ServerImpl.java

/*
 * Copyright 2014 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.internal;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
import static io.grpc.Contexts.statusFromCancelled;
import static io.grpc.Status.DEADLINE_EXCEEDED;
import static io.grpc.internal.GrpcUtil.MESSAGE_ENCODING_KEY;
import static io.grpc.internal.GrpcUtil.TIMEOUT_KEY;
import static java.util.concurrent.TimeUnit.NANOSECONDS;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.MoreObjects;
import com.google.common.base.Preconditions;
import com.google.common.util.concurrent.ListenableFuture;
import com.google.common.util.concurrent.SettableFuture;
import io.grpc.Attributes;
import io.grpc.BinaryLog;
import io.grpc.CompressorRegistry;
import io.grpc.Context;
import io.grpc.Deadline;
import io.grpc.Decompressor;
import io.grpc.DecompressorRegistry;
import io.grpc.HandlerRegistry;
import io.grpc.InternalChannelz;
import io.grpc.InternalChannelz.ServerStats;
import io.grpc.InternalChannelz.SocketStats;
import io.grpc.InternalInstrumented;
import io.grpc.InternalLogId;
import io.grpc.InternalServerInterceptors;
import io.grpc.Metadata;
import io.grpc.ServerCall;
import io.grpc.ServerCallHandler;
import io.grpc.ServerInterceptor;
import io.grpc.ServerMethodDefinition;
import io.grpc.ServerServiceDefinition;
import io.grpc.ServerTransportFilter;
import io.grpc.Status;
import io.perfmark.Link;
import io.perfmark.PerfMark;
import io.perfmark.Tag;
import java.io.IOException;
import java.io.InputStream;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.annotation.concurrent.GuardedBy;

/**
 * Default implementation of {@link io.grpc.Server}, for creation by transports.
 *
 * <p>Expected usage (by a theoretical TCP transport):
 * <pre><code>public class TcpTransportServerFactory {
 *   public static Server newServer(Executor executor, HandlerRegistry registry,
 *       String configuration) {
 *     return new ServerImpl(executor, registry, new TcpTransportServer(configuration));
 *   }
 * }</code></pre>
 *
 * <p>Starting the server starts the underlying transport for servicing requests. Stopping the
 * server stops servicing new requests and waits for all connections to terminate.
 */
public final class ServerImpl extends io.grpc.Server implements InternalInstrumented<ServerStats> {
  private static final Logger log = Logger.getLogger(ServerImpl.class.getName());
  private static final ServerStreamListener NOOP_LISTENER = new NoopListener();

  private final InternalLogId logId;
  private final ObjectPool<? extends Executor> executorPool;
  /** Executor for application processing. Safe to read after {@link #start()}. */
  private Executor executor;
  private final HandlerRegistry registry;
  private final HandlerRegistry fallbackRegistry;
  private final List<ServerTransportFilter> transportFilters;
  // This is iterated on a per-call basis.  Use an array instead of a Collection to avoid iterator
  // creations.
  private final ServerInterceptor[] interceptors;
  private final long handshakeTimeoutMillis;
  @GuardedBy("lock") private boolean started;
  @GuardedBy("lock") private boolean shutdown;
  /** non-{@code null} if immediate shutdown has been requested. */
  @GuardedBy("lock") private Status shutdownNowStatus;
  /** {@code true} if ServerListenerImpl.serverShutdown() was called. */
  @GuardedBy("lock") private boolean serverShutdownCallbackInvoked;
  @GuardedBy("lock") private boolean terminated;
  /** Service encapsulating something similar to an accept() socket. */
  private final List<? extends InternalServer> transportServers;
  private final Object lock = new Object();
  private final CountDownLatch startComplete = new CountDownLatch(1);
  @GuardedBy("lock") private boolean transportServersTerminated;
  /** {@code transportServer} and services encapsulating something similar to a TCP connection. */
  @GuardedBy("lock") private final Set<ServerTransport> transports = new HashSet<>();
  @GuardedBy("lock") private int activeTransportServers;

  private final Context rootContext;

  private final DecompressorRegistry decompressorRegistry;
  private final CompressorRegistry compressorRegistry;
  private final BinaryLog binlog;

  private final InternalChannelz channelz;
  private final CallTracer serverCallTracer;
  private final Deadline.Ticker ticker;

