io.grpc.ThreadLocalContextStorage Maven / Gradle / Ivy
/*
* Copyright 2016 The gRPC Authors
*
* 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.grpc;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
* A {@link ThreadLocal}-based context storage implementation. Used by default.
*/
final class ThreadLocalContextStorage extends Context.Storage {
private static final Logger log = Logger.getLogger(ThreadLocalContextStorage.class.getName());
/**
* Currently bound context.
*/
// VisibleForTesting
static final ThreadLocal localContext = new ThreadLocal<>();
@Override
public Context doAttach(Context toAttach) {
Context current = current();
localContext.set(toAttach);
return current;
}
@Override
public void detach(Context toDetach, Context toRestore) {
if (current() != toDetach) {
// Log a severe message instead of throwing an exception as the context to attach is assumed
// to be the correct one and the unbalanced state represents a coding mistake in a lower
// layer in the stack that cannot be recovered from here.
log.log(Level.SEVERE, "Context was not attached when detaching",
new Throwable().fillInStackTrace());
}
if (toRestore != Context.ROOT) {
localContext.set(toRestore);
} else {
// Avoid leaking our ClassLoader via ROOT if this Thread is reused across multiple
// ClassLoaders, as is common for Servlet Containers. The ThreadLocal is weakly referenced by
// the Thread, but its current value is strongly referenced and only lazily collected as new
// ThreadLocals are created.
//
// Use set(null) instead of remove() since remove() deletes the entry which is then re-created
// on the next get() (because of initialValue() handling). set(null) has same performance as
// set(toRestore).
localContext.set(null);
}
}
@Override
public Context current() {
Context current = localContext.get();
if (current == null) {
return Context.ROOT;
}
return current;
}
}