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Add a ConcurrentLinkedStack, based on WFIStack
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jctools-experimental/src/main/java/org/jctools/stacks/ConcurrentLinkedStack.java
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/* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* http://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
package org.jctools.stacks; | ||
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import java.util.Iterator; | ||
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/** | ||
* A concurrent, unbounded, and non-blocking stack based on linked nodes. | ||
* Concurrent push and pop executes safely across multiple threads. | ||
* <p> | ||
* Unlike {@code java.util.concurrent.ConcurrentLinkedDeque}, this class only supports | ||
* the stack APIs, and does not support internal-remove. | ||
* On the other hand, this class has a constant time {@link #size()} method, | ||
* and a wait-free {@link #push(Object)} method. | ||
* <p> | ||
* The {@link #iterator()} operates on a safely captured snapshot of the stack, | ||
* and is <em>weakly consistent</em>. This follows the precedent of the | ||
* {@code java.util.concurrent} package, as defined in its package summary. | ||
* <p> | ||
* This implementation is based on the {@link WFIStack}. | ||
*/ | ||
public class ConcurrentLinkedStack<T> implements Iterable<T> | ||
{ | ||
private final WFIStack<LinkedNode<T>> stack; | ||
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/** | ||
* Create a new empty stack. | ||
*/ | ||
public ConcurrentLinkedStack() | ||
{ | ||
stack = new WFIStack<>(); | ||
} | ||
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/** | ||
* Push the given object onto the stack. | ||
* | ||
* @param value The object to push onto the stack. | ||
*/ | ||
public void push(T value) | ||
{ | ||
stack.push(new LinkedNode<>(value)); | ||
} | ||
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/** | ||
* Pop the top-most object from the stack. | ||
* | ||
* @return The object that was the head of the stack, or {@code null} if the stack was empty. | ||
*/ | ||
public T pop() | ||
{ | ||
LinkedNode<T> node = stack.pop(); | ||
return node == null ? null : node.value; | ||
} | ||
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/** | ||
* Peek at the top of the stack, without removing said object. | ||
* <p> | ||
* Note that the result may be outdated as soon as this method returns. | ||
* | ||
* @return The object that is the top of the stack, or {@code null} if the stack is empty. | ||
*/ | ||
public T peek() | ||
{ | ||
LinkedNode<T> node = stack.peek(); | ||
return node == null ? null : node.value; | ||
} | ||
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/** | ||
* Get the size of the stack. | ||
* | ||
* @return The number of objects on this stack. | ||
*/ | ||
public int size() | ||
{ | ||
return stack.size(); | ||
} | ||
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/** | ||
* Tell whether the stack is empty. | ||
* | ||
* @return {@code true} if the stack is empty. | ||
*/ | ||
public boolean isEmpty() | ||
{ | ||
return stack.isEmpty(); | ||
} | ||
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@Override | ||
public Iterator<T> iterator() | ||
{ | ||
return new Iterator<T>() | ||
{ | ||
private final Iterator<LinkedNode<T>> inner = stack.iterator(); | ||
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@Override | ||
public boolean hasNext() | ||
{ | ||
return inner.hasNext(); | ||
} | ||
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@Override | ||
public T next() | ||
{ | ||
LinkedNode<T> next = inner.next(); | ||
return next.value; | ||
} | ||
}; | ||
} | ||
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private static class LinkedNode<T> extends WFIStack.Node | ||
{ | ||
private final T value; | ||
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private LinkedNode(T value) | ||
{ | ||
this.value = value; | ||
} | ||
} | ||
} |
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jctools-experimental/src/test/java/org/jctools/stacks/ConcurrentLinkedStackTest.java
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/* | ||
* Licensed under the Apache License, Version 2.0 (the "License"); | ||
* you may not use this file except in compliance with the License. | ||
* You may obtain a copy of the License at | ||
* | ||
* http://www.apache.org/licenses/LICENSE-2.0 | ||
* | ||
* Unless required by applicable law or agreed to in writing, software | ||
* distributed under the License is distributed on an "AS IS" BASIS, | ||
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
* See the License for the specific language governing permissions and | ||
* limitations under the License. | ||
*/ | ||
package org.jctools.stacks; | ||
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import org.junit.Test; | ||
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import java.util.Iterator; | ||
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import static org.junit.Assert.*; | ||
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/** | ||
* @see WFIStackTest most of the correctness of this implementation is derived from the WFIStack. | ||
*/ | ||
public class ConcurrentLinkedStackTest | ||
{ | ||
@Test | ||
public void sanityCheckMethods() | ||
{ | ||
ConcurrentLinkedStack<Object> stack = new ConcurrentLinkedStack<Object>(); | ||
assertTrue(stack.isEmpty()); | ||
assertEquals(0, stack.size()); | ||
assertFalse(stack.iterator().hasNext()); | ||
assertNull(stack.pop()); | ||
assertNull(stack.peek()); | ||
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stack.push(1); | ||
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assertEquals(1, stack.peek()); | ||
assertFalse(stack.isEmpty()); | ||
assertEquals(1, stack.size()); | ||
Iterator<Object> iterator = stack.iterator(); | ||
assertTrue(iterator.hasNext()); | ||
assertEquals(1, iterator.next()); | ||
assertFalse(iterator.hasNext()); | ||
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assertEquals(1, stack.pop()); | ||
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assertTrue(stack.isEmpty()); | ||
assertEquals(0, stack.size()); | ||
assertFalse(stack.iterator().hasNext()); | ||
assertNull(stack.pop()); | ||
assertNull(stack.peek()); | ||
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stack.push(2); | ||
stack.push(3); | ||
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assertFalse(stack.isEmpty()); | ||
assertEquals(2, stack.size()); | ||
iterator = stack.iterator(); | ||
assertTrue(iterator.hasNext()); | ||
assertEquals(3, iterator.next()); | ||
assertTrue(iterator.hasNext()); | ||
assertEquals(2, iterator.next()); | ||
assertFalse(iterator.hasNext()); | ||
assertEquals(3, stack.peek()); | ||
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assertEquals(3, stack.pop()); | ||
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assertEquals(2, stack.peek()); | ||
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assertEquals(2, stack.pop()); | ||
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assertTrue(stack.isEmpty()); | ||
assertEquals(0, stack.size()); | ||
assertFalse(stack.iterator().hasNext()); | ||
assertNull(stack.pop()); | ||
assertNull(stack.peek()); | ||
} | ||
} |