// Copyright (C) 2012 The Android Open Source Project
//
// 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.gerrit.server.util;
import com.google.inject.OutOfScopeException;
import com.google.inject.Scope;
import java.util.concurrent.Callable;
/**
* {@link RequestScopePropagator} implementation for request scopes based on
* a {@link ThreadLocal} context.
*
* @param <C> "context" type stored in the {@link ThreadLocal}.
*/
public abstract class ThreadLocalRequestScopePropagator<C>
extends RequestScopePropagator {
private final ThreadLocal<C> threadLocal;
protected ThreadLocalRequestScopePropagator(Scope scope,
ThreadLocal<C> threadLocal, ThreadLocalRequestContext local) {
super(scope, local);
this.threadLocal = threadLocal;
}
/**
* @see RequestScopePropagator#wrap(Callable)
*/
@Override
protected final <T> Callable<T> wrapImpl(final Callable<T> callable) {
final C ctx = continuingContext(requireContext());
return new Callable<T>() {
@Override
public T call() throws Exception {
if (threadLocal.get() != null) {
// This is consistent with the Guice ServletScopes.continueRequest()
// behavior.
throw new IllegalStateException("Cannot continue request, "
+ "thread already has request in progress. A new thread must "
+ "be used to propagate the request scope context.");
}
threadLocal.set(ctx);
try {
return callable.call();
} finally {
threadLocal.remove();
}
}
};
}
private C requireContext() {
C context = threadLocal.get();
if (context == null) {
throw new OutOfScopeException("Cannot access scoped object");
}
return context;
}
/**
* Returns a new context object based on the passed in context that has no
* request scoped objects initialized.
* <p>
* Note that some code paths expect request-scoped objects like
* {@code CurrentUser} to be constructible starting from just the context
* object returned by this method. For example, in the SSH scope, the context
* includes the {@code SshSession}, which is used by
* {@code SshCurrentUserProvider} to construct a new {@code CurrentUser} in
* the new thread.
*
* @param ctx the context to continue.
* @return a new context.
*/
protected abstract C continuingContext(C ctx);
}