Added parameter unique_xids -- use a mutex to ensure unique XIDs

Signed-off-by: Geoff Simmons <geoff@uplex.de>

bin/varnishd/cache_center.c

@@ -77,6 +77,7 @@ DOT acceptor -> start [style=bold,color=green]
 #include "vsha256.h"
 
 static unsigned xids;
+static struct lock xids_mtx;
 
 /*--------------------------------------------------------------------
  * WAIT
@@ -1478,7 +1479,13 @@ cnt_start(struct sess *sp)
 	sp->wrk->acct_tmp.req++;
 
 	/* Assign XID and log */
-	sp->xid = ++xids;				/* XXX not locked */
+        if (params->unique_xids) {
+            Lck_Lock(&xids_mtx);
+            sp->xid = ++xids;
+            Lck_Unlock(&xids_mtx);
+        }
+        else
+            sp->xid = ++xids;
 	WSP(sp, SLT_ReqStart, "%s %s %u", sp->addr, sp->port,  sp->xid);
 
 	/* Borrow VCL reference from worker thread */
@@ -1696,6 +1703,8 @@ CNT_Init(void)
 	srandomdev();
 	srand48(random());
 	xids = random();
+        if (params->unique_xids)
+            Lck_New(&xids_mtx, lck_xids);
 	CLI_AddFuncs(debug_cmds);
 }
 

bin/varnishd/heritage.h

@@ -214,6 +214,8 @@ struct params {
 	double			shortlived;
 
 	struct vre_limits	vre_limits;
+
+        unsigned		unique_xids;
 };
 
 /*

bin/varnishd/locks.h

@@ -49,4 +49,5 @@ LOCK(ban)
 LOCK(vbp)
 LOCK(vbe)
 LOCK(backend)
+LOCK(xids)
 /*lint -restore */

bin/varnishd/mgt_param.c

@@ -974,6 +974,12 @@ static const struct parspec input_parspec[] = {
 		0,
 		"10000", ""},
 
+        { "unique_xids", tweak_bool, &master.unique_xids, 0, 0,
+        	"Ensure that XIDs are uniquely assigned to requests "
+          	"using an additional mutex.\n",
+          	0,
+          	"off", "bool" },
+
 	{ NULL, NULL, NULL }
 };