  /**
   * Construct a server.
   *
   * @param builder builder with configuration for server
   * @param transportServers transport servers that will create new incoming transports
   * @param rootContext context that callbacks for new RPCs should be derived from
   */
  ServerImpl(
      AbstractServerImplBuilder<?> builder,
      List<? extends InternalServer> transportServers,
      Context rootContext) {
    this.executorPool = Preconditions.checkNotNull(builder.executorPool, "executorPool");
    this.registry = Preconditions.checkNotNull(builder.registryBuilder.build(), "registryBuilder");
    this.fallbackRegistry =
        Preconditions.checkNotNull(builder.fallbackRegistry, "fallbackRegistry");
    Preconditions.checkNotNull(transportServers, "transportServers");
    Preconditions.checkArgument(!transportServers.isEmpty(), "no servers provided");
    this.transportServers = Collections.unmodifiableList(new ArrayList<>(transportServers));
    this.logId =
        InternalLogId.allocate("Server", String.valueOf(getListenSocketsIgnoringLifecycle()));
    // Fork from the passed in context so that it does not propagate cancellation, it only
    // inherits values.
    this.rootContext = Preconditions.checkNotNull(rootContext, "rootContext").fork();
    this.decompressorRegistry = builder.decompressorRegistry;
    this.compressorRegistry = builder.compressorRegistry;
    this.transportFilters = Collections.unmodifiableList(
        new ArrayList<>(builder.transportFilters));
    this.interceptors =
        builder.interceptors.toArray(new ServerInterceptor[builder.interceptors.size()]);
    this.handshakeTimeoutMillis = builder.handshakeTimeoutMillis;
    this.binlog = builder.binlog;
    this.channelz = builder.channelz;
    this.serverCallTracer = builder.callTracerFactory.create();
    this.ticker = checkNotNull(builder.ticker, "ticker");

    channelz.addServer(this);
  }

  /**
   * Bind and start the server.
   *
   * @return {@code this} object
   * @throws IllegalStateException if already started
   * @throws IOException if unable to bind
   */
  @Override
  public ServerImpl start() throws IOException {
    synchronized (lock) {
      checkState(!started, "Already started");
      checkState(!shutdown, "Shutting down");
      executor = Preconditions.checkNotNull(executorPool.getObject(), "executor");
      started = true;
    }

    // Start and wait for any ports to actually be bound.
    ServerListenerImpl listener = new ServerListenerImpl();
    try {
      for (InternalServer ts : transportServers) {
        ts.start(listener);
        synchronized (lock) {
          activeTransportServers++;
        }
      }
    } finally {
      startComplete.countDown();
    }

    return this;
  }

  @Override
  public int getPort() {
    synchronized (lock) {
      checkState(started, "Not started");
      checkState(!terminated, "Already terminated");
      for (InternalServer ts : transportServers) {
        SocketAddress addr = ts.getListenSocketAddress();
        if (addr instanceof InetSocketAddress) {
          return ((InetSocketAddress) addr).getPort();
        }
      }
      return -1;
    }
  }

  @Override
  public List<SocketAddress> getListenSockets() {
    synchronized (lock) {
      checkState(started, "Not started");
      checkState(!terminated, "Already terminated");
      return getListenSocketsIgnoringLifecycle();
    }
  }

  private List<SocketAddress> getListenSocketsIgnoringLifecycle() {
    synchronized (lock) {
      List<SocketAddress> addrs = new ArrayList<>(transportServers.size());
      for (InternalServer ts : transportServers) {
        addrs.add(ts.getListenSocketAddress());
      }
      return Collections.unmodifiableList(addrs);
    }
  }

  @Override
  public List<ServerServiceDefinition> getServices() {
    List<ServerServiceDefinition> fallbackServices = fallbackRegistry.getServices();
    if (fallbackServices.isEmpty()) {
      return registry.getServices();
    } else {
      List<ServerServiceDefinition> registryServices = registry.getServices();
      int servicesCount = registryServices.size() + fallbackServices.size();
      List<ServerServiceDefinition> services =
          new ArrayList<>(servicesCount);
      services.addAll(registryServices);
      services.addAll(fallbackServices);
      return Collections.unmodifiableList(services);
    }
  }

