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// 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 static java.util.Objects.requireNonNull;
import com.google.common.base.Throwables;
import com.google.gerrit.entities.Project;
import com.google.gerrit.server.RequestCleanup;
import com.google.gerrit.server.git.ProjectRunnable;
import com.google.inject.Key;
import com.google.inject.Scope;
import com.google.inject.servlet.ServletScopes;
import java.util.concurrent.Callable;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledThreadPoolExecutor;
/**
* Base class for propagating request-scoped data between threads.
*
* <p>Request scopes are typically linked to a {@link ThreadLocal}, which is only available to the
* current thread. In order to allow background work involving RequestScoped data, the ThreadLocal
* data must be copied from the request thread to the new background thread.
*
* <p>Every type of RequestScope must provide an implementation of RequestScopePropagator. See
* {@link #wrap(Callable)} for details on the implementation, usage, and restrictions.
*
* @see ThreadLocalRequestScopePropagator
*/
public abstract class RequestScopePropagator {
private final Scope scope;
private final ThreadLocalRequestContext local;
protected RequestScopePropagator(Scope scope, ThreadLocalRequestContext local) {
this.scope = scope;
this.local = local;
}
/**
* Ensures that the current request state is available when the passed in Callable is invoked.
*
* <p>If needed wraps the passed in Callable in a new {@link Callable} that propagates the current
* request state when the returned Callable is invoked. The method must be called in a request
* scope and the returned Callable may only be invoked in a thread that is not already in a
* request scope or is in the same request scope. The returned Callable will inherit toString()
* from the passed in Callable. A {@link ScheduledThreadPoolExecutor} does not accept a Callable,
* so there is no ProjectCallable implementation. Implementations of this method must be
* consistent with Guice's {@link ServletScopes#continueRequest(Callable, java.util.Map)}.
*
* <p>There are some limitations:
*
* <ul>
* <li>Derived objects (i.e. anything marked created in a request scope) will not be
* transported.
* <li>State changes to the request scoped context after this method is called will not be seen
* in the continued thread.
* </ul>
*
* @param callable the Callable to wrap.
* @return a new Callable which will execute in the current request scope.
*/
@SuppressWarnings("javadoc") // See GuiceRequestScopePropagator#wrapImpl
public final <T> Callable<T> wrap(Callable<T> callable) {
final RequestContext callerContext = requireNonNull(local.getContext());
final Callable<T> wrapped = wrapImpl(context(callerContext, cleanup(callable)));
return new Callable<>() {
@Override
public T call() throws Exception {
if (callerContext == local.getContext()) {
return callable.call();
}
return wrapped.call();
}
@Override
public String toString() {
return callable.toString();
}
};
}
/**
* Wraps runnable in a new {@link Runnable} that propagates the current request state when the
* runnable is invoked. The method must be called in a request scope and the returned Runnable may
* only be invoked in a thread that is not already in a request scope. The returned Runnable will
* inherit toString() from the passed in Runnable. Furthermore, if the passed runnable is of type
* {@link ProjectRunnable}, the returned runnable will be of the same type with the methods
* delegated.
*
* <p>See {@link #wrap(Callable)} for details on implementation and usage.
*
* @param runnable the Runnable to wrap.
* @return a new Runnable which will execute in the current request scope.
*/
public final Runnable wrap(Runnable runnable) {
final Callable<Object> wrapped = wrap(Executors.callable(runnable));
if (runnable instanceof ProjectRunnable) {
return new ProjectRunnable() {
@Override
public void run() {
try {
wrapped.call();
} catch (Exception e) {
Throwables.throwIfUnchecked(e);
throw new RuntimeException(e); // Not possible.
}
}
@Override
public Project.NameKey getProjectNameKey() {
return ((ProjectRunnable) runnable).getProjectNameKey();
}
@Override
public String getRemoteName() {
return ((ProjectRunnable) runnable).getRemoteName();
}
@Override
public boolean hasCustomizedPrint() {
return ((ProjectRunnable) runnable).hasCustomizedPrint();
}
@Override
public String toString() {
return runnable.toString();
}
};
}
return new Runnable() {
@Override
public void run() {
try {
wrapped.call();
} catch (RuntimeException e) {
throw e;
} catch (Exception e) {
throw new RuntimeException(e); // Not possible.
}
}
@Override
public String toString() {
return runnable.toString();
}
};
}
/**
* Ensures that the current request state is available when the passed in Callable is invoked
*
* <p>See {@link #wrap(Callable)}
*/
protected abstract <T> Callable<T> wrapImpl(Callable<T> callable);
protected <T> Callable<T> context(RequestContext context, Callable<T> callable) {
return () -> {
RequestContext old = local.setContext(context);
try {
return callable.call();
} finally {
local.setContext(old);
}
};
}
protected <T> Callable<T> cleanup(Callable<T> callable) {
return () -> {
RequestCleanup cleanup =
scope.scope(Key.get(RequestCleanup.class), RequestCleanup::new).get();
try {
return callable.call();
} finally {
cleanup.run();
}
};
}
}
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