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shared.C

by Michael L Powell last modified 2007-01-26 03:22

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/*ident	"@(#)ctrans:demo/task/shared.C	1.1" */
/**************************************************************************
			Copyright (c) 1984 AT&T
	  		  All Rights Reserved  	

	THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF AT&T
	
	The copyright notice above does not evidence any   	
	actual or intended publication of such source code.

*****************************************************************************/
#include <task.h>

/*
 * shared.C
 * Modified example from "Appendix:  A Program Using Tasks" section of
 * Stroustrup/Shopiro coroutine memo, Release Notes pp 13-23 - 13-24.
 * non-trivial test example:
 *	Makes a set of SHARED tasks which pass an object around.
 *	Each task but the last creates the next task.
 *	Each task gets an object from the head of one queue, and puts
 *	the object on the tail of another queue.
 *	Each task quits after getting the object MAX_CYCLES times.
 */

const int NTASKS = 1;
const int MAX_CYCLES = 5;

struct pc : task {				// derive a class from task
        pc(char*, qtail*, qhead*);		// task is not intended to
};						// be used directly

pc::pc(char* n, qtail* t, qhead* h) : task(n, SHARED) // task body serves as
{						// "main" program for task
	int cycles;

        printf("new pc(%s)\n",n);
	if (*n < 'a'+ NTASKS) {
		char*	c = new char[2]; c[0] = *n + 1; c[1] = '\0';
		qtail*	qt = new qtail;
		pc*	next = new pc(c, t, qt->head());
		t = qt;
	} else {
		printf("%s: here we go\n", n);
		t->put(new object);
	}
        for (cycles = 0; cycles < MAX_CYCLES; cycles++) {
		object* p = h->get();
		printf("task %s\n",n);
		t->put(p);
	}
	printf("task %s: done.\n", n);
	resultis(0);		// Always end task constructors with resultis.
				// Behavior of those using return or running
				// off the end of the function is undefined.
				// Alternatively, use an infinite loop in
				// constructor body.
}

main()
{
	qhead* hh = new qhead;
	qtail* t = hh->tail();
	qhead* h;
	int cycles;

	printf("main\n");

	char* n = "a"; // make a one letter task name

	h = new qhead;
	new pc(n,t,h);
	printf("main()'s loop\n");
	t = h->tail();
        for (cycles = 0; cycles < MAX_CYCLES; cycles++) {
		object* p = hh->get();
		printf("main task\n");
		t->put(p);
	}
	printf("main task: done.\n", n);
	thistask->resultis(0);		// main is a task too; it must also
					// end with resultis (to allow any
					// remaining tasks to run, otherwise
					// the whole process would exit).
}

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