io.streamnative.pulsar.handlers.kop.utils.delayed.DelayedOperation Maven / Gradle / Ivy
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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 io.streamnative.pulsar.handlers.kop.utils.delayed;
import io.streamnative.pulsar.handlers.kop.utils.timer.TimerTask;
import java.util.Optional;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import lombok.extern.slf4j.Slf4j;
/**
* An operation whose processing needs to be delayed for at most the given delayMs. For example
* a delayed produce operation could be waiting for specified number of acks; or
* a delayed fetch operation could be waiting for a given number of bytes to accumulate.
*
* The logic upon completing a delayed operation is defined in onComplete() and will be called exactly once.
* Once an operation is completed, isCompleted() will return true. onComplete() can be triggered by either
* forceComplete(), which forces calling onComplete() after delayMs if the operation is not yet completed,
* or tryComplete(), which first checks if the operation can be completed or not now, and if yes calls
* forceComplete().
*
*
A subclass of DelayedOperation needs to provide an implementation of both onComplete() and tryComplete().
*/
@Slf4j
public abstract class DelayedOperation extends TimerTask {
protected final Optional lockOpt;
private final AtomicBoolean completed = new AtomicBoolean(false);
private final AtomicBoolean tryCompletePending = new AtomicBoolean(false);
final Lock lock;
protected DelayedOperation(long delayMs,
Optional lockOpt) {
super(delayMs);
this.lockOpt = lockOpt;
this.lock = lockOpt.orElseGet(() -> new ReentrantLock());
}
/**
* Force completing the delayed operation, if not already completed.
* This function can be triggered when
*
* 1. The operation has been verified to be completable inside tryComplete()
* 2. The operation has expired and hence needs to be completed right now
*
*
Return true iff the operation is completed by the caller: note that
* concurrent threads can try to complete the same operation, but only
* the first thread will succeed in completing the operation and return
* true, others will still return false
*/
public boolean forceComplete() {
if (completed.compareAndSet(false, true)) {
// cancel the timeout timer
cancel();
onComplete();
return true;
} else {
return false;
}
}
/**
* Check if the delayed operation is already completed.
*/
public boolean isCompleted() {
return completed.get();
}
/**
* Call-back to execute when a delayed operation gets expired and hence forced to complete.
*/
public abstract void onExpiration();
/**
* Process for completing an operation. This function needs to be defined
* in subclasses and will be called exactly once in forceComplete()
*/
public abstract void onComplete();
/**
* Try to complete the delayed operation by first checking if the operation
* can be completed by now. If yes execute the completion logic by calling
* forceComplete() and return true iff forceComplete returns true; otherwise return false
*
*
This function needs to be defined in subclasses.
*/
public abstract boolean tryComplete();
/**
* Thread-safe variant of tryComplete() that attempts completion only if the lock can be acquired
* without blocking.
*
*
If threadA acquires the lock and performs the check for completion before completion criteria is met
* and threadB satisfies the completion criteria, but fails to acquire the lock because threadA has not
* yet released the lock, we need to ensure that completion is attempted again without blocking threadA
* or threadB. `tryCompletePending` is set by threadB when it fails to acquire the lock and at least one
* of threadA or threadB will attempt completion of the operation if this flag is set. This ensures that
* every invocation of `maybeTryComplete` is followed by at least one invocation of `tryComplete` until
* the operation is actually completed.
*/
boolean maybeTryComplete() {
boolean retry = false;
boolean done = false;
do {
if (lock.tryLock()) {
try {
tryCompletePending.set(false);
done = tryComplete();
} finally {
lock.unlock();
}
// While we were holding the lock, another thread may have invoked `maybeTryComplete` and set
// `tryCompletePending`. In this case we should retry.
retry = tryCompletePending.get();
} else {
// Another thread is holding the lock. If `tryCompletePending` is already set and this thread failed to
// acquire the lock, then the thread that is holding the lock is guaranteed to see the flag and retry.
// Otherwise, we should set the flag and retry on this thread since the thread holding the lock may have
// released the lock and returned by the time the flag is set.
retry = !tryCompletePending.getAndSet(true);
}
} while (!isCompleted() && retry);
return done;
}
/**
* run() method defines a task that is executed on timeout.
*/
@Override
public void run() {
if (forceComplete()) {
onExpiration();
}
}
}