diff options
Diffstat (limited to 'pcb.c')
| -rw-r--r-- | pcb.c | 189 |
1 files changed, 189 insertions, 0 deletions
@@ -0,0 +1,189 @@ +#include "mpx.h"
+#include <string.h>
+#include <stdio.h>
+
+/**
+ * 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 (strcmp(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);
+ 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) {
+ // 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;
+
+ 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;
+ 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;
+
+ // are we removing the head?
+ if (addr == *queue) {
+ *queue = addr->next;
+ (addr->next)->prev = NULL;
+ return 0;
+ }
+
+ // not removing the head:
+ do {
+ if (current->next == addr) {
+ current->next = addr->next;
+ (current->next)->prev = current;
+ addr->next = NULL;
+ addr->prev = NULL;
+ return 0;
+ }
+ current = current->next;
+ } while (current != NULL);
+ return -1;
+}
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