io.helidon.config.FileSystemWatcher Maven / Gradle / Ivy
Show all versions of helidon-config Show documentation
/*
* Copyright (c) 2020 Oracle and/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.
* 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.helidon.config;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.Arrays;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.function.Consumer;
import java.util.logging.Level;
import java.util.logging.Logger;
import io.helidon.config.spi.ChangeEventType;
import io.helidon.config.spi.ChangeWatcher;
import static java.nio.file.StandardWatchEventKinds.ENTRY_CREATE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_DELETE;
import static java.nio.file.StandardWatchEventKinds.ENTRY_MODIFY;
import static java.nio.file.StandardWatchEventKinds.OVERFLOW;
/**
* This change watcher is backed by {@link WatchService} to fire a polling event with every change on monitored {@link Path}.
*
* When a parent directory of the {@code path} is not available, or becomes unavailable later, a new attempt to register {@code
* WatchService} is scheduled again and again until the directory finally exists and the registration is successful.
*
* This {@link io.helidon.config.spi.ChangeWatcher} might be initialized with a custom {@link ScheduledExecutorService executor}
* or the {@link Executors#newSingleThreadScheduledExecutor()} is used if none is explicitly configured.
*
* This watcher notifies with appropriate change event in the following cases:
*
* - The watched directory is gone
* - The watched directory appears
* - A file in the watched directory is deleted, created or modified
*
*
* A single file system watcher may be used to watch multiple targets. In such a case, if {@link #stop()} is invoked, it stops
* watching all of these targets.
*
* @see WatchService
*/
public final class FileSystemWatcher implements ChangeWatcher {
private static final Logger LOGGER = Logger.getLogger(FileSystemWatcher.class.getName());
/*
* Configurable options through builder.
*/
private final List watchServiceModifiers = new LinkedList<>();
private ScheduledExecutorService executor;
private final boolean defaultExecutor;
private final long initialDelay;
private final long delay;
private final TimeUnit timeUnit;
/*
* Runtime options.
*/
private final List runtimes = Collections.synchronizedList(new LinkedList<>());
private FileSystemWatcher(Builder builder) {
ScheduledExecutorService executor = builder.executor;
if (executor == null) {
this.executor = Executors.newSingleThreadScheduledExecutor(new ConfigThreadFactory("file-watch-polling"));
this.defaultExecutor = true;
} else {
this.executor = executor;
this.defaultExecutor = false;
}
this.watchServiceModifiers.addAll(builder.watchServiceModifiers);
this.initialDelay = builder.initialDelay;
this.delay = builder.delay;
this.timeUnit = builder.timeUnit;
}
/**
* Fluent API builder for {@link io.helidon.config.FileSystemWatcher}.
* @return a new builder instance
*/
public static Builder builder() {
return new Builder();
}
/**
* Create a new file watcher with default configuration.
*
* @return a new file watcher
*/
public static FileSystemWatcher create() {
return builder().build();
}
@Override
public synchronized void start(Path target, Consumer> listener) {
if (defaultExecutor && executor.isShutdown()) {
executor = Executors.newSingleThreadScheduledExecutor(new ConfigThreadFactory("file-watch-polling"));
}
if (executor.isShutdown()) {
throw new ConfigException("Cannot start a watcher for path " + target + ", as the executor service is shutdown");
}
Monitor monitor = new Monitor(
listener,
target,
watchServiceModifiers);
ScheduledFuture future = executor.scheduleWithFixedDelay(monitor, initialDelay, delay, timeUnit);
this.runtimes.add(new TargetRuntime(monitor, future));
}
@Override
public synchronized void stop() {
runtimes.forEach(TargetRuntime::stop);
if (defaultExecutor) {
ConfigUtils.shutdownExecutor(executor);
}
}
@Override
public Class type() {
return Path.class;
}
/**
* Add modifiers to be used when registering the {@link WatchService}.
* See {@link Path#register(WatchService, WatchEvent.Kind[],
* WatchEvent.Modifier...) Path.register}.
