When I am writing my own interpreter... Post: 302142329

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Top Forums Programming When I am writing my own interpreter... Post 302142329 by matrixmadhan on Thursday 25th of October 2007 01:51:14 PM

10-25-2007

Registered User

Quote:

Originally Posted by Legend986

I was actually thiniking about one silly thing: when I'm creating multiple pipes, I need to create multiple file descriptors right? How would I do that? Just define a pool of unused file descriptors and use them only when I need them or is there any other way?

I tried defining using
int fd[4][2];

to get four pipes but it isn't working due to some obvious reason I guess... Any advice please?

This is a great attempt ! Smilie

If the file descriptors data type is defined as
int fd[4][2]; again you are imposing the limit on the number of processes that could be piped to each other.

( Or is that you are trying first with 'n' number of processes for piping where n <= 4 and then moving on to a more generic attempt )

##############

When replying to this thread I got this doubt, may be worth asking this along with this thread.

So basically pipe is a KDS - kernel data structure with its own memory capacity, therefore number of bytes that it can hold.

Take an example piping process like this

Code:

ls | wc -l

( assume ls runs over a million files and definitely has to take some 'n' number of seconds to complete that )

case 1 : Should wc process need to wait till lc flushes all the filenames to the ' | ' ?
case 2: Or as and when ' ls ' lists the filenames to the kernel data structure ' wc ' process would start using that information to count on the number of files.

What would be scenario if the information from process 1 ' ls ' overruns the capacity of the pipe data structure? Will the process 1 be signalled by the kernel to stop flushing data to pipe and at the same time process 2 signalled by the kernel to start using the data from the KDS so that process 1 can push in more information to the pipe data structure.

Is this how pumping information in to the pipe by process 1 and using the information by process 2 happens ?

Keep this thread alive, it is becoming more interesting Smilie

matrixmadhan

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LEARN ABOUT FREEBSD

atf-sh

ATF-SH(1)						    BSD General Commands Manual 						 ATF-SH(1)

NAME

     atf-sh [-s shell] -- interpreter for shell-based test programs

SYNOPSIS

     atf-sh script

DESCRIPTION

     atf-sh is an interpreter that runs the test program given in script after loading the atf-sh(3) library.

     atf-sh is not a real interpreter though: it is just a wrapper around the system-wide shell defined by ATF_SHELL.  atf-sh executes the inter-
     preter, loads the atf-sh(3) library and then runs the script.  You must consider atf-sh to be a POSIX shell by default and thus should not
     use any non-standard extensions.

     The following options are available:

     -s shell	  Specifies the shell to use instead of the value provided by ATF_SHELL.

ENVIRONMENT

     ATF_LIBEXECDIR    Overrides the builtin directory where atf-sh is located.  Should not be overridden other than for testing purposes.
     ATF_PKGDATADIR    Overrides the builtin directory where libatf-sh.subr is located.  Should not be overridden other than for testing purposes.
     ATF_SHELL	       Path to the system shell to be used in the generated scripts.  Scripts must not rely on this variable being set to select a
		       specific interpreter.

EXAMPLES

     Scripts using atf-sh(3) should start with:

	   #! /usr/bin/env atf-sh

     Alternatively, if you want to explicitly choose a shell interpreter, you cannot rely on env(1) to find atf-sh.  Instead, you have to hardcode
     the path to atf-sh in the script and then use the -s option afterwards as a single parameter:

	   #! /path/to/bin/atf-sh -s/bin/bash

ENVIRONMENT

     ATF_SHELL	  Path to the system shell to be used in the generated scripts.

SEE ALSO

     atf-sh(3)

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