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本文主要研究一下artemis的ClientProducerCredits
ClientProducerCredits
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/ClientProducerCredits.java
public interface ClientProducerCredits {
void acquireCredits(int credits) throws ActiveMQException;
void receiveCredits(int credits);
void receiveFailCredits(int credits);
boolean isBlocked();
void init(SessionContext sessionContext);
void reset();
void close();
void incrementRefCount();
int decrementRefCount();
void releaseOutstanding();
SimpleString getAddress();
}
- ClientProducerCredits接口定义了acquireCredits、receiveCredits、receiveFailCredits、isBlocked、init、reset、close、incrementRefCount、decrementRefCount、releaseOutstanding、getAddress方法
AbstractProducerCreditsImpl
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/AbstractProducerCreditsImpl.java
public abstract class AbstractProducerCreditsImpl implements ClientProducerCredits {
protected int pendingCredits;
private final int windowSize;
protected volatile boolean closed;
protected boolean blocked;
protected final SimpleString address;
private final ClientSessionInternal session;
protected int arriving;
private int refCount;
protected boolean serverRespondedWithFail;
protected SessionContext sessionContext;
public AbstractProducerCreditsImpl(final ClientSessionInternal session,
final SimpleString address,
final int windowSize) {
this.session = session;
this.address = address;
this.windowSize = windowSize / 2;
}
@Override
public SimpleString getAddress() {
return address;
}
@Override
public void init(SessionContext sessionContext) {
// We initial request twice as many credits as we request in subsequent requests
// This allows the producer to keep sending as more arrive, minimising pauses
checkCredits(windowSize);
this.sessionContext = sessionContext;
this.sessionContext.linkFlowControl(address, this);
}
@Override
public void acquireCredits(final int credits) throws ActiveMQException {
checkCredits(credits);
actualAcquire(credits);
afterAcquired(credits);
}
protected void afterAcquired(int credits) throws ActiveMQAddressFullException {
// check to see if the blocking mode is FAIL on the server
synchronized (this) {
pendingCredits -= credits;
}
}
protected abstract void actualAcquire(int credits);
@Override
public boolean isBlocked() {
return blocked;
}
@Override
public void receiveFailCredits(final int credits) {
serverRespondedWithFail = true;
// receive credits like normal to keep the sender from blocking
receiveCredits(credits);
}
@Override
public void receiveCredits(final int credits) {
synchronized (this) {
arriving -= credits;
}
}
@Override
public synchronized void reset() {
// Any pendingCredits credits from before failover won't arrive, so we re-initialise
int beforeFailure = pendingCredits;
pendingCredits = 0;
arriving = 0;
// If we are waiting for more credits than what's configured, then we need to use what we tried before
// otherwise the client may starve as the credit will never arrive
checkCredits(Math.max(windowSize * 2, beforeFailure));
}
@Override
public void close() {
// Closing a producer that is blocking should make it return
closed = true;
}
@Override
public synchronized void incrementRefCount() {
refCount++;
}
@Override
public synchronized int decrementRefCount() {
return --refCount;
}
public abstract int getBalance();
protected void checkCredits(final int credits) {
int needed = Math.max(credits, windowSize);
int toRequest = -1;
synchronized (this) {
if (getBalance() + arriving < needed) {
toRequest = needed - arriving;
pendingCredits += toRequest;
arriving += toRequest;
}
}
if (toRequest != -1) {
requestCredits(toRequest);
}
}
private void requestCredits(final int credits) {
session.sendProducerCreditsMessage(credits, address);
}
}
- AbstractProducerCreditsImpl实现了ClientProducerCredits的部分方法；其构造器接收session、address、windowSize参数；其init方法首先执行checkCredits，然后执行sessionContext.linkFlowControl(address, this)
