I was testing some programming with unix sockets and I tested this
program on a Linux machine and there seems to be a problem somewhere :
when I execute the following program "./prog localhost 19 >& log"
the system freeze.
This program just connects 10 clients with the chargen service.
I was logging data to a file on the second drive and I noticed
that both drives were running, the first drive contained the swap
partition.
my config :
Cyrix 120MHz, 16Mb
Linux 2.0.33 #4 Thu Dec 17 21:49:45 MET 1998 i486 unknown
gcc version 2.7.2.2
(this is a rtlinux patched kernel)
Is this normal ?
I have read in the apache docs : htdocs/manual/misc/perf.html
"The most common problem on Linux shows up on heavily-loaded systems where
the whole server will appear to freeze for a couple of minutes at a time,
and then come back to life. This has been traced to a listen() queue
overload - certain Linux implementations have a low value set for the
incoming connection queue which can cause problems. "
Are these problems related ?
On a faster machine you probably should increase MAX_TRIES as the
machine doesn't freeze immediately after starting the program, it
takes about 10-20 seconds to freeze (the drives still continue to
run).
please CC your messages/comments to:
lnxhkr@netscape.net
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <sys/ioctl.h>
#include <string.h>
#include <errno.h>
#include <sys/time.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
/*
* gcc -g -O -Wall -o prog prog.c
* ./prog localhost 19 >& log
*/
#define NICHOST "localhost"
#define MAX(a, b) ((a) > (b) ? (a) : (b))
typedef struct {
char *host;
int port;
int socket;
} ConnectionInfo;
#define NB_CLIENTS 10
#define MAX_TRIES 100000
int
main(argc, argv)
int argc;
char **argv;
{
char *host;
int port;
int i,j,k;
int maxsocket;
ConnectionInfo Cinfo[NB_CLIENTS];
fd_set readfds;
fd_set writefds;
struct timeval tv;
signal(SIGPIPE, SIG_IGN);
if(argc> 1)
host = argv[1];
else
host = NICHOST;
if(argc> 2)
/* chargen 19/tcp
echo 7/tcp */
port = atoi(argv[2]);
else
port = 19;
maxsocket = 0;
for(i=0;i<NB_CLIENTS;i++){
int socket;
Cinfo[i].host = host;
Cinfo[i].port = port;
if( (socket = Connect(&(Cinfo[i]))) < 0) {
printf("error on client %d\n", i);
exit 0;
}
maxsocket = MAX(maxsocket, socket);
/* Make the socket non-blocking */
ioctl(socket, FIONBIO, 1);
}
FD_ZERO(&readfds);
FD_ZERO(&writefds);
for(j=0;j<MAX_TRIES;j++){
/* for(;;){ */
for(i=0;i<NB_CLIENTS;i++){
FD_SET(Cinfo[i].socket, &readfds);
FD_SET(Cinfo[i].socket, &writefds);
}
tv.tv_sec = 2;
tv.tv_usec = 500000;
if(select(maxsocket+1, &readfds, &writefds, NULL, &tv) == -1) {
perror("select");
return 1;
}
for(i=0;i<NB_CLIENTS;i++){
if(FD_ISSET(Cinfo[i].socket, &writefds)){
xsend(Cinfo[i].socket);
}
}
for(i=0;i<NB_CLIENTS;i++){
if(FD_ISSET(Cinfo[i].socket, &readfds)){
if(xrecv(Cinfo[i].socket) < 0)
close(Cinfo[i].socket);
}
}
}
}
int xsend(int s){
char buf[] = "test_test_test_test_test_test_test_test_test_test_";
int r;
r = send(s,buf,strlen(buf),0);
fprintf(stderr,"xsend socket %d\n", s);
return r;
}
int xrecv(int s){
char buf[101];
int r;
r = recv(s,buf,100,0);
if(r>0) {
buf[100] = 0;
fprintf(stderr,"xrecv socket %d: %s\n", s, buf);
} else {
if(r==0){
/* end of communication */
fprintf(stderr,"xrecv socket %d: error:%d\n", s, r);
} else {
/* error */
fprintf(stderr,"xrecv socket %d: error:%d\n", s, r);
}
}
return r;
}
int Connect(ConnectionInfo *Cinfo)
{
register FILE *sfi, *sfo;
register int ch;
struct sockaddr_in sin;
struct hostent *hp;
struct servent *sp;
int s;
char *host;
int nb;
int r;
hp = gethostbyname(Cinfo->host);
if (hp == NULL) {
(void)fprintf(stderr, "prog: %s: ", Cinfo->host);
herror((char *)NULL);
return -1;
}
host = hp->h_name;
s = socket(hp->h_addrtype, SOCK_STREAM, 0);
if (s < 0) {
perror( "socket");
return -2;
}
bzero((caddr_t)&sin, sizeof (sin));
sin.sin_family = hp->h_addrtype;
bcopy(hp->h_addr, (char *)&sin.sin_addr, hp->h_length);
/*sp = getservbyname("chargen", "tcp");
if (sp == NULL) {
errx(1, "chargen/tcp: unknown service");
return -3;
}
*/
sin.sin_port = htons(Cinfo->port) /* htons(80) */ /* sp->s_port */ ;
if (connect(s, (struct sockaddr *)&sin, sizeof(sin)) < 0) {
close(s);
perror( "connect");
return -4;
}
Cinfo->socket = s;
return s;
}
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