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

binfmtgcj-interpreter

binfmtgcj(1)							     binfmt_C							      binfmtgcj(1)

NAME

       binfmtgcj-interpreter - binfmt_misc gcj handler

SYNOPSIS

       binfmtgcj-interpreter GCJ-java-source-file-name [command-line opions ...]

DESCRIPTION

       binfmtgcj-interpreter compiles a Java source file specified on the command-line using the GCJ 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 //BINFMTGCJ: at the beginning of the file.

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

ENVIRONMENT

       GCJ    The compiler used.  The default is to use gcj

       BINFMTCTMPDIR

	      Temporary directory used for binary and execution.

	      Falls back to $TMPDIR $TEMPDIR or /tmp

       BINFMTC_DEBUG
	      enables debug output if set.

       BINFMTC_GCJ_OPTS
	      Additional GCJ options.  Use BINFMTC_DEBUG to verify the options being passed on to gcc.

	      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

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

binfmt_misc Dancer						    2005 May 3							      binfmtgcj(1)