Q58779: After Increasing Available File Handles, exec Hangs Machine

Article: Q58779
Product(s): See article
Version(s): 5.00 5.10 6.00 6.00a
Operating System(s): MS-DOS
Keyword(s): ENDUSER | buglist5.00 buglist5.10 buglist6.00 buglist6.00a | mspl13_c
Last Modified: 14-JAN-1991

If you have increased the maximum number of file handles and buffers
available to the system by changing the _file.c and crt0dat.asm
start-up source files as outlined in the README.DOC file, and then
write a program that does multiple execs, your machine may hang under
DOS.

There is a known incompatibility between changing the start-up source
code for the optimizing C compilers and exec'ing multiple child
processes.

The following sample code demonstrates this problem:

#define FILES_OPEN 30

#include <stdio.h>
#include <conio.h>
#include <process.h>
#include <errno.h>
#include <string.h>

void main ( void )
{
    short numfiles, returnval;
    FILE *FilePointer;
    char fname[80];

    for ( numfiles = 0; numfiles < FILES_OPEN; numfiles ++ )
    {
        sprintf ( fname, "file%2d.dat", numfiles ) ;
        printf ( "Opening file #%2d :%s\n", numfiles, fname ) ;

        if ( ( FilePointer = fopen ( fname, "a+" ) ) == NULL )
        {
            printf ( "fopen failed on file #%2d", numfiles ) ;
            exit ( -2 ) ;
        }
    }

    printf ( " Press <esc> to quit, other to continue exec'ing child: \n" ) ;

    if ( ( returnval = getche() ) == 27 )
    {
        printf ( "Quitting...\n" ) ;
        exit ( 1 ) ;
    }

    if ( ( returnval = execlp ( "child.exe", "child.exe", NULL )) == -1 )
    {
        printf ( "Error exec'ing child; ERRNO: %d\n", errno ) ;
    }
}

If you make a copy of this program and call it child.c, and change all
references in the child.c program from child to parent, you will have
a loop of exec's set up. You can exec the child once, then your
machine either hangs on the call to exec the first program again or as
the second program is finishing execution.

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