Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!ncrlnk!ncrcae!hubcap!wen-king
From: wen-king@csvax.caltech.edu (Wen-King Su)
Newsgroups: comp.parallel
Subject: Re:  using network machines as compute servers
Message-ID: <7300@hubcap.clemson.edu>
Date: 4 Dec 89 14:08:01 GMT
Sender: fpst@hubcap.clemson.edu
Lines: 90
Approved: parallel@hubcap.clemson.edu

>From: larsa@nada.kth.se (Lars Andersson)

I recommend Cosmic Environment because:

    1) Cosmic Environment runs without modification on all implementations
       of BSD, System V, and Xenix OS with socket support.  

    2) CE's message model is simple and intuitive -- just like malloc and free.

    3) CE message primitives are general and satisfies most programming needs.

    4) CE message primitives can be simply and efficiently emulated in almost
       all multicomputer programming systems.  Therefore, porting CE programs
       to other systems is quite simple.  This is a way to protect your
       investiment in your programs.

<Consider the following: One "master" puts  "tasks" in a batch, there to be
>picked up by the "slaves" as each completes its current task. When a slave
<completes a task it puts the solution in an appropriate batch, there to be
>picked up and stored by the master (depending on the problem, one might want
<to write directly to a file ...). 

This can't be that difficult.  You write a batch process (listed below).
The master put tasks into the batch by sending 'ADD' messages to the batch
process.  The slave process gets a task by sending a 'GET' message to the
batch process and waiting for a 'ADD' message in reply.  You can use another
batch process to collect the results, or add more message types to this
batch program to handle collection of results.

The 'body' of 'ADD' messages contains task specification.  In the simplest
case, it can be a string to be passed to shell.  And the slave process
simply do a "system(message->body)" when it gets the 'ADD' message it asked for.

----------------------------------------------------------------------------
#include <cube/cubedef.h>

typedef struct MHEAD MHEAD;

struct MHEAD {	MHEAD *next;		/* for making a queue */
		short type;		/* type of the message */
		short node, pid;	/* reference of the sender process */
		short count;		/* number of bytes in message body */
		char  body[1]; };	/* actually 'count' bytes long */

MHEAD *task_head, *task_tail;	/* queues of tasks to be work on */
MHEAD *wait_head, *wait_tail;	/* queues of processes waiting for work */

#define ADD 1
#define GET 2

main()
{
    MHEAD *mp, *tp, *wp;

    while(mp = (MHEAD *) xrecvb())	/* repeatedly get a message */
    {
	if(mp->type == ADD)		/* message to add a task.  */
	{
	    if(!wait_head)		/* task not waited for -> queue it */
	    {
		if(task_head) task_tail = task_tail->next = tp;
			 else task_tail = task_head       = tp;
		tp->next = 0;

	    } else			/* waited for -> dispatch task */
	    {
		wp = wait_head; wait_head = wp->next;
		xsend(mp,wp->node,wp->pid); xfree(wp);
	    }

	} else

	if(mp->type == GET)		/* message to get a task */
	{
	    if(!task_head)		/* no task available -> queue it */
	    {
		if(wait_head) wait_tail = wait_tail->next = wp;
			 else wait_tail = wait_head       = wp;
		wp->next = 0;

	    } else			/* available -> dispatch task */
	    {
		tp = task_head; task_head = tp->next;
		xsend(tp,mp->node,mp->pid); xfree(mp);
	    }
	}
    }
}

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