From 296cb7484761a05f7d97841aca0f9ef725cb8076 Mon Sep 17 00:00:00 2001
From: Joel Dice <joel.dice@gmail.com>
Date: Thu, 29 Sep 2011 18:26:50 -0600
Subject: [PATCH] add bare-bones ConcurrentLinkedQueue implementation

---
 classpath/avian/Atomic.java                   | 10 +++
 .../concurrent/ConcurrentLinkedQueue.java     | 88 +++++++++++++++++++
 src/classpath-avian.cpp                       | 27 ++++++
 3 files changed, 125 insertions(+)
 create mode 100644 classpath/avian/Atomic.java
 create mode 100644 classpath/java/util/concurrent/ConcurrentLinkedQueue.java

diff --git a/classpath/avian/Atomic.java b/classpath/avian/Atomic.java
new file mode 100644
index 0000000000..1d6ee7569e
--- /dev/null
+++ b/classpath/avian/Atomic.java
@@ -0,0 +1,10 @@
+package avian;
+
+import java.lang.reflect.Field;
+
+public class Atomic {
+  public static native long getOffset(Field field);
+
+  public static native boolean compareAndSwapObject
+    (Object o, long offset, Object old, Object new_);
+}
diff --git a/classpath/java/util/concurrent/ConcurrentLinkedQueue.java b/classpath/java/util/concurrent/ConcurrentLinkedQueue.java
new file mode 100644
index 0000000000..aa920311ca
--- /dev/null
+++ b/classpath/java/util/concurrent/ConcurrentLinkedQueue.java
@@ -0,0 +1,88 @@
+package java.util.concurrent;
+
+import avian.Atomic;
+
+public class ConcurrentLinkedQueue<T> {
+  private static final long QueueHead;
+  private static final long QueueTail;
+  private static final long NodeNext;
+
+  static {
+    try {
+      QueueHead = Atomic.getOffset
+        (ConcurrentLinkedQueue.class.getField("head"));
+
+      QueueTail = Atomic.getOffset
+        (ConcurrentLinkedQueue.class.getField("tail"));
+
+      NodeNext = Atomic.getOffset
+        (Node.class.getField("next"));
+    } catch (NoSuchFieldException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  private volatile Node<T> head = new Node(null, null);
+  private volatile Node<T> tail = head;
+
+  public boolean add(T value) {
+    Node<T> n = new Node(value, null);
+    while (true) {
+      Node<T> t = tail;
+      Node<T> next = tail.next;
+      if (t == tail) {
+        if (next != null) {
+          Atomic.compareAndSwapObject(this, QueueTail, t, next);
+        } else if (Atomic.compareAndSwapObject(tail, NodeNext, null, n)) {
+          Atomic.compareAndSwapObject(this, QueueTail, t, n);
+          break;
+        }
+      }
+    }
+
+    return true;
+  }
+
+  public T peek() {
+    return poll(false);
+  }
+
+  public T poll() {
+    return poll(true);
+  }
+
+  public T poll(boolean remove) {
+    while (true) {
+      Node<T> h = head;
+      Node<T> t = tail;
+      Node<T> next = head.next;
+
+      if (h == head) {
+        if (h == t) {
+          if (next != null) {
+            Atomic.compareAndSwapObject(this, QueueTail, t, next);
+          } else {
+            return null;
+          }
+        } else {
+          T value = next.value;
+          if ((! remove)
+              || Atomic.compareAndSwapObject(this, QueueHead, h, next))
+          {
+            return value;
+          }
+        }
+      }
+    }
+  }
+
+  private static class Node<T> {
+    public volatile T value;
+    public volatile Node<T> next;
+
+    public Node(T value, Node<T> next) {
+      this.value = value;
+      this.next = next;
+    }
+  }
+}
diff --git a/src/classpath-avian.cpp b/src/classpath-avian.cpp
index 7d806ce87e..39cde4ff83 100644
--- a/src/classpath-avian.cpp
+++ b/src/classpath-avian.cpp
@@ -605,6 +605,33 @@ Avian_java_lang_Thread_yield
   t->m->system->yield();
 }
 
+extern "C" JNIEXPORT int64_t JNICALL
+Avian_avian_Atomic_getOffset
+(Thread* t, object, uintptr_t* arguments)
+{
+  return fieldOffset
+    (t, jfieldVmField(t, reinterpret_cast<object>(arguments[0])));
+}
+
+extern "C" JNIEXPORT int64_t JNICALL
+Avian_avian_Atomic_compareAndSwapObject
+(Thread* t, object, uintptr_t* arguments)
+{
+  object target = reinterpret_cast<object>(arguments[0]);
+  int64_t offset; memcpy(&offset, arguments + 1, 8);
+  uintptr_t expect = arguments[3];
+  uintptr_t update = arguments[4];
+
+  bool success = atomicCompareAndSwap
+    (&cast<uintptr_t>(target, offset), expect, update);
+
+  if (success) {
+    mark(t, target, offset);
+  }
+
+  return success;
+}
+
 extern "C" JNIEXPORT int64_t JNICALL
 Avian_avian_Classes_primitiveClass
 (Thread* t, object, uintptr_t* arguments)