When I am writing my own interpreter... Post: 302142009

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Top Forums Programming When I am writing my own interpreter... Post 302142009 by Legend986 on Wednesday 24th of October 2007 12:57:38 AM

10-24-2007

Registered User

Thanks to everyone here... I am slowly able to realize the shell... I'm actually stuck at piping... I am able to handle a single pipe but how do I solve the problem of multiple pipes? I know it can be solved using recursion but some pseudo algorithm will be excellent... I don't understand how to actually use recursion here... I'm currently doing something like a parent creates two children and the first one executes one command and pipes it onto the second child which displays the output...

And when I used valgrind, to my surprise I found 15 memory leaks from the piping function that I wrote and I don't understand what could've gone wrong... My pseudo code looks something like this:

Code:

	
	int fd[2]; /* provide file descriptor pointer array for pipe */
	pid_t pid1, pid2; /* process ids for each child */
	/* create pipe and check for an error */
	/* apply fork and check for error */
	    /* processing for child */
	    close (fd[1]); /* close output end, leaving input open */
	    /* set standard input to pipe */
	    if (fd[0] != STDIN_FILENO)
	    {
		if (dup2(fd[0], STDIN_FILENO) != STDIN_FILENO)
		{
		    perror("dup2 error for standard input");
		    exit(1);
		}
		close(fd[0]);
	    }
	   execlp the second function
	    //First child finished
	
	else
	{
	    /* processing for parent */
	    /* spawn second process */
	   /* apply fork again for second child*/
	  /* processing for child */
		
		close (fd[0]);
		/* set standard output to pipe */
		if (fd[1] != STDOUT_FILENO)
		{
		    if (dup2(fd[1], STDOUT_FILENO) != STDOUT_FILENO)
		    {
			perror("dup2 error for standard output");
			exit(1);
		    }
		    close(fd[1]); /* not needed after dup2 */
		}
		
		execlp the first function
		/* print to the pipe, now standard output */
	    }
	    else
	    {
		/* processing continues for parent */
		close(fd[0]);
		close(fd[1]);
		waitpid (pid1, NULL, 0); /* wait for first child to finish */
		waitpid (pid2, NULL, 0); /* wait for second child to finish */
	   }
	}

Am I doing something wrong?

Last edited by Legend986; 10-24-2007 at 02:45 AM..

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LEARN ABOUT DEBIAN

binfmtasm-interpreter

binfmtasm(1)							     binfmt_C							      binfmtasm(1)

NAME

       binfmtasm-interpreter - binfmt_misc Assembly handler

SYNOPSIS

       binfmtasm-interpreter Assembly-source-file-name [command-line opions ...]

DESCRIPTION

       binfmtasm-interpreter compiles an assembly source file specified on the command-line using gas compiler, and executes the resulting file.

       It  is  designed  to be used as a handler for binfmt_misc handler, which is a system used in Linux for handling arbitrary files as executa-
       bles.

       The command-line options are passed on to the compiled binary.

FILE MAGIC

       There is a requirement for C++ source files to have the magic characters /*BINFMTASMCPP: at the beginning of the file.

       That line also is used to specify the additional command-line options for the assmebler.

ENVIRONMENT

       GAS    The compiler used.  The default is to use gcc

       AS     The compiler used, if GAS variable is not set.

	      Will fall back to using GCC and CC

       BINFMTCTMPDIR

	      Temporary directory used for binary and execution.

	      Falls back to $TMPDIR $TEMPDIR or /tmp

       BINFMTC_DEBUG
	      enables debug output if set.

       BINFMTASM_GAS_OPTS
	      Additional G++ options.  Use BINFMTC_DEBUG to verify the options being passed on to g++.

	      The default is  -O2 -Wall

AUTHOR

       Junichi Uekawa (dancer@debian.org)

       Upstream page is available at http://www.netfort.gr.jp/~dancer/software/

SEE ALSO

       binfmtc-interpreter(1), binfmtcxx-interpreter(1), binfmtf-interpreter(1), binfmtf95-interpreter(1), binfmtgcj-interpreter(1)

binfmt_misc Dancer						    2005 May 3							      binfmtasm(1)