/*ident	"@(#)cls4:lib/task/task/qtail.c	1.3" */
/*******************************************************************************
 
C++ source for the C++ Language System, Release 3.0.  This product
is a new release of the original cfront developed in the computer
science research center of AT&T Bell Laboratories.

Copyright (c) 1993  UNIX System Laboratories, Inc.
Copyright (c) 1991, 1992 AT&T and UNIX System Laboratories, Inc.
Copyright (c) 1984, 1989, 1990 AT&T.  All Rights Reserved.

THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE of AT&T and UNIX System
Laboratories, Inc.  The copyright notice above does not evidence
any actual or intended publication of such source code.

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

/* construct qtail <--> oqueue */
qtail::qtail(qmodetype mode, int max)
{
	if (0 < max) {
		qt_queue = new class oqueue(max);
		qt_queue->q_tail = this;
	};
	qt_mode = mode;
}

/* destroy q if not also pointed to by a qhead */
qtail::~qtail()
{
	oqueue* q = qt_queue;

	if (q->q_head)
		q->q_tail = 0;
	else
		delete q;
}


/* insert object at rear of q (becoming new value of oqueue->q_ptr) */

// q->q_ptr points to last object.  last->o_next points to first object.
// first->o_next points to the next object.
int
qtail::put(object* p)
{
ll:
	register oqueue* q = qt_queue;
	if (p->o_next) task_error(E_PUTOBJ, this);

	if (q->q_count < q->q_max) {
		if (q->q_count++) {
			register object* oo = q->q_ptr;
			p->o_next = oo->o_next;
			q->q_ptr = oo->o_next = p;
		}
		else {	// q was empty; alert those waiting on it
			qhead* h = q->q_head;
			q->q_ptr = p->o_next = p;
			if (h) h->alert();
		}
		return 1;
	}

	switch (qt_mode) {
	case WMODE:
		this_task()->sleep(this);
		goto ll;
	case EMODE:
		task_error(E_PUTFULL, this);
		goto ll;
	case ZMODE:
		return 0;
	}
}


/* create head for this q */
qhead*
qtail::head()
{
	oqueue* q = qt_queue;
	register qhead* h = q->q_head;

	if (h == 0) {
		h = new qhead(qt_mode,0);
		q->q_head = h;
		h->qh_queue = q;
	};

	return h;
}


/* result:  ?qhead<-->? oldq<-->(new)qtail  newq<-->(this)qtail */
qtail*
qtail::cut()
{
	oqueue* oldq = qt_queue;
	qtail* t = new qtail(qt_mode,oldq->q_max);
	oqueue* newq = t->qt_queue;

	t->qt_queue = oldq;
	oldq->q_tail = t;

	newq->q_tail = this;
	qt_queue = newq;

	return t;
}


/* this qtail is supposed to be downstream from the qhead h */
void
qtail::splice(qhead* h)
{
	h->splice(this);
}

void
qtail::print(int n, int baseClass)
{
	if (!baseClass)
		printf("qtail ");

	int m = qt_queue->q_max;
	int c = qt_queue->q_count;
	class qhead * h = qt_queue->q_head;

	printf("mode=%d, max=%d, space=%d, head=%d\n",
		qt_mode, m, m-c, h);

	if (n&VERBOSE) {
		int m = n & ~(CHAIN|VERBOSE);
		if (h) {
			printf("head of queue:\n");
			h->print(m);
		} else printf("\tno head\n");

		qt_queue->print(m);
	}

	object::print(n, 1);
}