Re: accept does not return in case a signal arrives

Re: accept does not return in case a signal arrives

[Alan Cox]

On Mer, 2004-11-03 at 13:26, Gerrit Bruchhäuser wrote:
> Dear Kernel-team,
> 
> on Linux, 'accept' system call does not return in case I send SIGTERM to 
> my application; while it does on OSF-Alpha.

signal() may or may not interrupt some system calls. Use sigaction if
you want to force a given behaviour (and write portable code)

accept does not return in case a signal arrives

[Gerrit Bruchhäuser]

Dear Kernel-team,

on Linux, 'accept' system call does not return in case I send SIGTERM to 
my application; while it does on OSF-Alpha.

Given the following sample:

,----[ main.cc ]
| #include <sys/types.h>
| #include <sys/socket.h>
| #include <errno.h>
| #include <string.h>
| #include <stdio.h>
| #include <stdlib.h>
| #include <resolv.h>
| #include <signal.h>
|
| #define CHECK_RET_M(arg, x) \
|   if (-1 == (x) && errno != EINTR) { \
|      printf("System call '%s' failed: %s\n", #arg, strerror(errno)); \
|      exit(1); \
|   }
|
| typedef struct sockaddr SA;
|
| static void TermHandler(int signu)
| {
|    // Nothing
| }
|
| int main(int argc, char *argv[])
| {
|   // Create signal handler 4 SIGTERM
|   signal(SIGTERM, &TermHandler);
|
|   // Create listening socket...
|   // argv[1] will be the port number!
|   int port = atoi(argv[1]);
|   int listen_fd = socket(AF_INET, SOCK_STREAM, 0); CHECK_RET_M(socket, 
listen_fd);
|
|   struct sockaddr_in servaddr;
|   bzero((char *) &servaddr, sizeof(servaddr));
|   servaddr.sin_family      = AF_INET;
|   servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
|   servaddr.sin_port        = htons(port);
|
|   // Bind the socket and switch its state to 'listen'...
|   int r = bind(listen_fd, (SA *) &servaddr, sizeof(servaddr)); 
CHECK_RET_M(bind, r);
|   int backlog = 1000;
|   r = listen(listen_fd, backlog); CHECK_RET_M(listen, r);
|
|   // Wait until client tries to connect...
|   struct sockaddr_in cliaddr;
|   socklen_t clilen = (socklen_t) sizeof(cliaddr);
|   int conn_fd = accept(listen_fd, (SA *) &cliaddr, &clilen);
|
|   // If SIGTERM arrives ... the following message should be printed!
|   printf("EXIT NOW\n");
|   return 0;
| }
`----

Compiled once on each of the systems:
    $> g++ -D_POSIX_PII_SOCKET -o main main.cc

Execute in 1st shell:
    $> ./main 10000

Execute in 2nd shell:
    $> ps -ef | grep -v grep | grep main
    $> kill -TERM <pid-of-main>

Results (in 1st shell, on OSF):
    EXIT NOW
    $>

Linux exectutes the signal handlers code - but 'accept' does not return. 
So I've no chance to quit my application in case I have to.

Is there any workaround for my problem?


As I did not subscribe to the list; can you please put me on CC personally?

Many thanks and cheers,
Gerrit

Re: accept does not return in case a signal arrives

[Andreas Schwab]

Gerrit Bruchhäuser <gbruchhaeuser@orga-systems.com> writes:

> Given the following sample:
>
> ,----[ main.cc ]
> | #include <sys/types.h>
> | #include <sys/socket.h>
> | #include <errno.h>
> | #include <string.h>
> | #include <stdio.h>
> | #include <stdlib.h>
> | #include <resolv.h>
> | #include <signal.h>
> |
> | #define CHECK_RET_M(arg, x) \
> |   if (-1 == (x) && errno != EINTR) { \
> |      printf("System call '%s' failed: %s\n", #arg, strerror(errno)); \
> |      exit(1); \
> |   }
> |
> | typedef struct sockaddr SA;
> |
> | static void TermHandler(int signu)
> | {
> |    // Nothing
> | }
> |
> | int main(int argc, char *argv[])
> | {
> |   // Create signal handler 4 SIGTERM
> |   signal(SIGTERM, &TermHandler);

Use sigaction.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux AG, Maxfeldstraße 5, 90409 Nürnberg, Germany
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