  @Override
  public List<ServerServiceDefinition> getImmutableServices() {
    return registry.getServices();
  }

  @Override
  public List<ServerServiceDefinition> getMutableServices() {
    return Collections.unmodifiableList(fallbackRegistry.getServices());
  }

  /**
   * Initiates an orderly shutdown in which preexisting calls continue but new calls are rejected.
   */
  @Override
  public ServerImpl shutdown() {
    boolean shutdownTransportServers;
    synchronized (lock) {
      if (shutdown) {
        return this;
      }
      shutdown = true;
      shutdownTransportServers = started;
      if (!shutdownTransportServers) {
        transportServersTerminated = true;
        checkForTermination();
      }
    }
    if (shutdownTransportServers) {
      awaitStartComplete();
      for (InternalServer ts : transportServers) {
        ts.shutdown();
      }
    }
    return this;
  }

  private void awaitStartComplete() {
    boolean startCompleted = false;
    try {
      startCompleted = startComplete.await(30, TimeUnit.SECONDS);
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
    }
    if (!startCompleted) {
      log.log(Level.WARNING, "Server was not starting properly, resources may leak");
    }
  }

  @Override
  public ServerImpl shutdownNow() {
    shutdown();
    Collection<ServerTransport> transportsCopy;
    Status nowStatus = Status.UNAVAILABLE.withDescription("Server shutdownNow invoked");
    boolean savedServerShutdownCallbackInvoked;
    synchronized (lock) {
      // Short-circuiting not strictly necessary, but prevents transports from needing to handle
      // multiple shutdownNow invocations if shutdownNow is called multiple times.
      if (shutdownNowStatus != null) {
        return this;
      }
      shutdownNowStatus = nowStatus;
      transportsCopy = new ArrayList<>(transports);
      savedServerShutdownCallbackInvoked = serverShutdownCallbackInvoked;
    }
    // Short-circuiting not strictly necessary, but prevents transports from needing to handle
    // multiple shutdownNow invocations, between here and the serverShutdown callback.
    if (savedServerShutdownCallbackInvoked) {
      // Have to call shutdownNow, because serverShutdown callback only called shutdown, not
      // shutdownNow
      for (ServerTransport transport : transportsCopy) {
        transport.shutdownNow(nowStatus);
      }
    }
    return this;
  }

  @Override
  public boolean isShutdown() {
    synchronized (lock) {
      return shutdown;
    }
  }

  @Override
  public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
    synchronized (lock) {
      long timeoutNanos = unit.toNanos(timeout);
      long endTimeNanos = System.nanoTime() + timeoutNanos;
      while (!terminated && (timeoutNanos = endTimeNanos - System.nanoTime()) > 0) {
        NANOSECONDS.timedWait(lock, timeoutNanos);
      }
      return terminated;
    }
  }

  @Override
  public void awaitTermination() throws InterruptedException {
    synchronized (lock) {
      while (!terminated) {
        lock.wait();
      }
    }
  }

  @Override
  public boolean isTerminated() {
    synchronized (lock) {
      return terminated;
    }
  }

  /**
   * Remove transport service from accounting collection and notify of complete shutdown if
   * necessary.
   *
   * @param transport service to remove
   */
  private void transportClosed(ServerTransport transport) {
    synchronized (lock) {
      if (!transports.remove(transport)) {
        throw new AssertionError("Transport already removed");
      }
      channelz.removeServerSocket(ServerImpl.this, transport);
      checkForTermination();
    }
  }

  /** Notify of complete shutdown if necessary. */
  private void checkForTermination() {
    synchronized (lock) {
      if (shutdown && transports.isEmpty() && transportServersTerminated) {
        if (terminated) {
          throw new AssertionError("Server already terminated");
        }
        terminated = true;
        channelz.removeServer(this);
        if (executor != null) {
          executor = executorPool.returnObject(executor);
        }
        lock.notifyAll();
      }
    }
  }

  private final class ServerListenerImpl implements ServerListener {

    @Override
    public ServerTransportListener transportCreated(ServerTransport transport) {
      synchronized (lock) {
        transports.add(transport);
      }
      ServerTransportListenerImpl stli = new ServerTransportListenerImpl(transport);
      stli.init();
      return stli;
    }