*
* @param modifiers the modifiers to add
*/
public void initWatchServiceModifiers(WatchEvent.Modifier... modifiers) {
watchServiceModifiers.addAll(Arrays.asList(modifiers));
}
private static final class TargetRuntime {
private final Monitor monitor;
private final ScheduledFuture future;
private TargetRuntime(Monitor monitor, ScheduledFuture future) {
this.monitor = monitor;
this.future = future;
}
public void stop() {
monitor.stop();
future.cancel(true);
}
}
private static final class Monitor implements Runnable {
private final WatchService watchService;
private final Consumer> listener;
private final Path target;
private final List watchServiceModifiers;
private final boolean watchingFile;
private final Path watchedDir;
/*
* Runtime handling
*/
// we have failed - retry registration on next trigger
private volatile boolean failed = true;
// maybe we were stopped, do not do anything (the scheduled future will be cancelled shortly)
private volatile boolean shouldStop = false;
// last file information
private volatile boolean fileExists;
private WatchKey watchKey;
private Monitor(Consumer> listener,
Path target,
List watchServiceModifiers) {
try {
this.watchService = FileSystems.getDefault().newWatchService();
} catch (IOException e) {
throw new ConfigException("Cannot obtain WatchService.", e);
}
this.listener = listener;
this.target = target;
this.watchServiceModifiers = watchServiceModifiers;
this.fileExists = Files.exists(target);
this.watchingFile = !Files.isDirectory(target);
this.watchedDir = watchingFile ? target.getParent() : target;
}
@SuppressWarnings("unchecked")
@Override
public void run() {
if (shouldStop) {
return;
}
if (failed) {
register();
}
if (failed) {
return;
}
// if we used `take`, we would block the thread forever. This way we can use the same thread to handle
// multiple targets
WatchKey key = watchService.poll();
if (null == key) {
return;
}
List> watchEvents = key.pollEvents();
if (watchEvents.isEmpty()) {
// something happened, cannot get details
key.cancel();
listener.accept(ChangeEvent.create(target, ChangeEventType.CHANGED));
failed = true;
return;
}
// we actually have some changes
for (WatchEvent watchEvent : watchEvents) {
WatchEvent event = (WatchEvent) watchEvent;
Path eventPath = event.context();
// as we watch on whole directory
// make sure this is the watched file (if only interested in a single file)
if (watchingFile && !target.endsWith(eventPath)) {
continue;
}
eventPath = watchedDir.resolve(eventPath);
WatchEvent.Kind kind = event.kind();
if (kind.equals(OVERFLOW)) {
LOGGER.finest("Overflow event on path: " + eventPath);
continue;
}
if (kind.equals(ENTRY_CREATE)) {
LOGGER.finest("Entry created. Path: " + eventPath);
listener.accept(ChangeEvent.create(eventPath, ChangeEventType.CREATED));
} else if (kind == ENTRY_DELETE) {
LOGGER.finest("Entry deleted. Path: " + eventPath);
listener.accept(ChangeEvent.create(eventPath, ChangeEventType.DELETED));
} else if (kind == ENTRY_MODIFY) {
LOGGER.finest("Entry changed. Path: " + eventPath);
listener.accept(ChangeEvent.create(eventPath, ChangeEventType.CHANGED));
}
}
if (!key.reset()) {
LOGGER.log(Level.FINE, () -> "Directory of '" + target + "' is no more valid to be watched.");
failed = true;
}
}
private void fire(Path target, ChangeEventType eventType) {
listener.accept(ChangeEvent.create(target, eventType));
}
private synchronized void register() {
if (shouldStop) {
failed = true;
return;
}
boolean oldFileExists = fileExists;
try {
Path cleanTarget = target(this.target);
Path watchedDirectory = Files.isDirectory(cleanTarget) ? cleanTarget : parentDir(cleanTarget);
WatchKey oldWatchKey = watchKey;
watchKey = watchedDirectory.register(watchService,
new WatchEvent.Kind[] {ENTRY_CREATE, ENTRY_MODIFY, ENTRY_DELETE},
watchServiceModifiers.toArray(new WatchEvent.Modifier[0]));
failed = false;
if (null != oldWatchKey) {
oldWatchKey.cancel();