- acquireCredits方法先执行checkCredits，在执行actualAcquire及afterAcquired方法；afterAcquired方法会从pendingCredits扣减credits；receiveFailCredits方法设置serverRespondedWithFail为true，然后执行receiveCredits方法；receiveCredits方法会从arriving扣减credits；reset方法会重置pendingCredits、arriving，然后执行checkCredits方法
- checkCredits方法先计算needed，再计算toRequest同时更新pendingCredits及arriving；在toRequest不为-1时会执行requestCredits方法；requestCredits方法执行的是session.sendProducerCreditsMessage(credits, address)方法
ClientProducerCreditsImpl
activemq-artemis-2.11.0/artemis-core-client/src/main/java/org/apache/activemq/artemis/core/client/impl/ClientProducerCreditsImpl.java
public class ClientProducerCreditsImpl extends AbstractProducerCreditsImpl {
private final Semaphore semaphore;
public ClientProducerCreditsImpl(ClientSessionInternal session, SimpleString address, int windowSize) {
super(session, address, windowSize);
// Doesn't need to be fair since session is single threaded
semaphore = new Semaphore(0, false);
}
@Override
protected void afterAcquired(int credits) throws ActiveMQAddressFullException {
// check to see if the blocking mode is FAIL on the server
synchronized (this) {
super.afterAcquired(credits);
if (serverRespondedWithFail) {
serverRespondedWithFail = false;
// remove existing credits to force the client to ask the server for more on the next send
semaphore.drainPermits();
pendingCredits = 0;
arriving = 0;
throw ActiveMQClientMessageBundle.BUNDLE.addressIsFull(address.toString(), credits);
}
}
}
@Override
protected void actualAcquire(int credits) {
boolean tryAcquire;
synchronized (this) {
tryAcquire = semaphore.tryAcquire(credits);
}
if (!tryAcquire && !closed) {
this.blocked = true;
try {
while (!semaphore.tryAcquire(credits, 10, TimeUnit.SECONDS)) {
// I'm using string concatenation here in case address is null
// better getting a "null" string than a NPE
ActiveMQClientLogger.LOGGER.outOfCreditOnFlowControl("" + address);
}
} catch (InterruptedException interrupted) {
Thread.currentThread().interrupt();
throw new ActiveMQInterruptedException(interrupted);
} finally {
this.blocked = false;
}
}
}
@Override
public synchronized void reset() {
// Any pendingCredits credits from before failover won't arrive, so we re-initialise
semaphore.drainPermits();
super.reset();
}
@Override
public void close() {
super.close();
// Closing a producer that is blocking should make it return
semaphore.release(Integer.MAX_VALUE / 2);
}
@Override
public void receiveCredits(final int credits) {
synchronized (this) {
super.receiveCredits(credits);
}
semaphore.release(credits);
}
@Override
public synchronized void releaseOutstanding() {
semaphore.drainPermits();
}
@Override
public int getBalance() {
return semaphore.availablePermits();
}
}
- ClientProducerCreditsImpl继承了AbstractProducerCreditsImpl，其构造器创建了permits为0，fair为false的Semaphore；afterAcquired方法在serverRespondedWithFail为true时会执行semaphore.drainPermits()然后抛出ActiveMQClientMessageBundle.BUNDLE.addressIsFull(address.toString(), credits)
- actualAcquire方法会先执行semaphore.tryAcquire(credits)，若为false则设置blocked为true，然后一直while循环semaphore.tryAcquire(credits, 10, TimeUnit.SECONDS)直到为true，最后再finally设置blocked为false
- receiveCredits方法主要是执行semaphore.release(credits)；getBalance方法返回的是semaphore.availablePermits()；releaseOutstanding执行的是semaphore.release(credits)；reset方法执行的是semaphore.drainPermits()；close方法执行的是 semaphore.release(Integer.MAX_VALUE / 2)
小结
- AbstractProducerCreditsImpl实现了ClientProducerCredits的部分方法；其构造器接收session、address、windowSize参数；其init方法首先执行checkCredits，然后执行sessionContext.linkFlowControl(address, this)
- acquireCredits方法先执行checkCredits，在执行actualAcquire及afterAcquired方法；afterAcquired方法会从pendingCredits扣减credits；receiveFailCredits方法设置serverRespondedWithFail为true，然后执行receiveCredits方法；receiveCredits方法会从arriving扣减credits；reset方法会重置pendingCredits、arriving，然后执行checkCredits方法
- checkCredits方法先计算needed，再计算toRequest同时更新pendingCredits及arriving；在toRequest不为-1时会执行requestCredits方法；requestCredits方法执行的是session.sendProducerCreditsMessage(credits, address)方法
