Linkedblockingqueue source code analysis - initialization

LinkedBlockingQueue characteristic

LinkedBlockingQueue It is usually called linked list blocking queue , From the naming, we can know , The underlying data is a linked list , And the queue can be blocked .LinkedBlockingQueue Characteristics ：

• Blocking queue based on linked list , The underlying data structure is a linked list

• First in first out queue based on linked list , New elements at the end of the team , Get the elements from the team head

• The size of the linked list can be set during initialization , The default is  Integer  The maximum of

• have access to Iterator  To iterate

attribute

Source code ：

public class LinkedBlockingQueue<E> extends AbstractQueue<E>
 implements BlockingQueue<E>, java.io.Serializable {
 private static final long serialVersionUID = -6903933977591709194L;
 
 /**
 * Linked list node class
 */
 static class Node<E> {
 E item;

 /**
 * One of:
 * - the real successor Node
 * - this Node, meaning the successor is head.next
 * - null, meaning there is no successor (this is the last node)
 */
 Node<E> next;

 Node(E x) { item = x; }
 }
 
 
 /** The capacity bound, or Integer.MAX_VALUE if none */
 private final int capacity;

 /** Current number of elements */
 private final AtomicInteger count = new AtomicInteger();

 /**
 * Head of linked list.
 * Invariant: head.item == null
 */
 transient Node<E> head;

 /**
 * Tail of linked list.
 * Invariant: last.next == null
 */
 private transient Node<E> last;

 /** Lock held by take, poll, etc */
 private final ReentrantLock takeLock = new ReentrantLock();

 /** Wait queue for waiting takes */
 private final Condition notEmpty = takeLock.newCondition();

 /** Lock held by put, offer, etc */
 private final ReentrantLock putLock = new ReentrantLock();

 /** Wait queue for waiting puts */
 private final Condition notFull = putLock.newCondition();

 ......
}


static class Node<E>

  Represents the element node of the linked list

Node<E> next;

  Indicates the next node pointed to by the current element , If null, It means that the current node is the last node

private final int capacity;

The capacity of the list , Default  Integer.MAX_VALUE

private final AtomicInteger count = new AtomicInteger();

The linked list already has element size , Use  AtomicInteger, So it's thread safe

transient Node<E> head;

  Chain head

private transient Node<E> last;

Chain tail

private final ReentrantLock takeLock = new ReentrantLock();

 take  Time lock

private final Condition notEmpty = takeLock.newCondition();

take  The condition queue of

private final ReentrantLock putLock = new ReentrantLock();

put  Time lock

private final Condition notFull = putLock.newCondition();

put  The condition queue of

summary ：

Designed two locks , One is take lock , One is put lock , The purpose is to make the two operations not interfere with each other , A simultaneous

initialization

Source code ：

 public LinkedBlockingQueue() {
 this(Integer.MAX_VALUE);
 }

 public LinkedBlockingQueue(int capacity) {
 if (capacity <= 0) throw new IllegalArgumentException();
 this.capacity = capacity;
 last = head = new Node<E>(null);
 }

 public LinkedBlockingQueue(Collection<? extends E> c) {
 this(Integer.MAX_VALUE);
 final ReentrantLock putLock = this.putLock;
 putLock.lock(); // Never contended, but necessary for visibility
 try {
 int n = 0;
 for (E e : c) {
 if (e == null)
 throw new NullPointerException();
 if (n == capacity)
 throw new IllegalStateException(&quot;Queue full&quot;);
 enqueue(new Node<E>(e));
 ++n;
 }
 count.set(n);
 } finally {
 putLock.unlock();
 }
 }


Three initialization methods are provided in the source code ： The first one is ： Use default  Integer  The second is to initialize with the maximum value of ： Specify the capacity of the linked list and initialize Chapter 3 ： Initialize with existing set data