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listen: add process limit option

--- a/sys/man/8/listen

+++ b/sys/man/8/listen

@@ -10,6 +10,8 @@

 .IR trustsrvdir ]

 .RB [ -n

 .IR namespace ]

+.RB [ -p

+.IR maxprocs ]

 .RI [ net ]

 .PP

 .B aux/listen1

@@ -56,6 +58,18 @@

 .B -n

 selects an alternate

 .IR namespace .

+The

+.B -p

+option limits the number of processes that

+.I listen

+spawns to service the connections. If the

+.I maxprocs

+limit is reached,

+.I listen

+will log the event and delay servicing until the number

+of connection processes drops below the limit again. A

+.I maxprocs

+smaller or equal zero means no limit (default).

 Option

 .B -q

 suppresses affirmative log information.

--- a/sys/src/cmd/aux/listen.c

+++ b/sys/src/cmd/aux/listen.c

@@ -22,7 +22,7 @@

 };

 int	readstr(char*, char*, char*, int);

-void	dolisten(char*, char*, int, char*, char*);

+void	dolisten(char*, char*, int, char*, char*, long*);

 void	newcall(int, char*, char*, Service*);

 int 	findserv(char*, char*, Service*, char*);

 int	getserv(char*, char*, Service*);

@@ -33,6 +33,8 @@

 char	listenlog[] = "listen";

+long	procs;

+long	maxprocs;

 int	quiet;

 int	immutable;

 char	*cpu;

@@ -45,7 +47,7 @@

 void

 usage(void)

 {

-	error("usage: aux/listen [-q] [-n namespace] [-d servdir] [-t trustdir]"

+	error("usage: aux/listen [-q] [-n namespace] [-d servdir] [-t trustdir] [-p maxprocs]"

 		" [proto]");

 }

@@ -88,6 +90,7 @@

 	quiet = 0;

 	immutable = 0;

 	argv0 = argv[0];

+	maxprocs = 0;

 	cpu = getenv("cputype");

 	if(cpu == 0)

 		error("can't get cputype");

@@ -105,6 +108,9 @@

 	case 'n':

 		namespace = EARGF(usage());

 		break;

+	case 'p':

+		maxprocs = atoi(EARGF(usage()));

+		break;

 	case 'i':

 		/*

 		 * fixed configuration, no periodic

@@ -161,9 +167,11 @@

 listendir(char *protodir, char *srvdir, int trusted)

 {

 	int ctl, pid, start;

-	char dir[40], err[128];

+	char dir[40], err[128], ds[128];

+	long childs;

 	Announce *a;

 	Waitmsg *wm;

+	int whined;

 	if (srvdir == 0)

 		return;

@@ -201,20 +209,25 @@

 			sleep((pid*10)%200);

+			/* copy to stack */

+			strncpy(ds, a->a, sizeof(ds));

+			whined = a->whined;

+

 			/* a process per service */

-			switch(pid = rfork(RFFDG|RFPROC)){

+			switch(pid = rfork(RFFDG|RFPROC|RFMEM)){

 			case -1:

-				syslog(1, listenlog, "couldn't fork for %s", a->a);

+				syslog(1, listenlog, "couldn't fork for %s", ds);

 				break;

 			case 0:

+				childs = 0;

 				for(;;){

-					ctl = announce(a->a, dir);

+					ctl = announce(ds, dir);

 					if(ctl < 0) {

 						errstr(err, sizeof err);

-						if (!a->whined)

+						if (!whined)

 							syslog(1, listenlog,

 							   "giving up on %s: %r",

-							a->a);

+							ds);

 						if(strstr(err, "address in use")

 						    != nil)

 							exits("addr-in-use");

@@ -221,7 +234,7 @@

 						else

 							exits("ctl");

 					}

-					dolisten(proto, dir, ctl, srvdir, a->a);

+					dolisten(proto, dir, ctl, srvdir, ds, &childs);

 					close(ctl);

 				}

 			default:

@@ -377,14 +390,57 @@

 }

 void

-dolisten(char *proto, char *dir, int ctl, char *srvdir, char *dialstr)

+dolisten(char *proto, char *dir, int ctl, char *srvdir, char *dialstr, long *pchilds)

 {

 	Service s;

-	char ndir[40];

-	int nctl, data;

+	char ndir[40], wbuf[64];

+	int nctl, data, wfd, nowait;

 	procsetname("%s %s", dir, dialstr);

+

+	wfd = -1;

+	nowait = RFNOWAIT;

+	if(pchilds && maxprocs > 0){

+		snprint(wbuf, sizeof(wbuf), "/proc/%d/wait", getpid());

+		if((wfd = open(wbuf, OREAD)) >= 0)

+			nowait = 0;

+	}

+

 	for(;;){

+		if(!nowait){

+			static int hit = 0;

+			Dir *d;

+

+			/*

+			 *  check for exited subprocesses

+			 */

+			if(procs >= maxprocs || (*pchilds % 8) == 0)

+				while(*pchilds > 0){

+					d = dirfstat(wfd);

+					if(d == nil || d->length == 0){

+						free(d);

+						break;

+					}

+					free(d);

+					if(read(wfd, wbuf, sizeof(wbuf)) > 0){

+						adec(&procs);

+						pchilds[0]--;

+					}

+				}

+

+			if(procs >= maxprocs){

+				if(!quiet && !hit)

+					syslog(1, listenlog, "%s: process limit of %ld reached",

+						proto, maxprocs);

+				if(hit < 8)

+					hit++;

+				sleep(10<<hit);

+				continue;

+			} 

+			if(hit > 0)

+				hit--;

+		}

+

 		/*

 		 *  wait for a call (or an error)

 		 */

@@ -392,6 +448,8 @@

 		if(nctl < 0){

 			if(!quiet)

 				syslog(1, listenlog, "listen: %r");

+			if(wfd >= 0)

+				close(wfd);

 			return;

 		}

@@ -398,7 +456,7 @@

 		/*

 		 *  start a subprocess for the connection

 		 */

-		switch(rfork(RFFDG|RFPROC|RFNOWAIT|RFENVG|RFNAMEG|RFNOTEG)){

+		switch(rfork(RFFDG|RFPROC|RFMEM|RFENVG|RFNAMEG|RFNOTEG|nowait)){

 		case -1:

 			reject(nctl, ndir, "host overloaded");

 			close(nctl);

@@ -423,10 +481,16 @@

 			fprint(nctl, "keepalive");

 			close(ctl);

 			close(nctl);

+			if(wfd >= 0)

+				close(wfd);

 			newcall(data, proto, ndir, &s);

 			exits(0);

 		default:

 			close(nctl);

+			if(nowait)

+				break;

+			ainc(&procs);

+			pchilds[0]++;

 			break;

 		}

 	}

-- 

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