From c4ed6736d2e093ea7433328a552d53d3bcaff927 Mon Sep 17 00:00:00 2001
From: Ben Burwell <ben@benburwell.com>
Date: Wed, 1 Apr 2015 20:06:27 -0400
Subject: as of 2013-09-30

---
 pcb.c | 189 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 189 insertions(+)
 create mode 100644 pcb.c

(limited to 'pcb.c')

diff --git a/pcb.c b/pcb.c
new file mode 100644
index 0000000..8cffe3f
--- /dev/null
+++ b/pcb.c
@@ -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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