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 MINIX

fork

FORK(2) 							System Calls Manual							   FORK(2)

NAME

       fork - create a new process

SYNOPSIS

       #include <sys/types.h>
       #include <unistd.h>

       pid_t fork(void)

DESCRIPTION

       Fork causes creation of a new process.  The new process (child process) is an exact copy of the calling process except for the following:

	      The child process has a unique process ID.

	      The child process has a different parent process ID (i.e., the process ID of the parent process).

	      The  child  process has its own copy of the parent's descriptors.  These descriptors reference the same underlying objects, so that,
	      for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in  the
	      child  process  can affect a subsequent read or write by the parent.  This descriptor copying is also used by the shell to establish
	      standard input and output for newly created processes as well as to set up pipes.

	      The child starts with no pending signals and an inactive alarm timer.

RETURN VALUE

       Upon successful completion, fork returns a value of 0 to the child process and returns the process ID of the child process  to  the  parent
       process.   Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to
       indicate the error.

ERRORS

       Fork will fail and no child process will be created if one or more of the following are true:

       [EAGAIN]       The system-imposed limit on the total number of processes under execution would be exceeded.  This limit	is  configuration-
		      dependent.  (The kernel variable NR_PROCS in <minix/config.h> (Minix), or <minix/const.h> (Minix-vmd).)

       [ENOMEM]       There is insufficient (virtual) memory for the new process.

SEE ALSO

       execve(2), wait(2).

3rd Berkeley Distribution					   May 22, 1986 							   FORK(2)