    @Override
    public void serverShutdown() {
      ArrayList<ServerTransport> copiedTransports;
      Status shutdownNowStatusCopy;
      awaitStartComplete();
      synchronized (lock) {
        activeTransportServers--;
        if (activeTransportServers != 0) {
          return;
        }

        // transports collection can be modified during shutdown(), even if we hold the lock, due
        // to reentrancy.
        copiedTransports = new ArrayList<>(transports);
        shutdownNowStatusCopy = shutdownNowStatus;
        serverShutdownCallbackInvoked = true;
      }
      for (ServerTransport transport : copiedTransports) {
        if (shutdownNowStatusCopy == null) {
          transport.shutdown();
        } else {
          transport.shutdownNow(shutdownNowStatusCopy);
        }
      }
      synchronized (lock) {
        transportServersTerminated = true;
        checkForTermination();
      }
    }
  }

  private final class ServerTransportListenerImpl implements ServerTransportListener {
    private final ServerTransport transport;
    private Future<?> handshakeTimeoutFuture;
    private Attributes attributes;

    ServerTransportListenerImpl(ServerTransport transport) {
      this.transport = transport;
    }

    public void init() {
      class TransportShutdownNow implements Runnable {
        @Override public void run() {
          transport.shutdownNow(Status.CANCELLED.withDescription("Handshake timeout exceeded"));
        }
      }

      if (handshakeTimeoutMillis != Long.MAX_VALUE) {
        handshakeTimeoutFuture = transport.getScheduledExecutorService()
            .schedule(new TransportShutdownNow(), handshakeTimeoutMillis, TimeUnit.MILLISECONDS);
      } else {
        // Noop, to avoid triggering Thread creation in InProcessServer
        handshakeTimeoutFuture = new FutureTask<Void>(new Runnable() {
          @Override public void run() {}
        }, null);
      }
      channelz.addServerSocket(ServerImpl.this, transport);
    }

    @Override
    public Attributes transportReady(Attributes attributes) {
      handshakeTimeoutFuture.cancel(false);
      handshakeTimeoutFuture = null;

      for (ServerTransportFilter filter : transportFilters) {
        attributes = Preconditions.checkNotNull(filter.transportReady(attributes),
            "Filter %s returned null", filter);
      }
      this.attributes = attributes;
      return attributes;
    }

    @Override
    public void transportTerminated() {
      if (handshakeTimeoutFuture != null) {
        handshakeTimeoutFuture.cancel(false);
        handshakeTimeoutFuture = null;
      }
      for (ServerTransportFilter filter : transportFilters) {
        filter.transportTerminated(attributes);
      }
      transportClosed(transport);
    }


    @Override
    public void streamCreated(ServerStream stream, String methodName, Metadata headers) {
      Tag tag = PerfMark.createTag(methodName, stream.streamId());
      PerfMark.startTask("ServerTransportListener.streamCreated", tag);
      try {
        streamCreatedInternal(stream, methodName, headers, tag);
      } finally {
        PerfMark.stopTask("ServerTransportListener.streamCreated", tag);
      }
    }

    private void streamCreatedInternal(
        final ServerStream stream, final String methodName, final Metadata headers, final Tag tag) {

      if (headers.containsKey(MESSAGE_ENCODING_KEY)) {
        String encoding = headers.get(MESSAGE_ENCODING_KEY);
        Decompressor decompressor = decompressorRegistry.lookupDecompressor(encoding);
        if (decompressor == null) {
          stream.close(
              Status.UNIMPLEMENTED.withDescription(
                  String.format("Can't find decompressor for %s", encoding)),
              new Metadata());
          return;
        }
        stream.setDecompressor(decompressor);
      }

      final StatsTraceContext statsTraceCtx = Preconditions.checkNotNull(
          stream.statsTraceContext(), "statsTraceCtx not present from stream");

      final Context.CancellableContext context = createContext(headers, statsTraceCtx);
      final Executor wrappedExecutor;
      // This is a performance optimization that avoids the synchronization and queuing overhead
      // that comes with SerializingExecutor.
      if (executor == directExecutor()) {
        wrappedExecutor = new SerializeReentrantCallsDirectExecutor();
      } else {
        wrappedExecutor = new SerializingExecutor(executor);
      }

      final Link link = PerfMark.linkOut();

      final JumpToApplicationThreadServerStreamListener jumpListener
          = new JumpToApplicationThreadServerStreamListener(
          wrappedExecutor, executor, stream, context, tag);
      stream.setListener(jumpListener);
      // Run in wrappedExecutor so jumpListener.setListener() is called before any callbacks
      // are delivered, including any errors. Callbacks can still be triggered, but they will be
      // queued.

