Sleep for a bit if accept(2) returns EMFILE

Hopefully, this will mitigate pile-ups somewhat and prevent us from
running out of file descriptors, at least as quickly.

See #330.


git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3261 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/cache_acceptor.c

@@ -221,10 +221,20 @@ vca_acct(void *arg)
 			addr = (void*)&addr_s;
 			i = accept(ls->sock, addr, &l);
 			if (i < 0) {
-				if (errno != EAGAIN && errno != ECONNABORTED) {
+				switch (errno) {
+				case EAGAIN:
+				case ECONNABORTED:
+					break;
+				case EMFILE:
 					VSL(SLT_Debug, ls->sock,
-					    "Accept failed errno=%d", errno);
+					    "Too many open files when accept(2)ing. Sleeping.");
+					TIM_sleep(params->accept_fd_holdoff * 1000.0);
+					break;
+				default:
+					VSL(SLT_Debug, ls->sock,
+					    "Accept failed: %s", strerror(errno));
 					/* XXX: stats ? */
+					break;
 				}
 				continue;
 			}

bin/varnishd/heritage.h

@@ -179,6 +179,10 @@ struct params {
 
 	/* Acceptable clockskew with backends */
 	unsigned		clock_skew;
+
+	/* Amount of time to sleep when running out of file
+	   descriptors.  In msecs */
+	unsigned		accept_fd_holdoff;
 };
 
 extern volatile struct params *params;

bin/varnishd/mgt_param.c

@@ -747,6 +747,12 @@ static const struct parspec parspec[] = {
 		"VCL can override this default value for each backend.",
 		0,
 		"400", "ms" },
+	{ "accept_fd_holdoff", tweak_timeout,
+		&master.accept_fd_holdoff, 0,  3600*1000,
+		"If we run out of file descriptors, the accept thread will "
+		"sleep.  This parameter control for how long it will sleep.",
+		EXPERIMENTAL,
+		"50", "ms" },
 	{ "clock_skew", tweak_uint, &master.clock_skew, 0, UINT_MAX,
 		"How much clockskew we are willing to accept between the "
 		"backend and our own clock.",