序
本文主要研究一下artemis message的priority
priority
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/message/impl/CoreMessage.java
public class CoreMessage extends RefCountMessage implements ICoreMessage {
//......
protected byte priority;
public byte getPriority() {
return priority;
}
public CoreMessage setPriority(byte priority) {
this.priority = priority;
messageChanged();
return this;
}
//......
}- CoreMessage定义了priority属性(
Values range from 0 (less priority) to 9 (more priority) inclusive)，并提供了getPriority、setPriority方法
messageReferences.add
activemq-artemis-2.11.0/artemis-server/src/main/java/org/apache/activemq/artemis/core/server/impl/QueueImpl.java
public class QueueImpl extends CriticalComponentImpl implements Queue {
//......
private final PriorityLinkedList messageReferences = new PriorityLinkedListImpl<>(QueueImpl.NUM_PRIORITIES, MessageReferenceImpl.getIDComparator());
//......
private synchronized void internalAddTail(final MessageReference ref) {
refAdded(ref);
messageReferences.addTail(ref, getPriority(ref));
pendingMetrics.incrementMetrics(ref);
enforceRing(false);
}
private void internalAddHead(final MessageReference ref) {
queueMemorySize.addAndGet(ref.getMessageMemoryEstimate());
pendingMetrics.incrementMetrics(ref);
refAdded(ref);
int priority = getPriority(ref);
messageReferences.addHead(ref, priority);
ref.setInDelivery(false);
}
private void internalAddSorted(final MessageReference ref) {
queueMemorySize.addAndGet(ref.getMessageMemoryEstimate());
pendingMetrics.incrementMetrics(ref);
refAdded(ref);
int priority = getPriority(ref);
messageReferences.addSorted(ref, priority);
}
private int getPriority(MessageReference ref) {
try {
return ref.getMessage().getPriority();
} catch (Throwable e) {
ActiveMQServerLogger.LOGGER.unableToGetMessagePriority(e);
return 4; // the default one in case of failure
}
}
//......
} - QueueImpl定义了messageReferences，其类型为PriorityLinkedList
；其internalAddTail、internalAddHead、internalAddSorted方法都会调用getPriority方法获取priority，出现异常返回4，之后通过messageReferences的addTail、addHead、addSorted方法添加到队列
PriorityLinkedList
activemq-artemis-2.11.0/artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/PriorityLinkedList.java
public interface PriorityLinkedList {
void addHead(T t, int priority);
void addTail(T t, int priority);
void addSorted(T t, int priority);
T poll();
void clear();
/**
* Returns the size of this list.
* It is safe to be called concurrently.
*/
int size();
LinkedListIterator iterator();
/**
* Returns {@code true} if empty, {@code false} otherwise.
* It is safe to be called concurrently.
*/
boolean isEmpty();
} - PriorityLinkedList接口定义了根据priority的addHead、addTail、addSorted方法，其size以及isEmpty要求是线程安全的
PriorityLinkedListImpl
activemq-artemis-2.11.0/artemis-commons/src/main/java/org/apache/activemq/artemis/utils/collections/PriorityLinkedListImpl.java
public class PriorityLinkedListImpl implements PriorityLinkedList {
private static final AtomicIntegerFieldUpdater SIZE_UPDATER = AtomicIntegerFieldUpdater.newUpdater(PriorityLinkedListImpl.class, "size");
protected LinkedListImpl[] levels;
private volatile int size;
private int lastReset;
private int highestPriority = -1;
private int lastPriority = -1;
public PriorityLinkedListImpl(final int priorities) {
this(priorities, null);
}
public PriorityLinkedListImpl(final int priorities, Comparator comparator) {
levels = (LinkedListImpl[]) Array.newInstance(LinkedListImpl.class, priorities);
for (int i = 0; i < priorities; i++) {
levels[i] = new LinkedListImpl<>(comparator);
}
}
private void checkHighest(final int priority) {
if (lastPriority != priority || priority > highestPriority) {
lastPriority = priority;
if (lastReset == Integer.MAX_VALUE) {
lastReset = 0;
} else {
lastReset++;
}
}
if (priority > highestPriority) {
highestPriority = priority;
}
}
@Override
public void addHead(final T t, final int priority) {
checkHighest(priority);
levels[priority].addHead(t);
exclusiveIncrementSize(1);
}
@Override
public void addTail(final T t, final int priority) {
checkHighest(priority);
levels[priority].addTail(t);
exclusiveIncrementSize(1);
}
@Override
public void addSorted(T t, int priority) {
checkHighest(priority);
levels[priority].addSorted(t);
exclusiveIncrementSize(1);
}
@Override
public T poll() {
T t = null;
// We are just using a simple prioritization algorithm:
// Highest priority refs always get returned first.
// This could cause starvation of lower priority refs.
// TODO - A better prioritization algorithm
for (int i = highestPriority; i >= 0; i--) {
LinkedListImpl ll = levels[i];
if (ll.size() != 0) {
t = ll.poll();
if (t != null) {
exclusiveIncrementSize(-1);
if (ll.size() == 0) {
if (highestPriority == i) {
highestPriority--;
}
}
}
break;
}
}
return t;
}
@Override
public void clear() {
for (LinkedListImpl list : levels) {
list.clear();
}
exclusiveSetSize(0);
}
private void exclusiveIncrementSize(int amount) {
SIZE_UPDATER.lazySet(this, this.size + amount);
}
private void exclusiveSetSize(int value) {
SIZE_UPDATER.lazySet(this, value);
}
@Override
public int size() {
return size;
}
@Override
public boolean isEmpty() {
return size == 0;
}
@Override
public LinkedListIterator iterator() {
return new PriorityLinkedListIterator();
}
//......
} - PriorityLinkedListImpl实现了PriorityLinkedList接口，其构造器需要priorities参数，它使用Array.newInstance(LinkedListImpl.class, priorities)来创建并初始化levels数组，其数组元素类型为LinkedListImpl；其addHead、addTail、addSorted先执行checkHighest(priority)维护highestPriority，之后调用对应priority的LinkedListImpl的addHead、addTail、addSorted方法，最后调用exclusiveIncrementSize方法递增size；其poll方法会从highestPriority的LinkedListImpl开始poll
小结
CoreMessage定义了priority属性(Values range from 0 (less priority) to 9 (more priority) inclusive)，并提供了getPriority、setPriority方法；QueueImpl定义了messageReferences，其类型为PriorityLinkedList