      final class StreamCreated extends ContextRunnable {
        StreamCreated() {
          super(context);
        }

        @Override
        public void runInContext() {
          PerfMark.startTask("ServerTransportListener$StreamCreated.startCall", tag);
          PerfMark.linkIn(link);
          try {
            runInternal();
          } finally {
            PerfMark.stopTask("ServerTransportListener$StreamCreated.startCall", tag);
          }
        }

        private void runInternal() {
          ServerStreamListener listener = NOOP_LISTENER;
          try {
            ServerMethodDefinition<?, ?> method = registry.lookupMethod(methodName);
            if (method == null) {
              method = fallbackRegistry.lookupMethod(methodName, stream.getAuthority());
            }
            if (method == null) {
              Status status = Status.UNIMPLEMENTED.withDescription(
                  "Method not found: " + methodName);
              // TODO(zhangkun83): this error may be recorded by the tracer, and if it's kept in
              // memory as a map whose key is the method name, this would allow a misbehaving
              // client to blow up the server in-memory stats storage by sending large number of
              // distinct unimplemented method
              // names. (https://github.com/grpc/grpc-java/issues/2285)
              stream.close(status, new Metadata());
              context.cancel(null);
              return;
            }
            listener = startCall(stream, methodName, method, headers, context, statsTraceCtx, tag);
          } catch (RuntimeException e) {
            stream.close(Status.fromThrowable(e), new Metadata());
            context.cancel(null);
            throw e;
          } catch (Error e) {
            stream.close(Status.fromThrowable(e), new Metadata());
            context.cancel(null);
            throw e;
          } finally {
            jumpListener.setListener(listener);
          }

          // An extremely short deadline may expire before stream.setListener(jumpListener).
          // This causes NPE as in issue: https://github.com/grpc/grpc-java/issues/6300
          // Delay of setting cancellationListener to context will fix the issue.
          final class ServerStreamCancellationListener implements Context.CancellationListener {
            @Override
            public void cancelled(Context context) {
              Status status = statusFromCancelled(context);
              if (DEADLINE_EXCEEDED.getCode().equals(status.getCode())) {
                // This should rarely get run, since the client will likely cancel the stream
                // before the timeout is reached.
                stream.cancel(status);
              }
            }
          }

          context.addListener(new ServerStreamCancellationListener(), directExecutor());
        }
      }

      wrappedExecutor.execute(new StreamCreated());
    }

    private Context.CancellableContext createContext(
        Metadata headers, StatsTraceContext statsTraceCtx) {
      Long timeoutNanos = headers.get(TIMEOUT_KEY);

      Context baseContext = statsTraceCtx.serverFilterContext(rootContext);

      if (timeoutNanos == null) {
        return baseContext.withCancellation();
      }

      Context.CancellableContext context =
          baseContext.withDeadline(
              Deadline.after(timeoutNanos, NANOSECONDS, ticker),
              transport.getScheduledExecutorService());

      return context;
    }

    /** Never returns {@code null}. */
    private <ReqT, RespT> ServerStreamListener startCall(ServerStream stream, String fullMethodName,
        ServerMethodDefinition<ReqT, RespT> methodDef, Metadata headers,
        Context.CancellableContext context, StatsTraceContext statsTraceCtx, Tag tag) {
      // TODO(ejona86): should we update fullMethodName to have the canonical path of the method?
      statsTraceCtx.serverCallStarted(
          new ServerCallInfoImpl<>(
              methodDef.getMethodDescriptor(), // notify with original method descriptor
              stream.getAttributes(),
              stream.getAuthority()));
      ServerCallHandler<ReqT, RespT> handler = methodDef.getServerCallHandler();
      for (ServerInterceptor interceptor : interceptors) {
        handler = InternalServerInterceptors.interceptCallHandler(interceptor, handler);
      }
      ServerMethodDefinition<ReqT, RespT> interceptedDef = methodDef.withServerCallHandler(handler);
      ServerMethodDefinition<?, ?> wMethodDef = binlog == null
          ? interceptedDef : binlog.wrapMethodDefinition(interceptedDef);
      return startWrappedCall(fullMethodName, wMethodDef, stream, headers, context, tag);
    }

