cmtports.c

简单实现多任务的C语言库 可以实现各个任务间的简单的消息通讯

#include "cmtlib.h"

/* ----------------------------------------------------------------
** Ports.
** ----------------------------------------------------------------
*/
/*man**************************************************************
NAME
	cmt_pcreate - create a message port

SYNOPSIS
	#include "cmtlib.h"

	CMT_PORT far * far cdecl cmt_pcreate(int size)

DESCRIPTION
	this function creates a message port for a given number
	of messages. in our multitasker, messages are always
	void far pointers, the given size indicates how many pointers
	this port can hold.

DIAGNOSTICS
	returns pointer to newly created port or NULL
******************************************************************/
CMT_PORT far * far cdecl cmt_pcreate(int size)
{
int i;
CMT_PORT far *np=NULL;
	if (size>0) {
		np=cmt_malloc(sizeof(CMT_PORT)+size*sizeof(void far *));
		if (np) {
			for (i=0;i<size;i++)
				np->port[i]=NULL;
			np->size=size;
			np->nmsgs=np->head=np->tail=0;
		}		
	}
	return np;
}

/*man**************************************************************
NAME
	cmt_pdelete - discards a message port

SYNOPSIS
	#include "cmtlib.h"

	CMT_PORT far * far cdecl cmt_pdelete(CMT_PORT far *port)

DESCRIPTION
	this function discards a message port.

DIAGNOSTICS
	always returns NULL

NOTES
	this function does not check if the port has any
	pending messages (which would be lost after the port
	is discarded).
******************************************************************/
CMT_PORT far * far cdecl cmt_pdelete(CMT_PORT far *port)
{
	if (port)
		cmt_free(port);
	return NULL;
}

/*man**************************************************************
NAME
	cmt_psend - sends a message to port

SYNOPSIS
	#include "cmtlib.h"

	void far cdecl cmt_psend(CMT_PORT far *port,void far *message)

DESCRIPTION
	send a message to message port. if the port is full, this
	function blocks until there is room for another message.
******************************************************************/
void far cdecl cmt_psend(CMT_PORT far *port,void far *message)
{
	if (port) {
		while (port->nmsgs>=port->size)
			cmt_pause();
		port->port[port->head++]=message;
		if (port->head>=port->size)
			port->head=0;
		port->nmsgs++;
	}
}

/*man**************************************************************
NAME
	cmt_psendnobl - sends a message to port, not blocking

SYNOPSIS
	#include "cmtlib.h"

	int far cdecl cmt_psendnobl(CMT_PORT far *port,void far *message)

DESCRIPTION
	tries to send a message to message port

DIAGNOSTICS
	returns 1 if the message is successfully delivered or 0 if the
	port is full
******************************************************************/
int far cdecl cmt_psendnobl(CMT_PORT far *port,void far *message)
{
	if (port) {
		if (port->nmsgs>=port->size)
			return 0;
		port->port[port->head++]=message;
		if (port->head>=port->size)
			port->head=0;
		port->nmsgs++;
		return 1;
	}
	return 0;
}

/*man**************************************************************
NAME
	cmt_preceive - receive a message from port

SYNOPSIS
	#include "cmtlib.h"

	void far * far cdecl cmt_preceive(CMT_PORT far *port)

DESCRIPTION
	receives a message from a port. blocks until a message
	becomes avaiable

DIAGNOSTICS
	returns a message
******************************************************************/
void far * far cdecl cmt_preceive(CMT_PORT far *port)
{
void *m=NULL;
	if (port) {
		while (!port->nmsgs)
			cmt_pause();
		m=port->port[port->tail++];
		if (port->tail>=port->size)
			port->tail=0;
		port->nmsgs--;
	}
	return m;
}

/*man**************************************************************
NAME
	cmt_pcount - returns number of messages in the port

SYNOPSIS
	#include "cmtlib.h"

	int far cdecl cmt_pcount(CMT_PORT far *port)

DESCRIPTION
	this function simply returns a number of messages
	that are waiting delivery in the port.

DIAGNOSTICS
	returns number of pending messages
******************************************************************/
int far cdecl cmt_pcount(CMT_PORT far *port)
{
	return port->nmsgs;
}