add a write memory barrier before submitting transactions, and a read

mb before reading them to format for log output

src/varnishevent.c

@@ -70,6 +70,7 @@
 #include "vtim.h"
 #include "vpf.h"
 #include "vcs_version.h"
+#include "vmb.h"
 
 #define DEFAULT_CONFIG "/etc/varnishevent.conf"
 
@@ -220,6 +221,7 @@ submit(tx_t *tx)
 {
     CHECK_OBJ_NOTNULL(tx, TX_MAGIC);
     assert(OCCUPIED(tx));
+    VWMB();
     SPSCQ_Enq(tx);
     signal_spscq_ready();
     submitted++;

src/writer.c

@@ -188,7 +188,8 @@ wrt_write(tx_t *tx)
         reopen = 0;
     }
     AZ(pthread_mutex_unlock(&reopen_lock));
-        
+
+    VRMB();
     VSB_clear(os);
     FMT_Format(tx, os);
     VSB_finish(os);