Parent,child wait,signal Post: 302528245

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Top Forums Programming Parent,child wait,signal Post 302528245 by Corona688 on Monday 6th of June 2011 05:47:18 PM

06-06-2011

Registered User

Quote:

Originally Posted by Cuervo

Corona688 i think you mistook FIFO with pipes...right?

Nope. Look at what I said more closely. I never said anything about writing to the fifo, but what happens when you open it.

Lemme write you a little example.

Code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(void)
{
        pid_t pid;
        int fd;
        mkfifo("./myfifo", 0660);

        pid=fork();
        if(pid == 0)    // child code
        {
                fprintf(stderr, "C\tWaiting 3 seconds\n");
                sleep(3);
                fprintf(stderr, "C\tOpening fifo\n");
                fd=open("./myfifo", O_RDONLY);
                fprintf(stderr, "C\tOpening fifo\n");
                fd=open("./myfifo", O_RDONLY);
                exit(0);
        }
        else if(pid > 0)        // parent code
        {
                fprintf(stderr, "P\tOpening fifo\n");
                fd=open("./myfifo", O_WRONLY);
                fprintf(stderr, "P\tFIFO opened\n");
                exit(0);
        }

        perror("Couldn't fork");
        return(1);
}

The parent creates the fifo, then creates the child, then tries to immediately open the fifo.

The child waits 3 seconds before opening the fifo, forcing the parent to wait 3 seconds as well. The fifo will finish opening only when there's something trying to open both ends.

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LEARN ABOUT CENTOS

xmobjectatpoint

XmObjectAtPoint(library call)											     XmObjectAtPoint(library call)

NAME

       XmObjectAtPoint -- A toolkit function that determines which child intersects or comes closest to a specified point

SYNOPSIS

       #include <Xm/Xm.h>
       Widget XmObjectAtPoint(
       Widget widget,
       Position x,
       Position y);

DESCRIPTION

       XmObjectAtPoint	searches  the  child list of the specified manager widget and returns the child most closely associated with the specified
       x,y coordinate pair.

       For the typical Motif manager widget, XmObjectAtPoint uses the following rules to determine the returned object:

	  o  If one child intersects x,y, XmObjectAtPoint returns the widget ID of that child.

	  o  If more than one child intersects x,y, XmObjectAtPoint returns the widget ID of the visible child.

	  o  If no child intersects x,y, XmObjectAtPoint returns NULL.

       The preceding rules are only general. In fact, each manager widget is free to define "most closely associated" as it desires.  For example,
       if no child intersects x,y, a manager might return the child closest to x,y.

       widget	 Specifies a manager widget.

       x	 Specifies  the x-coordinate about which you are seeking child information. The x-coordinate must be specified in pixels, relative
		 to the left side of manager.

       y	 Specifies the y-coordinate about which you are seeking child information. The y-coordinate must be specified in pixels,  relative
		 to the top side of manager.

RETURN

       Returns the child of manager most closely associated with x,y.  If none of its children are sufficiently associated with x,y, returns NULL.

RELATED

       XmManager(3).

														     XmObjectAtPoint(library call)

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