A concurrent linked list, to replace the array list of old roots (work in progress)

h2/src/main/org/h2/mvstore/ConcurrentLinkedList.java

@@ -41,24 +41,31 @@ public class ConcurrentLinkedList<K> {
     
     public void removeFirst(K obj) {
         Entry<K> x = head;
-        if (x == null || tail == x) {
-            throw DataUtils.newUnsupportedOperationException(
-                    "Must contain at least two entries");
+        if (x == null) {
+            return;
         }
         if (x.obj.equals(obj)) {
+            if (head == tail) {
+                tail = x.next;
+            }
             head = x.next;
         }
     }
 
     public void removeLast(K obj) {
         Entry<K> x = head;
-        Entry<K> prev = x;
+        if (x == null) {
+            return;
+        }
+        Entry<K> prev = null;
         while (x.next != null) {
             prev = x;
             x = x.next;
         }
         if (x.obj.equals(obj)) {
-            prev.next = null;
+            if (prev != null) {
+                prev.next = null;
+            }
             if (head == tail) {
                 head = prev;
             }

h2/src/main/org/h2/mvstore/MVMap.java

@@ -996,12 +996,8 @@ public class MVMap<K, V> extends AbstractMap<K, V>
             return;
         }
         Page last = oldRootsList.peekLast();
-        if (oldRootsList.peekFirst() == last) {
-            // do nothing if there is no or only one entry
-            return;
-        }
-        ;
         // TODO why is this?
+        ;
         oldest--;
         while (true) {
             Page p = oldRootsList.peekFirst();

h2/src/test/org/h2/test/store/TestConcurrentLinkedList.java

@@ -13,6 +13,9 @@ import org.h2.mvstore.ConcurrentLinkedList;
 import org.h2.test.TestBase;
 import org.h2.util.Task;
 
+/**
+ * Test the concurrent linked list.
+ */
 public class TestConcurrentLinkedList extends TestBase {
 
     /**
@@ -21,19 +24,24 @@ public class TestConcurrentLinkedList extends TestBase {
      * @param a ignored
      */
     public static void main(String... a) throws Exception {
-        TestBase.createCaller().init().test();
+        TestConcurrentLinkedList test = (TestConcurrentLinkedList) TestBase.createCaller().init();
+        test.test();
+        test.testPerformance();
     }
 
     @Override
     public void test() throws Exception {
+        testConcurrent();
+        testRandomized();
+    }
+    
+    private void testPerformance() {
         testPerformance(true);
         testPerformance(false);
         testPerformance(true);
         testPerformance(false);
         testPerformance(true);
         testPerformance(false);
-        testConcurrent();
-        testRandomized();
     }
     
     private void testPerformance(final boolean stock) {
@@ -100,64 +108,49 @@ public class TestConcurrentLinkedList extends TestBase {
             LinkedList<Integer> x = new LinkedList<Integer>();
             StringBuilder buff = new StringBuilder();
             for (int j = 0; j < 10000; j++) {
-                int opType = r.nextInt(10);
+                buff.append("[" + j + "] ");
+                int opType = r.nextInt(3);
                 switch (opType) {
                 case 0: {
                     int value = r.nextInt(100);
-                    buff.append(" add " + value);
+                    buff.append("add " + value + "\n");
                     test.add(value);
                     x.add(value);
                     break;
                 }
                 case 1: {
                     Integer value = x.peek();
-                    buff.append(" peek");
-                    if (value == null) {
-                        assertNull(test.peekFirst());
+                    if (value != null && r.nextBoolean()) {
+                        buff.append("removeFirst\n");
+                        x.removeFirst();
+                        test.removeFirst(value);
                     } else {
-                        assertEquals(value.intValue(), test.peekFirst().intValue());
+                        buff.append("removeFirst -1\n");
+                        test.removeFirst(-1);
                     }
                     break;
                 }
                 case 2: {
                     Integer value = x.peekLast();
-                    buff.append(" peeLast");
-                    if (value == null) {
-                        assertNull(test.peekLast());
+                    if (value != null && r.nextBoolean()) {
+                        buff.append("removeLast\n");
+                        x.removeLast();
+                        test.removeLast(value);
                     } else {
-                        assertEquals(value.intValue(), test.peekLast()
-                                .intValue());
-                    }
-                    break;
-                }
-                case 3: {
-                    if (x.size() >= 2) {
-                        Integer value = x.peek();
-                        if (value != null && r.nextBoolean()) {
-                            buff.append(" removeFirst");
-                            x.removeFirst();
-                            test.removeFirst(value);
-                        } else {
-                            test.removeFirst(-1);
-                        }
-                    }
-                    break;
-                }
-                case 4: {
-                    if (x.size() >= 2) {
-                        Integer value = x.peekLast();
-                        if (value != null && r.nextBoolean()) {
-                            buff.append(" removeLast");
-                            x.removeLast();
-                            test.removeLast(value);
-                        } else {
-                            test.removeLast(-1);
-                        }
+                        buff.append("removeLast -1\n");
+                        test.removeLast(-1);
                     }
                     break;
                 }
                 }
                 assertEquals(toString(x.iterator()), toString(test.iterator()));
+                if (x.isEmpty()) {
+                    assertNull(test.peekFirst());
+                    assertNull(test.peekLast());
+                } else {
+                    assertEquals(x.peekFirst().intValue(), test.peekFirst().intValue());
+                    assertEquals(x.peekLast().intValue(), test.peekLast().intValue());
+                }
             }
         }
     }