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/*
* Copyright 2013 Google Inc.
*
* 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.common.jimfs;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.base.Throwables;
import com.google.common.collect.Sets;
import java.io.Closeable;
import java.io.IOException;
import java.nio.file.ClosedFileSystemException;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Object that manages the open/closed state of a file system, ensuring that all open resources are
* closed when the file system is closed and that file system methods throw an exception when the
* file system has been closed.
*
* @author Colin Decker
*/
final class FileSystemState implements Closeable {
private final Set<Closeable> resources = Sets.newConcurrentHashSet();
private final Runnable onClose;
private final AtomicBoolean open = new AtomicBoolean(true);
/** Count of resources currently in the process of being registered. */
private final AtomicInteger registering = new AtomicInteger();
FileSystemState(Runnable onClose) {
this.onClose = checkNotNull(onClose);
}
/** Returns whether or not the file system is open. */
public boolean isOpen() {
return open.get();
}
/**
* Checks that the file system is open, throwing {@link ClosedFileSystemException} if it is not.
*/
public void checkOpen() {
if (!open.get()) {
throw new ClosedFileSystemException();
}
}
/**
* Registers the given resource to be closed when the file system is closed. Should be called when
* the resource is opened.
*/
public <C extends Closeable> C register(C resource) {
// Initial open check to avoid incrementing registering if we already know it's closed.
// This is to prevent any possibility of a weird pathalogical situation where the do/while
// loop in close() keeps looping as register() is called repeatedly from multiple threads.
checkOpen();
registering.incrementAndGet();
try {
// Need to check again after marking registration in progress to avoid a potential race.
// (close() could have run completely between the first checkOpen() and
// registering.incrementAndGet().)
checkOpen();
resources.add(resource);
return resource;
} finally {
registering.decrementAndGet();
}
}
/** Unregisters the given resource. Should be called when the resource is closed. */
public void unregister(Closeable resource) {
resources.remove(resource);
}
/**
* Closes the file system, runs the {@code onClose} callback and closes all registered resources.
*/
@Override
public void close() throws IOException {
if (open.compareAndSet(true, false)) {
onClose.run();
Throwable thrown = null;
do {
for (Closeable resource : resources) {
try {
resource.close();
} catch (Throwable e) {
if (thrown == null) {
thrown = e;
} else {
thrown.addSuppressed(e);
}
} finally {
// ensure the resource is removed even if it doesn't remove itself when closed
resources.remove(resource);
}
}
// It's possible for a thread registering a resource to register that resource after open
// has been set to false and even after we've looped through and closed all the resources.
// Since registering must be incremented *before* checking the state of open, however,
// when we reach this point in that situation either the register call is still in progress
// (registering > 0) or the new resource has been successfully added (resources not empty).
// In either case, we just need to repeat the loop until there are no more register calls
// in progress (no new calls can start and no resources left to close.
} while (registering.get() > 0 || !resources.isEmpty());
Throwables.propagateIfPossible(thrown, IOException.class);
}
}
}
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