add a full memory barrier before the main loop in the writer thread,

to ensure that all initializations from the main thread are stored

src/Makefile.am

@@ -31,7 +31,9 @@ varnishevent_SOURCES = \
 	vpf.c \
 	flopen.h \
 	flopen.c \
-	vcs_version.h
+	vcs_version.h \
+	vmb.h \
+	vmb.c
 
 varnishevent_LDADD = \
 	${PTHREAD_LIBS} ${RT_LIBS} ${LIBM} @VARNISH_LIBS@ \

src/vmb.c

+/*-
+ * Copyright (c) 2010 Varnish Software AS
+ * All rights reserved.
+ *
+ * Author: Poul-Henning Kamp <phk@phk.freebsd.dk>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "config.h"
+
+#include <errno.h>
+#include <pthread.h>
+#include <unistd.h>
+
+#include "vas.h"
+#include "vmb.h"
+
+#ifdef VMB_NEEDS_PTHREAD_WORKAROUND_THIS_IS_BAD_FOR_PERFORMANCE
+
+static pthread_mutex_t	mb_mtx;
+static pthread_once_t	mb_mtx_once = PTHREAD_ONCE_INIT;
+
+static void
+vmb_init(void)
+{
+
+	AZ(pthread_mutex_init(&mb_mtx, NULL));
+}
+
+
+void
+vmb_pthread(void)
+{
+
+	AZ(pthread_once(&mb_mtx_once, vmb_init));
+
+	AZ(pthread_mutex_lock(&mb_mtx));
+	AZ(pthread_mutex_unlock(&mb_mtx));
+}
+
+#endif /* VMB_NEEDS_PTHREAD_WORKAROUND_THIS_IS_BAD_FOR_PERFORMANCE */

src/vmb.h

+/*-
+ * Copyright (c) 2010 Varnish Software AS
+ * All rights reserved.
+ *
+ * Author: Poul-Henning Kamp <phk@phk.freebsd.dk>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * Memory barriers
+ *
+ * XXX: It is utterly braindamaged, that no standard facility for this
+ * XXX: is available.  The "just use pthreads locking" excuse does not
+ * XXX: make sense, and does not apply to two unthreaded programs sharing
+ * XXX: a memory segment.
+ */
+
+#ifndef VMB_H_INCLUDED
+#define VMB_H_INCLUDED
+
+#if defined(__FreeBSD__)
+#include <sys/param.h>
+#endif
+
+#if defined(__FreeBSD__) && __FreeBSD_version >= 800058
+
+#include <sys/types.h>
+#include <machine/atomic.h>
+#define VMB()	mb()
+#define VWMB()	wmb()
+#define VRMB()	rmb()
+
+#elif defined(__amd64__) && defined(__GNUC__)
+
+#define VMB()	__asm __volatile("mfence;" : : : "memory")
+#define VWMB()	__asm __volatile("sfence;" : : : "memory")
+#define VRMB()	__asm __volatile("lfence;" : : : "memory")
+
+#elif defined(__arm__)
+
+#define VMB()
+#define VWMB()
+#define VRMB()
+
+#elif defined(__i386__) && defined(__GNUC__)
+
+#define VMB()	__asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
+#define VWMB()	__asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
+#define VRMB()	__asm __volatile("lock; addl $0,(%%esp)" : : : "memory")
+
+#elif defined(__sparc64__) && defined(__GNUC__)
+
+#define VMB()	__asm__ __volatile__ ("membar #MemIssue": : :"memory")
+#define VWMB()	VMB()
+#define VRMB()	VMB()
+
+#else
+
+#define VMB_NEEDS_PTHREAD_WORKAROUND_THIS_IS_BAD_FOR_PERFORMANCE 1
+
+void vmb_pthread(void);
+
+#define VMB()	vmb_pthread()
+#define VWMB()	vmb_pthread()
+#define VRMB()	vmb_pthread()
+
+#endif
+
+#endif /* VMB_H_INCLUDED */

src/writer.c

@@ -44,6 +44,7 @@
 #include "vas.h"
 #include "miniobj.h"
 #include "vsb.h"
+#include "vmb.h"
 
 typedef enum {
     WRT_NOTSTARTED = 0,
@@ -254,7 +255,8 @@ static void
     wrt_nfree_tx = 0;
 
     wrt->state = WRT_RUNNING;
-    
+
+    VMB();
     while (run) {
 	tx = SPSCQ_Deq();
 	if (tx != NULL) {