/**
* Best-effort attempt to remove an argument from a batch. This may get invoked when a
* cancellation occurs somewhere downstream. This method finds the first occurrence of an argument
* in the batch, and removes that occurrence.
*
* <p>This is currently O(n). If an O(1) approach is needed, then we need to refactor internals to
* use a Map instead of Queue. My first pass at this is fairly naive, on the suspicion that
* unsubscription will be rare enough to not cause a perf problem.
*
* @param arg argument to remove from batch
*/
/* package-private */ void remove(RequestArgumentType arg) {
if (batchStarted.get()) {
// nothing we can do
return;
}
if (batchLock.readLock().tryLock()) {
try {
/* double-check now that we have the lock - if the batch is started, deleting is useless */
if (batchStarted.get()) {
return;
}
for (CollapsedRequest<ResponseType, RequestArgumentType> collapsedRequest :
batchArgumentQueue) {
if (arg.equals(collapsedRequest.getArgument())) {
batchArgumentQueue.remove(collapsedRequest);
count.decrementAndGet();
return; // just remove a single instance
}
}
} finally {
batchLock.readLock().unlock();
}
}
}
public void shutdown() {
// take the 'batchStarted' state so offers and execution will not be triggered elsewhere
if (batchStarted.compareAndSet(false, true)) {
// get the write lock so offers are synced with this (we don't really need to unlock as this
// is a one-shot deal to shutdown)
batchLock.writeLock().lock();
try {
// if we win the 'start' and once we have the lock we can now shut it down otherwise another
// thread will finish executing this batch
if (count.get() > 0) {
logger.warn(
"Requests still exist in queue but will not be executed due to RequestCollapser shutdown: "
+ count.get(),
new IllegalStateException());
/*
* In the event that there is a concurrency bug or thread scheduling prevents the timer from ticking we need to handle this so the Future.get() calls do not block.
*
* I haven't been able to reproduce this use case on-demand but when stressing a machine saw this occur briefly right after the JVM paused (logs stopped scrolling).
*
* This safety-net just prevents the CollapsedRequestFutureImpl.get() from waiting on the CountDownLatch until its max timeout.
*/
for (CollapsedRequest<ResponseType, RequestArgumentType> request : batchArgumentQueue) {
try {
((CollapsedRequestSubject<ResponseType, RequestArgumentType>) request)
.setExceptionIfResponseNotReceived(
new IllegalStateException("Requests not executed before shutdown."));
} catch (Exception e) {
logger.debug("Failed to setException on CollapsedRequestFutureImpl instances.", e);
}
/**
* https://github.com/Netflix/Hystrix/issues/78 Include more info when collapsed
* requests remain in queue
*/
logger.warn(
"Request still in queue but not be executed due to RequestCollapser shutdown. Argument => "
+ request.getArgument()
+ " Request Object => "
+ request,
new IllegalStateException());
}
}
} finally {
batchLock.writeLock().unlock();
}
}
}
