added a test for Mutex properties of the locking system

src/main/java/JobServ/ProcessController.java

@@ -124,12 +124,12 @@ class ProcessController {
         try {
             this.input.close();
             this.output.close();
+            this.outputScanner.close();
+            this.process.destroy();
         } catch (IOException e) {
             // streams already closed
         }
 
-        process.destroy();
-
         this.killedManually = true;
     }
 }

src/main/java/JobServ/ProcessManager.java

@@ -225,10 +225,11 @@ class ProcessManager {
     /*
      * getLock()
      * Locks access to this.processQueue
-     * Waits for a predefined timeout period and then grabs the mutex
+     * Waits for a predefined timeout period for mutex to be avail.
+     * Synchronized so two things cannot grab lock at once.
      * Throws TimeoutException when it fails to get the lock.
      */
-    private void getLock() throws TimeoutException {
+    protected synchronized void getLock() throws TimeoutException {
         Future<Object> future = this.threadPool.submit(this.lockCallable);
 
         try {
@@ -266,7 +267,7 @@ class ProcessManager {
      * releaseLock()
      * releases mutex so other threads can operate on processqueue
      */
-    private void releaseLock() {
+    protected void releaseLock() {
         this.processQueueMutex = false;
     }
 

src/test/java/JobServ/ProcessManagerTest.java

@@ -15,6 +15,10 @@ import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
 
+import java.util.concurrent.Future;
+import java.util.concurrent.Callable;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ExecutorService;
 
 /*
  * ProcessManagerTest
@@ -24,15 +28,16 @@ import static org.junit.Assert.assertNotEquals;
  * tests it with ProcessController.
  */
 public class ProcessManagerTest {
-    ProcessManager manager;
+    private ProcessManagerTestImplementation manager = new ProcessManagerTestImplementation();
+    private ExecutorService threadPool = Executors.newCachedThreadPool();
 
-    /*
-     * ProcessManagerTest constructor
-     * initializes the process manager
-     */
-    public ProcessManagerTest() {
-        manager = new ProcessManager();
+    // calls a test function that simulates load by holding the lock for a long time
+    private Callable<Object> holdLockSevenSeconds = new Callable<Object>() {
+            public Object call() {
+                manager.longCallHoldsLock();
+                return true;
             }
+        };
 
     /*
      * addProcessTest()
@@ -175,5 +180,31 @@ public class ProcessManagerTest {
 
         manager.shutdown();
     }
+
+    /*
+     * asyncLockTimeoutTest
+     * ensures that two things cannot grab the lock at the same time
+     */
+    @Test
+    public void asyncLockTimeoutTest() {
+        Future<Object> future = this.threadPool.submit(this.holdLockSevenSeconds);
+
+        try {
+            Thread.sleep(50);
+        } catch (InterruptedException e) {
+            System.err.println("[!!] Thread for async test interrupted!");
+        }
+
+        System.err.println("[2] attempting to grab (held) lock");
+        int pid = this.manager.newProcess("Test Process");
+        assertEquals(-1, pid);
+
+        future.cancel(true);
+
+        int pid2 = this.manager.newProcess("echo test");
+        assertNotEquals(-1, pid2);
+
+        manager.shutdown();
+    }
 }
 

src/test/java/JobServ/ProcessManagerTestImplementation.java

@@ -0,0 +1,41 @@
+/*
+ * ProcessManagerTestImplementation
+ *
+ * v1.0
+ *
+ * May 23, 2019
+ */
+
+
+package JobServ;
+
+import java.util.concurrent.TimeoutException;
+
+/*
+ * ProcessManagerTestImplementation
+ * inherits ProcessManager and adds useful functions for testing
+ */
+class ProcessManagerTestImplementation extends ProcessManager {
+
+    public void longCallHoldsLock() {
+        try {
+            super.getLock();
+            System.err.println("[1] Long Call Has Lock");
+
+            // hold lock for 7 seconds, more than double normal timeout.
+            Thread.sleep(4000);
+
+            super.releaseLock();
+
+        } catch (TimeoutException e) {
+            System.err.println("[!!] Long Call wasnt able to grab lock!");
+            return;
+
+        } catch (InterruptedException e) {
+            super.releaseLock();
+            System.err.println("[3] Released lock: interrupted");
+            return;
+        }
+    }
+
+}