Corrected false assumption in caching logic.

src/main/java/ca/recrown/islandsurvivalcraft/caching/Cache.java

@@ -57,15 +57,16 @@ public class Cache<K, V> {
      * @return the value associated to the key.
      */
     public V get(K key) {
-        readLock.lock();
         CacheValue<K, V> value = null;
-        try {
-            if (!data.containsKey(key)) return null;
         value = data.get(key);
+        if (value == null) return null;
+        if (readLock.tryLock()) {
+            try {
                 usage.tryMoveToTop(value);
             } finally {
                 readLock.unlock();
             }
+        }
         return value.value;
     }
 

src/main/java/ca/recrown/islandsurvivalcraft/caching/CacheUsageStack.java

@@ -7,27 +7,28 @@ class CacheUsageStack<K, V> {
     private volatile CacheValue<K, V> first, last;
     private final ReentrantLock lock = new ReentrantLock();
 
-    private void addToTop(CacheValue<K, V> value) {
+    private void addValueToStackTop(CacheValue<K, V> value) {
         if (first != null) {
             first.front = value;
             value.back = first;
         } else {
             last = value;
         }
+
         value.front = null;
         first = value;
         size++;
     }
 
-    private void removeValue(CacheValue<K, V> value) {
+    private void removeValueFromStack(CacheValue<K, V> value) {
         if (value.front != null) {
             value.front.back = value.back;
-        } else {
+        } else if (first == value) {
             first = value.back;
         }
         if (value.back != null) {
             value.back.front = value.front;
-        } else {
+        } else if (last == value) {
             last = value.front;
         }
         value.front = null;
@@ -38,8 +39,10 @@ class CacheUsageStack<K, V> {
     public void moveToTop(CacheValue<K, V> value) {
         lock.lock();
         try {
-            removeValue(value);
-            addToTop(value);
+            if (!value.detached) {
+                removeValueFromStack(value);
+                addValueToStackTop(value);
+            }
         } finally {
             lock.unlock();
         }
@@ -50,8 +53,7 @@ class CacheUsageStack<K, V> {
         success = lock.tryLock();
         if (success) {
             try {
-                removeValue(value);
-                addToTop(value);
+                moveToTop(value);
             } finally {
                 lock.unlock();
             }
@@ -62,7 +64,7 @@ class CacheUsageStack<K, V> {
     public void add(CacheValue<K, V> value) {
         lock.lock();
         try {
-            addToTop(value);
+            addValueToStackTop(value);
         } finally {
             lock.unlock();
         }
@@ -73,7 +75,8 @@ class CacheUsageStack<K, V> {
         lock.lock();
         try {
             cacheValue = last;
-            removeValue(last);
+            removeValueFromStack(last);
+            cacheValue.detached = true;
         } finally {
             lock.unlock();
         }

src/main/java/ca/recrown/islandsurvivalcraft/caching/CacheValue.java

@@ -1,7 +1,23 @@
 package ca.recrown.islandsurvivalcraft.caching;
 
 class CacheValue<KeyType, ValueType> {
+    /**
+     * The key that represents this cache value in the caches hashmap.
+     */
     public volatile KeyType key;
+
+    /**
+     * The actual value that this cache value stores.
+     */
     public volatile ValueType value;
+
+    /**
+     * The cache value in this position.
+     */
     public volatile CacheValue<KeyType, ValueType> front, back;
+    
+    /**
+     * Whether or not this value is detached from the cache's hashmap.
+     */
+    public volatile boolean detached;
 }