Rewrote the stack to support elimination & combining backoff strategies

Eliminaton cancels out opposite operations (push and pop). Combining
merges similar operations (pushes) into a batch operation. Both use an
arena to transfer elements between threads as a backoff strategy when
the stack's top reference is contended (CAS failed). This greatly
improves scalability by reducing the number of threads contending on
a shared reference.

The approach taken is much simpler than the previous EliminationStack
or the DECS paper's algorithm. Both of the alternatives rely on multiple
arena states to model different scenarios. In this version, the arena slot
is either empty or full. The consumer may receive multiple elements and it
mimics a producer after taking one of the elements for itself. This greatly
simplifies the DECS algorithm, resulting in higher performance despite a
penalty incurred by the consumer when producing.

caffeine/src/jmh/java/com/github/benmanes/caffeine/EliminationStackBenchmark.java → caffeine/src/jmh/java/com/github/benmanes/caffeine/ConcurrentLinkedStackBenchmark.java

@@ -31,10 +31,8 @@
  * @author [email protected] (Ben Manes)
  */
 @State(Scope.Group)
-public class EliminationStackBenchmark {
-  @Param({"EliminationStack", "ConcurrentLinkedQueue", "ArrayBlockingQueue",
-    "LinkedBlockingQueueBenchmark", "LinkedTransferQueue", "SynchronousQueue",
-    "SynchronizedArrayDeque"})
+public class ConcurrentLinkedStackBenchmark {
+  @Param({"ConcurrentLinkedStack_linearizable", "ConcurrentLinkedQueue"})
   QueueType queueType;
 
   Queue<Boolean> queue;
@@ -44,23 +42,23 @@ public void setup() {
     queue = queueType.create();
   }
 
-  @Benchmark @Group("no_contention") @GroupThreads(1)
-  public void no_contention_offer() {
+  @Benchmark @Group("low_contention") @GroupThreads(1)
+  public void low_contention_offer() {
     queue.offer(Boolean.TRUE);
   }
 
-  @Benchmark @Group("no_contention") @GroupThreads(1)
-  public void no_contention_poll() {
+  @Benchmark @Group("low_contention") @GroupThreads(1)
+  public void low_contention_poll() {
     queue.poll();
   }
 
-  @Benchmark @Group("mild_contention") @GroupThreads(4)
-  public void mild_contention_offer() {
+  @Benchmark @Group("medium_contention") @GroupThreads(4)
+  public void medium_contention_offer() {
     queue.offer(Boolean.TRUE);
   }
 
-  @Benchmark @Group("mild_contention") @GroupThreads(4)
-  public void mild_contention_poll() {
+  @Benchmark @Group("medium_contention") @GroupThreads(4)
+  public void medium_contention_poll() {
     queue.poll();
   }
 

caffeine/src/jmh/java/com/github/benmanes/caffeine/QueueType.java

@@ -32,7 +32,8 @@
 public enum QueueType {
   SingleConsumerQueue_optimistic(SingleConsumerQueue::optimistic),
   SingleConsumerQueue_linearizable(SingleConsumerQueue::linearizable),
-  EliminationStack(() -> new EliminationStack<>().asLifoQueue()),
+  ConcurrentLinkedStack_optimistic(() -> ConcurrentLinkedStack.optimistic().asLifoQueue()),
+  ConcurrentLinkedStack_linearizable(() -> ConcurrentLinkedStack.linearizable().asLifoQueue()),
   ConcurrentLinkedQueue(ConcurrentLinkedQueue<Object>::new),
   ArrayBlockingQueue(() -> new ArrayBlockingQueue<>(10000)),
   LinkedBlockingQueueBenchmark(LinkedBlockingQueue<Object>::new),

caffeine/src/jmh/java/com/github/benmanes/caffeine/SingleConsumerQueueBenchmark.java

@@ -33,9 +33,7 @@
  */
 @State(Scope.Group)
 public class SingleConsumerQueueBenchmark {
-  @Param({"SingleConsumerQueue_optimistic",
-    "SingleConsumerQueue_linearizable",
-    "ConcurrentLinkedQueue"})
+  @Param({"SingleConsumerQueue_linearizable", "ConcurrentLinkedQueue"})
   QueueType queueType;
 
   Queue<Boolean> queue;
@@ -71,7 +69,7 @@ public void high_contention_offer() {
   }
 
   @Benchmark @Group("high_contention") @GroupThreads(1)
-  public void high_contention_poll() {
+  public void high_contention_clear() {
     queue.clear();
   }
 }

caffeine/src/jmh/java/com/github/benmanes/caffeine/profiler/EliminationStackProfiler.java → caffeine/src/jmh/java/com/github/benmanes/caffeine/profiler/ConcurrentLinkedStackProfiler.java

@@ -17,15 +17,15 @@
 
 import java.util.concurrent.ThreadLocalRandom;
 
-import com.github.benmanes.caffeine.EliminationStack;
+import com.github.benmanes.caffeine.ConcurrentLinkedStack;
 
 /**
  * @author Ben Manes ([email protected])
  */
-public final class EliminationStackProfiler extends ProfilerHook {
+public final class ConcurrentLinkedStackProfiler extends ProfilerHook {
   static final Integer ELEMENT = 1;
 
-  final EliminationStack<Integer> stack = new EliminationStack<>();
+  final ConcurrentLinkedStack<Integer> stack = ConcurrentLinkedStack.linearizable();
 
   @Override
   protected void profile() {
@@ -41,7 +41,7 @@ protected void profile() {
   }
 
   public static void main(String[] args) {
-    ProfilerHook profile = new EliminationStackProfiler();
+    ProfilerHook profile = new ConcurrentLinkedStackProfiler();
     profile.run();
   }
 }