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/*
* Copyright 2023 Google LLC
*
* 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 com.google.cloud.alloydb;
import com.google.common.base.Throwables;
import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.ListeningScheduledExecutorService;
import com.google.errorprone.annotations.concurrent.GuardedBy;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.function.Supplier;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/** Handles periodic refresh operations for an instance. */
class Refresher {
private static final Logger logger = LoggerFactory.getLogger(Refresher.class);
private static final long DEFAULT_CONNECT_TIMEOUT_MS = 45000;
private final ListeningScheduledExecutorService executor;
private final Object connectionInfoGuard = new Object();
private final AsyncRateLimiter rateLimiter;
private final RefreshCalculator refreshCalculator;
private final Supplier> refreshOperation;
private final String name;
@GuardedBy("connectionInfoGuard")
private ListenableFuture current;
@GuardedBy("connectionInfoGuard")
private ListenableFuture next;
@GuardedBy("connectionInfoGuard")
private boolean refreshRunning;
@GuardedBy("connectionInfoGuard")
private Throwable currentRefreshFailure;
@GuardedBy("connectionInfoGuard")
private boolean closed;
@GuardedBy("connectionInfoGuard")
private boolean triggerNextRefresh = true;
Refresher(
String name,
ListeningScheduledExecutorService executor,
Supplier> refreshOperation,
AsyncRateLimiter rateLimiter) {
this(name, executor, new RefreshCalculator(), refreshOperation, rateLimiter, true);
}
/**
* Create a new refresher with a special RefreshCalculator
*
* @param name the name of what is being refreshed, for logging.
* @param executor the executor to schedule refresh tasks.
* @param refreshCalculator the refresh calculator to determine when to start the next refresh.
* @param refreshOperation The supplier that refreshes the data.
* @param rateLimiter The rate limiter.
* @param triggerNextRefresh The next refresh operation should be triggered.
*/
Refresher(
String name,
ListeningScheduledExecutorService executor,
RefreshCalculator refreshCalculator,
Supplier> refreshOperation,
AsyncRateLimiter rateLimiter,
boolean triggerNextRefresh) {
this.name = name;
this.executor = executor;
this.refreshCalculator = refreshCalculator;
this.refreshOperation = refreshOperation;
this.rateLimiter = rateLimiter;
this.triggerNextRefresh = triggerNextRefresh;
synchronized (connectionInfoGuard) {
forceRefresh();
this.current = this.next;
}
}
/**
* Returns the current data related to the instance from {@link #startRefreshAttempt()}. May block
* if no valid data is currently available. This method is called by an application thread when it
* is trying to create a new connection to the database. (It is not called by a
* ListeningScheduledExecutorService task.) So it is OK to block waiting for a future to complete.
*
* When no refresh attempt is in progress, this returns immediately. Otherwise, it waits up to
* timeoutMs milliseconds. If a refresh attempt succeeds, returns immediately at the end of that
* successful attempt. If no attempts succeed within the timeout, throws a RuntimeException with
* the exception from the last failed refresh attempt as the cause.
*/
ConnectionInfo getConnectionInfo(long timeoutMs) {
ListenableFuture f;
synchronized (connectionInfoGuard) {
if (closed) {
throw new IllegalStateException("Connection closed");
}
f = current;
}
try {
return f.get(timeoutMs, TimeUnit.MILLISECONDS);
} catch (TimeoutException e) {
synchronized (connectionInfoGuard) {
if (currentRefreshFailure != null) {
throw new RuntimeException(
String.format(
"Unable to get valid instance data within %d ms."
+ " Last refresh attempt failed:",
timeoutMs)
+ currentRefreshFailure.getMessage(),
currentRefreshFailure);
}
}
throw new RuntimeException(
String.format(
"Unable to get valid instance data within %d ms. No refresh has completed.",
timeoutMs),
e);
} catch (ExecutionException | InterruptedException ex) {
Throwable cause = ex.getCause();
Throwables.throwIfUnchecked(cause);
throw new RuntimeException(cause);
}
}
/**
* Attempts to force a new refresh of the instance data. May fail if called too frequently or if a
* new refresh is already in progress. If successful, other methods will block until refresh has
* been completed.
*/
void forceRefresh() {
synchronized (connectionInfoGuard) {
if (closed) {
throw new IllegalStateException("Connection closed");
}
// Don't force a refresh until the current refresh operation
// has produced a successful refresh.
if (refreshRunning) {
return;
}
if (next != null) {
next.cancel(false);
}
logger.debug(
String.format(
"[%s] Force Refresh: the next refresh operation was cancelled."