}
} catch (IOException e) {
LOGGER.log(Level.FINEST, "Failed to register watch service", e);
this.failed = true;
}
// in either case, let's see if our target has changed
this.fileExists = Files.exists(target);
if (fileExists != oldFileExists) {
if (fileExists) {
fire(this.target, ChangeEventType.CREATED);
} else {
fire(this.target, ChangeEventType.DELETED);
}
}
}
private synchronized void stop() {
this.shouldStop = true;
if (null != watchKey) {
watchKey.cancel();
}
try {
watchService.close();
} catch (IOException e) {
LOGGER.log(Level.FINE, "Failed to close watch service", e);
}
}
private Path target(Path path) throws IOException {
Path target = path;
while (Files.isSymbolicLink(target)) {
target = target.toRealPath();
}
return target;
}
private Path parentDir(Path path) {
Path parent = path.getParent();
if (parent == null) {
throw new ConfigException(
String.format("Cannot find parent directory for '%s' to register watch service.", path));
}
return parent;
}
}
/**
* Fluent API builder for {@link FileSystemWatcher}.
*/
public static final class Builder implements io.helidon.common.Builder {
private final List watchServiceModifiers = new LinkedList<>();
private ScheduledExecutorService executor;
private long initialDelay = 1000;
private long delay = 100;
private TimeUnit timeUnit = TimeUnit.MILLISECONDS;
private Builder() {
}
@Override
public FileSystemWatcher build() {
return new FileSystemWatcher(this);
}
/**
* Update this builder from meta configuration.
*
* Currently these options are supported:
*
* - {@code initial-delay-millis} - delay between the time this watcher is started
* and the time the first check is triggered
* - {@code delay-millis} - how often do we check the watcher service for changes
*
* As the watcher is implemented as non-blocking, a single watcher can be used to watch multiple
* directories using the same thread.
*
* @param metaConfig configuration of file system watcher
* @return updated builder instance
*/
public Builder config(Config metaConfig) {
metaConfig.get("initial-delay-millis")
.asLong()
.ifPresent(initDelay -> initialDelay = timeUnit.convert(initDelay, TimeUnit.MILLISECONDS));
metaConfig.get("delay-millis")
.asLong()
.ifPresent(delayMillis -> delay = timeUnit.convert(delayMillis, TimeUnit.MILLISECONDS));
return this;
}
/**
* Executor to use for this watcher.
* The task is scheduled for regular execution and is only blocking a thread for the time needed
* to process changed files.
*
* @param executor executor service to use
* @return updated builder instance
*/
public Builder executor(ScheduledExecutorService executor) {
this.executor = executor;
return this;
}
/**
* Configure schedule of the file watcher.
*
* @param initialDelay initial delay before regular scheduling starts
* @param delay delay between schedules
* @param timeUnit time unit of the delays
* @return updated builer instance
*/
public Builder schedule(long initialDelay, long delay, TimeUnit timeUnit) {
this.initialDelay = initialDelay;
this.delay = delay;
this.timeUnit = timeUnit;
return this;
}
/**
* Add a modifier of the watch service.
* Currently only implementation specific modifier are available, such as
* {@code com.sun.nio.file.SensitivityWatchEventModifier}.
*
* @param modifier modifier to use
* @return updated builder instance
*/
public Builder addWatchServiceModifier(WatchEvent.Modifier modifier) {
this.watchServiceModifiers.add(modifier);
return this;
}
/**
* Set modifiers to use for the watch service.
* Currently only implementation specific modifier are available, such as
* {@code com.sun.nio.file.SensitivityWatchEventModifier}.
*
* @param modifiers modifiers to use (replacing current configuration)
* @return updated builder instance
*/
public Builder watchServiceModifiers(List modifiers) {
this.watchServiceModifiers.clear();
this.watchServiceModifiers.addAll(modifiers);
return this;
}
}
}