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#include "mpx.h"
#include <string.h>
#include <stdio.h>
#include <dos.h>
#define STK_PSW (STACK_SIZE - 1)
#define STK_CS (STACK_SIZE - 2)
#define STK_IP (STACK_SIZE - 3)
#define STK_DS (STACK_SIZE - 9)
#define INIT_STACK (STACK_SIZE - 12)
/**
* Returns the address of the PCB with the specified name
*/
pcb * search_pcb(pcb * list, char name[]) {
pcb * current = list;
// step through the chain
do {
if (stricmp(current->name, name) == 0) {
return current;
}
current = current->chain;
} while (current != NULL);
// nothing found
return NULL;
}
/**
* Returns the address of the first free PCB.
* If all PCBs are in use, it returns NULL.
*/
pcb * get_pcb(pcb * list) {
pcb * current = list;
// step through the list
do {
if (current->type == FREE) {
return current;
}
current = current->chain;
} while (current != NULL);
// no free PCBs
return NULL;
}
/**
* Sets the specified PCB to be free.
*/
int free_pcb(pcb * list, pcb * addr) {
pcb * current = list;
do {
if (current == addr) {
// check if PCB is already free
if (current->type == FREE) {
// it is, so we don't free it
return -2;
} else {
// we need to free the PCB
build_pcb(current, " ", 0, -1, -1, 0, NULL, NULL, NULL, NULL);
return 1;
}
}
current = current->chain;
} while (current != NULL);
// invalid PCB address
return -1;
}
/**
* Sets the properties of the given PCB.
*/
int build_pcb(pcb * addr, char name[], int type, int state,
int suspend, int priority, unsigned cs, unsigned ip,
unsigned ds, unsigned psw) {
// check that address is valid
if (addr == 0 || addr == NULL) {
return -1;
}
// check that type is FREE, SYS_PROCESS, APP_PROCESS
if (type != FREE && type != SYS_PROCESS && type != APP_PROCESS) {
return -2;
}
// check that state is READY, RUNNING, BLOCKED, or -1 for free
if (state != READY && state != RUNNING &&
state != BLOCKED && state != -1) {
return -3;
}
// check that suspend is SUSPENDED, NOT_SUSPENDED or -1 for free
if (suspend != SUSPENDED && suspend != NOT_SUSPENDED && suspend != -1) {
return -4;
}
strcpy(addr->name, name);
addr->type = type;
addr->state = state;
addr->suspend = suspend;
addr->next = NULL;
addr->prev = NULL;
addr->priority = priority;
// set up the stack
addr->stack[STK_PSW] = psw;
addr->stack[STK_CS] = cs;
addr->stack[STK_IP] = ip;
addr->stack[STK_DS] = ds;
addr->stack_ptr =(unsigned) &(addr->stack[INIT_STACK]);
addr->loadaddr = cs;
return 1;
}
/**
* Puts the specified PCB into the specified queue, using either
* FIFO or priority queue (method==0: priority, method==1: FIFO)
*/
int insert_pcb(pcb **queue, pcb * addr, int method) {
pcb * current = *queue;
pcb * one_after;
// if there's nothing in the queue yet, make the PCB the start
if (current == NULL) {
*queue = addr;
return 1;
}
if (method == 1) {
// insert at end of queue
// skip to the end of the queue
while(current->next != NULL) {
current = current->next;
}
// add the PCB
current->next = addr;
addr->next = NULL;
addr->prev = current;
return 1;
} else if (method == 0) {
// insert in priority order
// if we need to skip forward at all...
if (current->priority >= addr->priority) {
// ...do it
while (current->next != NULL &&
(current->next)->priority >= addr->priority) {
current = current->next;
}
// and set the pointers
one_after = current->next;
current->next = addr;
addr->next = one_after;
addr->prev = current;
if (one_after != NULL) {
one_after->prev = addr;
}
} else {
// otherwise, put it at the head
current->prev = addr;
addr->next = current;
*queue = addr;
}
return 1;
} else {
// There was a problem, return error code
return -1;
}
}
/**
* Takes the PCB out of the specified queue
*/
int remove_pcb(pcb **queue, pcb * addr) {
pcb * current = *queue;
if (addr == NULL || *queue == NULL) {
printf("bad times ahead \n");
return;
}
// are we removing the head?
if (addr == *queue) {
*queue = addr->next;
if (addr->next != NULL) {
(addr->next)->prev = NULL;
addr->next = NULL;
}
return 0;
}
// not removing the head:
do {
if (current->next == addr) {
current->next = addr->next;
if (current->next != NULL) {
(current->next)->prev = current;
}
addr->next = NULL;
addr->prev = NULL;
return 0;
}
current = current->next;
} while (current != NULL);
return -1;
}
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