+ " Scheduling new refresh operation immediately.",
name));
next = this.startRefreshAttempt();
}
}
/** Force a new refresh of the instance data if the client certificate has expired. */
void refreshIfExpired() {
ConnectionInfo info = getConnectionInfo(DEFAULT_CONNECT_TIMEOUT_MS);
logger.debug(
String.format(
"[%s] Now = %s, Current client certificate expiration = %s",
name, Instant.now().toString(), info.getExpiration()));
if (Instant.now().isAfter(info.getExpiration())) {
logger.debug(
String.format(
"[%s] Client certificate has expired. Starting next refresh operation immediately.",
name));
forceRefresh();
}
}
/**
* Triggers an update of internal information obtained from the AlloyDB Admin API, returning a
* future that resolves once a valid T has been acquired. This sets up a chain of futures that
* will 1. Acquire a rate limiter. 2. Attempt to fetch instance data. 3. Schedule the next attempt
* to get instance data based on the success/failure of this attempt.
*/
private ListenableFuture startRefreshAttempt() {
// As soon as we begin submitting refresh attempts to the executor, mark a refresh
// as "in-progress" so that subsequent forceRefresh() calls balk until this one completes.
synchronized (connectionInfoGuard) {
refreshRunning = true;
}
logger.debug(String.format("[%s] Refresh Operation: Acquiring rate limiter permit.", name));
ListenableFuture delay = rateLimiter.acquireAsync(executor);
delay.addListener(
() ->
logger.debug(
String.format("[%s] Refresh Operation: Rate limiter permit acquired.", name)),
executor);
// Once rate limiter is done, attempt to getInstanceData.
ListenableFuture f =
Futures.whenAllComplete(delay).callAsync(refreshOperation::get, executor);
// Finally, reschedule refresh after getInstanceData is complete.
return Futures.whenAllComplete(f).callAsync(() -> handleRefreshResult(f), executor);
}
private ListenableFuture handleRefreshResult(
ListenableFuture connectionInfoFuture) {
try {
// This does not block, because it only gets called when connectionInfoFuture has completed.
// This will throw an exception if the refresh attempt has failed.
ConnectionInfo info = connectionInfoFuture.get();
logger.debug(
String.format(
"[%s] Refresh Operation: Completed refresh with new certificate expiration at %s.",
name, info.getExpiration().toString()));
long secondsToRefresh =
refreshCalculator.calculateSecondsUntilNextRefresh(Instant.now(), info.getExpiration());
synchronized (connectionInfoGuard) {
// Refresh completed successfully, reset forceRefreshRunning.
refreshRunning = false;
currentRefreshFailure = null;
current = Futures.immediateFuture(info);
// Now update nextInstanceData to perform a refresh after the
// scheduled delay
if (!closed && triggerNextRefresh) {
logger.debug(
String.format(
"[%s] Refresh Operation: Next operation scheduled at %s.",
name,
Instant.now()
.plus(secondsToRefresh, ChronoUnit.SECONDS)
.truncatedTo(ChronoUnit.SECONDS)
.toString()));
next =
Futures.scheduleAsync(
this::startRefreshAttempt, secondsToRefresh, TimeUnit.SECONDS, executor);
}
// Resolves to an T immediately
return current;
}
} catch (ExecutionException | InterruptedException e) {
// No refresh retry when the TerminalException is raised.
final Throwable cause = e.getCause();
if (cause instanceof TerminalException) {
logger.debug(String.format("[%s] Refresh Operation: Failed! No retry.", name), e);
throw (TerminalException) cause;
}
logger.debug(
String.format(
"[%s] Refresh Operation: Failed! Starting next refresh operation immediately.", name),
e);
synchronized (connectionInfoGuard) {
currentRefreshFailure = e;
if (!closed) {
next = this.startRefreshAttempt();
}
// Resolves after the next successful refresh attempt.
return next;
}
}
}
void close() {
synchronized (connectionInfoGuard) {
if (closed) {
return;
}
// Cancel any in-progress requests
if (!this.current.isDone()) {
this.current.cancel(true);
}
if (!this.next.isDone()) {
this.next.cancel(true);
}
this.current = Futures.immediateFailedFuture(new RuntimeException("Connection is closed."));
this.closed = true;
}
}
ListenableFuture getNext() {
synchronized (connectionInfoGuard) {
return this.next;
}
}
ListenableFuture getCurrent() {
synchronized (connectionInfoGuard) {
return this.current;
}
}
}