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perf: WindowedLimit allow non-updating threads to proceed when updating #205

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merged 1 commit into from
Sep 12, 2024
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perf: WindowedLimit allow non-updating threads to proceed when updating #205

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31 changes: 21 additions & 10 deletions ...urrency-limits-core/src/main/java/com/netflix/concurrency/limits/limit/WindowedLimit.java
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantLock;
import java.util.function.Consumer;

public class WindowedLimit implements Limit {
Expand Down Expand Up @@ -103,7 +104,7 @@ public WindowedLimit build(Limit delegate) {

private final long minRttThreshold;

private final Object lock = new Object();
private final ReentrantLock lock = new ReentrantLock();

private final SampleWindowFactory sampleWindowFactory;

Expand All @@ -129,7 +130,7 @@ public void notifyOnChange(Consumer<Integer> consumer) {

@Override
public void onSample(long startTime, long rtt, int inflight, boolean didDrop) {
long endTime = startTime + rtt;
final long endTime = startTime + rtt;

if (rtt < minRttThreshold) {
return;
Expand All @@ -138,15 +139,25 @@ public void onSample(long startTime, long rtt, int inflight, boolean didDrop) {
sample.updateAndGet(current -> current.addSample(rtt, inflight, didDrop));

if (endTime > nextUpdateTime) {
synchronized (lock) {
// Double check under the lock
if (endTime > nextUpdateTime) {
SampleWindow current = sample.getAndSet(sampleWindowFactory.newInstance());
nextUpdateTime = endTime + Math.min(Math.max(current.getCandidateRttNanos() * 2, minWindowTime), maxWindowTime);

if (isWindowReady(current)) {
delegate.onSample(startTime, current.getTrackedRttNanos(), current.getMaxInFlight(), current.didDrop());
// Only allow one thread at propagate the sample to the delegate.
// Other threads are free to continue. They will continue to accumulate
// against 'sample'.
boolean haveLock = lock.tryLock();
if (haveLock) {
try {
// Double check under the lock, in case of the flow:
// A : check end time , lock , , set nextUpdateTime , unlock ,
// B : check end time , lock , [[nextUpdateTime has changed!]]
if (endTime > nextUpdateTime) {
SampleWindow current = sample.getAndSet(sampleWindowFactory.newInstance());
nextUpdateTime = endTime + Math.min(Math.max(current.getCandidateRttNanos() * 2, minWindowTime), maxWindowTime);

if (isWindowReady(current)) {
delegate.onSample(startTime, current.getTrackedRttNanos(), current.getMaxInFlight(), current.didDrop());
}
}
} finally {
lock.unlock();
}
}
}
Expand Down
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