdbstop_mutex handling. (thread2_func): Protect thread2_tid with thread2_tid_cond by thread2_tid_mutex. Remove gdbstop_mutex handling. (main): Move thread1_tid_mutex and thread2_tid_mutex locks before pthread_create. Remove gdbstop_mutex handling. New comment. Replace pthread_cond_wait conditionalizations by while loops. --- a/gdb/testsuite/gdb.threads/watchthreads-reorder.c +++ b/gdb/testsuite/gdb.threads/watchthreads-reorder.c @@ -34,8 +34,6 @@ otherwise. */ #define TIMEOUT (gettid () == getpid() ? 10 : 15) -static pthread_mutex_t gdbstop_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP; - static pid_t thread1_tid; static pthread_cond_t thread1_tid_cond = PTHREAD_COND_INITIALIZER; static pthread_mutex_t thread1_tid_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP; @@ -89,13 +87,14 @@ thread1_func (void *unused) int i; volatile int rwatch_store; + timed_mutex_lock (&thread1_tid_mutex); + + /* THREAD1_TID_MUTEX must be already locked to avoid race. */ thread1_tid = gettid (); + i = pthread_cond_signal (&thread1_tid_cond); assert (i == 0); - - /* Be sure GDB is already stopped before continuing. */ - timed_mutex_lock (&gdbstop_mutex); - i = pthread_mutex_unlock (&gdbstop_mutex); + i = pthread_mutex_unlock (&thread1_tid_mutex); assert (i == 0); rwatch_store = thread1_rwatch; @@ -114,13 +113,14 @@ thread2_func (void *unused) int i; volatile int rwatch_store; + timed_mutex_lock (&thread2_tid_mutex); + + /* THREAD2_TID_MUTEX must be already locked to avoid race. */ thread2_tid = gettid (); + i = pthread_cond_signal (&thread2_tid_cond); assert (i == 0); - - /* Be sure GDB is already stopped before continuing. */ - timed_mutex_lock (&gdbstop_mutex); - i = pthread_mutex_unlock (&gdbstop_mutex); + i = pthread_mutex_unlock (&thread2_tid_mutex); assert (i == 0); rwatch_store = thread2_rwatch; @@ -267,7 +267,8 @@ main (int argc, char **argv) setbuf (stdout, NULL); - timed_mutex_lock (&gdbstop_mutex); + timed_mutex_lock (&thread1_tid_mutex); + timed_mutex_lock (&thread2_tid_mutex); timed_mutex_lock (&terminate_mutex); @@ -306,29 +307,23 @@ main (int argc, char **argv) state_wait (tracer, "T (stopped)"); } - timed_mutex_lock (&thread1_tid_mutex); - timed_mutex_lock (&thread2_tid_mutex); - - /* Let the threads start. */ - i = pthread_mutex_unlock (&gdbstop_mutex); - assert (i == 0); + /* Threads are now waiting at timed_mutex_lock (thread1_tid_mutex) and so + they could not trigger the watchpoints before GDB gets unstopped later. + Threads get resumed at pthread_cond_wait below. Use `while' loops for + protection against spurious pthread_cond_wait wakeups. */ printf ("Waiting till the threads initialize their TIDs.\n"); - if (thread1_tid == 0) + while (thread1_tid == 0) { i = pthread_cond_wait (&thread1_tid_cond, &thread1_tid_mutex); assert (i == 0); - - assert (thread1_tid > 0); } - if (thread2_tid == 0) + while (thread2_tid == 0) { i = pthread_cond_wait (&thread2_tid_cond, &thread2_tid_mutex); assert (i == 0); - - assert (thread2_tid > 0); } printf ("Thread 1 TID = %lu, thread 2 TID = %lu, PID = %lu.\n",