Added Process exercise's chapter

pid_manager.c

@@ -0,0 +1,63 @@
+#include "pid_manager.h"
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MIN_PID 300
+#define MAX_PID 5000
+#define SIZE (MAX_PID - MIN_PID + 1)
+
+bool pids[SIZE];
+
+int allocate_map(void) {
+  for (int i = 0; i < SIZE; i++) {
+    pids[i] = false;
+  }
+  return 1;
+}
+
+int allocate_pid(void) {
+  for (int i = 0; i < SIZE; i++) {
+    if (!pids[i]) {
+      pids[i] = true;
+      return i + MIN_PID;
+    }
+  }
+  return -1;
+}
+
+void release_pid(int pid) {
+  if (pid >= MIN_PID && pid <= MAX_PID) {
+    pids[pid - MIN_PID] = false;
+  }
+}
+
+int main(void) {
+  if (allocate_map() != 1) {
+    perror("Failed to initialiaze PID Manager\n");
+    exit(1);
+  }
+
+  for (int i = 0; i < SIZE; i++) {
+    printf("Allocate PID = %d\n", allocate_pid());
+  }
+
+  int last = allocate_pid();
+  printf("Attempt to allocate another PID, result %d\n", last);
+
+  if (last == -1) {
+    printf("Release a PID 4000\n");
+    release_pid(4000);
+  }
+
+  printf("Allocate another PID: %d\n", allocate_pid());
+
+  printf("Release PIDs 300 and 5000\n");
+  release_pid(300);
+  release_pid(5000);
+
+  printf("Allocate another PID: %d\n", allocate_pid());
+  printf("Allocate another PID: %d\n", allocate_pid());
+
+  return 0;
+}