software.amazon.awssdk.utils.cache.NonBlocking Maven / Gradle / Ivy
/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file 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 software.amazon.awssdk.utils.cache;
import java.time.Duration;
import java.time.Instant;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.Semaphore;
import java.util.concurrent.SynchronousQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;
import software.amazon.awssdk.annotations.SdkProtectedApi;
import software.amazon.awssdk.annotations.SdkTestInternalApi;
import software.amazon.awssdk.utils.Logger;
import software.amazon.awssdk.utils.ThreadFactoryBuilder;
/**
* A {@link CachedSupplier.PrefetchStrategy} that will run a single thread in the background to update the value. A call to
* prefetch on this strategy will never return.
*
* Multiple calls to {@link #prefetch(Runnable)} will still only result in one background task performing the update.
*/
@SdkProtectedApi
public class NonBlocking implements CachedSupplier.PrefetchStrategy {
private static final Logger log = Logger.loggerFor(NonBlocking.class);
/**
* The maximum number of concurrent refreshes before we start logging warnings and skipping refreshes.
*/
private static final int MAX_CONCURRENT_REFRESHES = 100;
/**
* The semaphore around concurrent background refreshes, enforcing the {@link #MAX_CONCURRENT_REFRESHES}.
*/
private static final Semaphore CONCURRENT_REFRESH_LEASES = new Semaphore(MAX_CONCURRENT_REFRESHES);
/**
* Thread used to kick off refreshes during the prefetch window. This does not do the actual refreshing. That's left for
* the {@link #EXECUTOR}.
*/
private static final ScheduledThreadPoolExecutor SCHEDULER =
new ScheduledThreadPoolExecutor(1, new ThreadFactoryBuilder().threadNamePrefix("sdk-cache-scheduler")
.daemonThreads(true)
.build());
/**
* Threads used to do the actual work of refreshing the values (because the cached supplier might block, so we don't
* want the work to be done by a small thread pool). This executor is created as unbounded, but we start complaining and
* skipping refreshes when there are more than {@link #MAX_CONCURRENT_REFRESHES} running.
*/
private static final ThreadPoolExecutor EXECUTOR =
new ThreadPoolExecutor(1, Integer.MAX_VALUE,
60L, TimeUnit.SECONDS,
new SynchronousQueue<>(),
new ThreadFactoryBuilder().threadNamePrefix("sdk-cache")
.daemonThreads(true)
.build());
/**
* An incrementing number, used to uniquely identify an instance of NonBlocking in the {@link #asyncThreadName}.
*/
private static final AtomicLong INSTANCE_NUMBER = new AtomicLong(0);
/**
* Whether we are currently refreshing the supplier. This is used to make sure only one caller is blocking at a time.
*/
private final AtomicBoolean currentlyPrefetching = new AtomicBoolean(false);
/**
* Name of the thread refreshing the cache for this strategy.
*/
private final String asyncThreadName;
/**
* The refresh task currently scheduled for this non-blocking instance. We ensure that no more than one task is scheduled
* per instance.
*/
private final AtomicReference> refreshTask = new AtomicReference<>();
/**
* Whether this strategy has been shutdown (and should stop doing background refreshes)
*/
private volatile boolean shutdown = false;
/**
* The cached supplier using this non-blocking instance.
*/
private volatile CachedSupplier> cachedSupplier;
static {
// Ensure that cancelling a task actually removes it from the queue.
SCHEDULER.setRemoveOnCancelPolicy(true);
}
/**
* Create a non-blocking prefetch strategy that uses the provided value for the name of the background thread that will be
* performing the update.
*/
public NonBlocking(String asyncThreadName) {
this.asyncThreadName = asyncThreadName + "-" + INSTANCE_NUMBER.getAndIncrement();
}
@SdkTestInternalApi
static ThreadPoolExecutor executor() {
return EXECUTOR;
}
@SdkTestInternalApi
public boolean isTaskScheduled() {
ScheduledFuture> refreshTask = this.refreshTask.get();
if (refreshTask == null) {
return true;
}
return !refreshTask.isDone();
}
@Override
public void initializeCachedSupplier(CachedSupplier> cachedSupplier) {
this.cachedSupplier = cachedSupplier;
}
@Override
public void prefetch(Runnable valueUpdater) {
// Only run one async prefetch at a time.
if (currentlyPrefetching.compareAndSet(false, true)) {
tryRunBackgroundTask(valueUpdater, () -> currentlyPrefetching.set(false));
}
}
@Override
public RefreshResult fetch(Supplier> supplier) {
RefreshResult result = supplier.get();
schedulePrefetch(result);
return result;
}
private void schedulePrefetch(RefreshResult> result) {
if (shutdown || result.staleTime() == null || result.prefetchTime() == null) {
return;
}
Duration timeUntilPrefetch = Duration.between(Instant.now(), result.prefetchTime());
if (timeUntilPrefetch.isNegative() || timeUntilPrefetch.toDays() > 7) {
log.debug(() -> "Skipping background refresh because the prefetch time is in the past or too far in the future: " +
result.prefetchTime());
return;
}
Instant backgroundRefreshTime = result.prefetchTime().plusSeconds(1);
Duration timeUntilBackgroundRefresh = timeUntilPrefetch.plusSeconds(1);
log.debug(() -> "Scheduling refresh attempt for " + backgroundRefreshTime + " (in " +
timeUntilBackgroundRefresh.toMillis() + " ms)");
ScheduledFuture> scheduledTask = SCHEDULER.schedule(() -> {
runWithInstanceThreadName(() -> {
log.debug(() -> "Executing refresh attempt scheduled for " + backgroundRefreshTime);
// If the supplier has already been prefetched, this will just be a cache hit.
tryRunBackgroundTask(cachedSupplier::get);
});
}, timeUntilBackgroundRefresh.toMillis(), TimeUnit.MILLISECONDS);
updateTask(scheduledTask);
if (shutdown) {
updateTask(null);
}
}
@Override
public void close() {
shutdown = true;
updateTask(null);
}
public void updateTask(ScheduledFuture> newTask) {
ScheduledFuture> currentTask;
do {
currentTask = refreshTask.get();
if (currentTask != null && !currentTask.isDone()) {
currentTask.cancel(false);
}
} while (!refreshTask.compareAndSet(currentTask, newTask));
}
public void tryRunBackgroundTask(Runnable runnable) {
tryRunBackgroundTask(runnable, () -> {
});
}
public void tryRunBackgroundTask(Runnable runnable, Runnable runOnCompletion) {
if (!CONCURRENT_REFRESH_LEASES.tryAcquire()) {
log.warn(() -> "Skipping a background refresh task because there are too many other tasks running.");
runOnCompletion.run();
return;
}
try {
EXECUTOR.submit(() -> {
runWithInstanceThreadName(() -> {
try {
runnable.run();
} catch (Throwable t) {
log.warn(() -> "Exception occurred in AWS SDK background task.", t);
} finally {
CONCURRENT_REFRESH_LEASES.release();
runOnCompletion.run();
}
});
});
} catch (Throwable t) {
log.warn(() -> "Exception occurred when submitting AWS SDK background task.", t);
CONCURRENT_REFRESH_LEASES.release();
runOnCompletion.run();
}
}
public void runWithInstanceThreadName(Runnable runnable) {
String baseThreadName = Thread.currentThread().getName();
try {
Thread.currentThread().setName(baseThreadName + "-" + asyncThreadName);
runnable.run();
} finally {
Thread.currentThread().setName(baseThreadName);
}
}
}