Pro*C Infinite loop at WIFEXITED

Reima Cram · 09-18-2013, 12:04 AM

Hello,

This might be noobish but here it goes.

Problem:
In a pro*C program we have it somehow do an infinite loop on the following piece of code.

Code:

int exec_cmd(cmd)
    char      *cmd;
{
    int         nPid;
    int         nStatus;
    char       *argv[10];
    int         argc = 0;

    nPid = fork();
    if (nPid > 0) {
        waitpid(nPid, &nStatus, 0);
/*problem in the while below*/
        while ( WIFEXITED(nStatus) == 0 )  
            waitpid(nPid, &nStatus, 0);
        return ((WEXITSTATUS(nStatus) > 0) ? 1 : 0);   
    } 
    else if (nPid == 0) {
        nPid = getpid();
        argv[argc++] = "/bin/sh";
        argv[argc++] = "-c";
        argv[argc++] = cmd;
        argv[argc++] = NULL;
        /*sigignore(SIGCHLD);*/
        if (execv(argv[0],argv) < 0) {
            printf("error\n");
            return 0;
        }
        return 1; 
    }
}

Initial Check:
The code above is part of a Proc*C program that basically uses sqlldr to load interface files to DB.
We were using SuSe 9 before on one server and it works just fine. This test server has Suse 11 Sp2. Upon compilation and other related configs like dos2unix was done, it somehow stops on this piece of command.
Can you guys give me an idea if internal functions like fork(), etc was changed or something? I'm really sorry that I ask this type of question. Any ideas would be appreciated.

dwhitney67 · 09-18-2013, 06:42 PM

I don't anything about Pro*C, but if the execv() call is similar to that in the Unix/Linux "standard" library, then if the call is successful, then calling program will never return. Thus your forked child process will never hit the "return 1" statement.

Sorry, I hit the 'save' button to quickly... I wanted to add that otherwise, your program seems fine. Perhaps you could diagnose the problem you are witnessing with debug statements or even using the debugger.

ntubski · 09-18-2013, 09:29 PM

Code:

        waitpid(nPid, &nStatus, 0);
/*problem in the while below*/
        while ( WIFEXITED(nStatus) == 0 )  
            waitpid(nPid, &nStatus, 0);
        return ((WEXITSTATUS(nStatus) > 0) ? 1 : 0);

It makes no sense to me to call waitpid() in a loop: waitpid() will only return after the child process is finished, there is no use calling it again. If you're getting stuck in the loop, that indicates the child process didn't exit cleanly. I think you want something like this:

Code:

waitpid(nPid, &nStatus, 0);
if (WIFEXITED(nStatus)) {
    return WEXITSTATUS(nStatus);
} else if (WIFSIGNALED(nStatus)) {
    fprintf(stderr, "child died by signal: %d\n", WTERMSIG(nStatus));
#   ifdef WCOREDUMP
        if (WCOREDUMP(nStatus))
           fprintf(stderr, "core dumped\n");
#   endif
    return 128;
} else {
    fprintf(stderr, "this should never happen...\n");
    return 255;
}

Reima Cram · 09-19-2013, 06:35 AM

thanks for your replies. will apply it to my code and try your suggestions. I will get back to you as soon as i can.

Cheers!

NevemTeve · 09-19-2013, 10:13 AM

Note: I may be blind, but cannot see where any Oracle-precompiler related part is in this code.