    private <WReqT, WRespT> ServerStreamListener startWrappedCall(
        String fullMethodName,
        ServerMethodDefinition<WReqT, WRespT> methodDef,
        ServerStream stream,
        Metadata headers,
        Context.CancellableContext context,
        Tag tag) {

      ServerCallImpl<WReqT, WRespT> call = new ServerCallImpl<>(
          stream,
          methodDef.getMethodDescriptor(),
          headers,
          context,
          decompressorRegistry,
          compressorRegistry,
          serverCallTracer,
          tag);

      ServerCall.Listener<WReqT> listener =
          methodDef.getServerCallHandler().startCall(call, headers);
      if (listener == null) {
        throw new NullPointerException(
            "startCall() returned a null listener for method " + fullMethodName);
      }
      return call.newServerStreamListener(listener);
    }
  }

  @Override
  public InternalLogId getLogId() {
    return logId;
  }

  @Override
  public ListenableFuture<ServerStats> getStats() {
    ServerStats.Builder builder = new ServerStats.Builder();
    for (InternalServer ts : transportServers) {
      // TODO(carl-mastrangelo): remove the list and just add directly.
      InternalInstrumented<SocketStats> stats = ts.getListenSocketStats();
      if (stats != null ) {
        builder.addListenSockets(Collections.singletonList(stats));
      }
    }
    serverCallTracer.updateBuilder(builder);
    SettableFuture<ServerStats> ret = SettableFuture.create();
    ret.set(builder.build());
    return ret;
  }

  @Override
  public String toString() {
    return MoreObjects.toStringHelper(this)
        .add("logId", logId.getId())
        .add("transportServers", transportServers)
        .toString();
  }

  private static final class NoopListener implements ServerStreamListener {
    @Override
    public void messagesAvailable(MessageProducer producer) {
      InputStream message;
      while ((message = producer.next()) != null) {
        try {
          message.close();
        } catch (IOException e) {
          // Close any remaining messages
          while ((message = producer.next()) != null) {
            try {
              message.close();
            } catch (IOException ioException) {
              // just log additional exceptions as we are already going to throw
              log.log(Level.WARNING, "Exception closing stream", ioException);
            }
          }
          throw new RuntimeException(e);
        }
      }
    }

    @Override
    public void halfClosed() {}

    @Override
    public void closed(Status status) {}

    @Override
    public void onReady() {}
  }

  /**
   * Dispatches callbacks onto an application-provided executor and correctly propagates
   * exceptions.
   */
  @VisibleForTesting
  static final class JumpToApplicationThreadServerStreamListener implements ServerStreamListener {
    private final Executor callExecutor;
    private final Executor cancelExecutor;
    private final Context.CancellableContext context;
    private final ServerStream stream;
    private final Tag tag;
    // Only accessed from callExecutor.
    private ServerStreamListener listener;

    public JumpToApplicationThreadServerStreamListener(Executor executor,
        Executor cancelExecutor, ServerStream stream, Context.CancellableContext context, Tag tag) {
      this.callExecutor = executor;
      this.cancelExecutor = cancelExecutor;
      this.stream = stream;
      this.context = context;
      this.tag = tag;
    }

    /**
     * This call MUST be serialized on callExecutor to avoid races.
     */
    private ServerStreamListener getListener() {
      if (listener == null) {
        throw new IllegalStateException("listener unset");
      }
      return listener;
    }

    @VisibleForTesting
    void setListener(ServerStreamListener listener) {
      Preconditions.checkNotNull(listener, "listener must not be null");
      Preconditions.checkState(this.listener == null, "Listener already set");
      this.listener = listener;
    }

    /**
     * Like {@link ServerCall#close(Status, Metadata)}, but thread-safe for internal use.
     */
    private void internalClose() {
      // TODO(ejona86): this is not thread-safe :)
      stream.close(Status.UNKNOWN, new Metadata());
    }

    @Override
    public void messagesAvailable(final MessageProducer producer) {
      PerfMark.startTask("ServerStreamListener.messagesAvailable", tag);
      final Link link = PerfMark.linkOut();

      final class MessagesAvailable extends ContextRunnable {

        MessagesAvailable() {
          super(context);
        }

        @Override
        public void runInContext() {
          PerfMark.startTask("ServerCallListener(app).messagesAvailable", tag);
          PerfMark.linkIn(link);
          try {
            getListener().messagesAvailable(producer);
          } catch (RuntimeException e) {
            internalClose();
            throw e;
          } catch (Error e) {
            internalClose();
            throw e;
          } finally {
            PerfMark.stopTask("ServerCallListener(app).messagesAvailable", tag);
          }
        }
      }

      try {
        callExecutor.execute(new MessagesAvailable());
      } finally {
        PerfMark.stopTask("ServerStreamListener.messagesAvailable", tag);
      }
    }

    @Override
    public void halfClosed() {
      PerfMark.startTask("ServerStreamListener.halfClosed", tag);
      final Link link = PerfMark.linkOut();

      final class HalfClosed extends ContextRunnable {
        HalfClosed() {
          super(context);
        }

        @Override
        public void runInContext() {
          PerfMark.startTask("ServerCallListener(app).halfClosed", tag);
          PerfMark.linkIn(link);
          try {
            getListener().halfClosed();
          } catch (RuntimeException e) {
            internalClose();
            throw e;
          } catch (Error e) {
            internalClose();
            throw e;
          } finally {
            PerfMark.stopTask("ServerCallListener(app).halfClosed", tag);
          }
        }
      }

      try {
        callExecutor.execute(new HalfClosed());
      } finally {
        PerfMark.stopTask("ServerStreamListener.halfClosed", tag);
      }
    }

    @Override
    public void closed(final Status status) {
      PerfMark.startTask("ServerStreamListener.closed", tag);
      try {
        closedInternal(status);
      } finally {
        PerfMark.stopTask("ServerStreamListener.closed", tag);
      }
    }

    private void closedInternal(final Status status) {
      // For cancellations, promptly inform any users of the context that their work should be
      // aborted. Otherwise, we can wait until pending work is done.
      if (!status.isOk()) {
        // The callExecutor might be busy doing user work. To avoid waiting, use an executor that
        // is not serializing.
        cancelExecutor.execute(new ContextCloser(context, status.getCause()));
      }
      final Link link = PerfMark.linkOut();

      final class Closed extends ContextRunnable {
        Closed() {
          super(context);
        }

        @Override
        public void runInContext() {
          PerfMark.startTask("ServerCallListener(app).closed", tag);
          PerfMark.linkIn(link);
          try {
            getListener().closed(status);
          } finally {
            PerfMark.stopTask("ServerCallListener(app).closed", tag);
          }
        }
      }

      callExecutor.execute(new Closed());
    }

    @Override
    public void onReady() {
      PerfMark.startTask("ServerStreamListener.onReady", tag);
      final Link link = PerfMark.linkOut();
      final class OnReady extends ContextRunnable {
        OnReady() {
          super(context);
        }

        @Override
        public void runInContext() {
          PerfMark.startTask("ServerCallListener(app).onReady", tag);
          PerfMark.linkIn(link);
          try {
            getListener().onReady();
          } catch (RuntimeException e) {
            internalClose();
            throw e;
          } catch (Error e) {
            internalClose();
            throw e;
          } finally {
            PerfMark.stopTask("ServerCallListener(app).onReady", tag);
          }
        }
      }

      try {
        callExecutor.execute(new OnReady());
      } finally {
        PerfMark.stopTask("ServerStreamListener.onReady", tag);
      }
    }
  }

  @VisibleForTesting
  static final class ContextCloser implements Runnable {
    private final Context.CancellableContext context;
    private final Throwable cause;

    ContextCloser(Context.CancellableContext context, Throwable cause) {
      this.context = context;
      this.cause = cause;
    }

    @Override
    public void run() {
      context.cancel(cause);
    }
  }
}