Remote: gRPC load balancing. (Part 3)

Implement SharedConnectionFactory which applys rate limiting on top of one connection.

PiperOrigin-RevId: 358084865

Author: Googler

src/main/java/com/google/devtools/build/lib/remote/grpc/BUILD

@@ -18,6 +18,7 @@ java_library(
     deps = [
         "//src/main/java/com/google/devtools/build/lib/concurrent",
         "//third_party:guava",
+        "//third_party:jsr305",
         "//third_party:rxjava3",
         "//third_party/grpc:grpc-jar",
     ],

src/main/java/com/google/devtools/build/lib/remote/grpc/ConnectionPool.java

@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.remote.grpc;
 
+import io.reactivex.rxjava3.core.Single;
 import java.io.Closeable;
 import java.io.IOException;
 
@@ -24,6 +25,13 @@
  * <p>Connections must be closed with {@link Connection#close()} in order to be reused later.
  */
 public interface ConnectionPool extends ConnectionFactory, Closeable {
+  /**
+   * Reuses a {@link Connection} in the pool and will potentially create a new connection depends on
+   * implementation.
+   */
+  @Override
+  Single<? extends Connection> create();
+
   /** Closes the connection pool and closes all the underlying connections */
   @Override
   void close() throws IOException;

src/main/java/com/google/devtools/build/lib/remote/grpc/SharedConnectionFactory.java

@@ -0,0 +1,170 @@
+// Copyright 2021 The Bazel Authors. All rights reserved.
+//
+// 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.devtools.build.lib.remote.grpc;
+
+import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
+import io.grpc.CallOptions;
+import io.grpc.ClientCall;
+import io.grpc.MethodDescriptor;
+import io.reactivex.rxjava3.core.Single;
+import io.reactivex.rxjava3.disposables.Disposable;
+import io.reactivex.rxjava3.functions.Action;
+import io.reactivex.rxjava3.subjects.AsyncSubject;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.concurrent.locks.ReentrantLock;
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
+
+/**
+ * A {@link ConnectionPool} that creates one connection using provided {@link ConnectionFactory} and
+ * shares the connection upto {@code maxConcurrency}.
+ *
+ * <p>This is useful if underlying connection maintains a connection pool internally. (such as
+ * {@code Channel} in gRPC)
+ *
+ * <p>Connections must be closed with {@link Connection#close()} in order to be reused later.
+ */
+@ThreadSafe
+public class SharedConnectionFactory implements ConnectionPool {
+  private final TokenBucket<Integer> tokenBucket;
+  private final ConnectionFactory factory;
+
+  @Nullable
+  @GuardedBy("connectionLock")
+  private AsyncSubject<Connection> connectionAsyncSubject = null;
+
+  private final ReentrantLock connectionLock = new ReentrantLock();
+  private final AtomicReference<Disposable> connectionCreationDisposable =
+      new AtomicReference<>(null);
+
+  public SharedConnectionFactory(ConnectionFactory factory, int maxConcurrency) {
+    this.factory = factory;
+
+    List<Integer> initialTokens = new ArrayList<>(maxConcurrency);
+    for (int i = 0; i < maxConcurrency; ++i) {
+      initialTokens.add(i);
+    }
+    this.tokenBucket = new TokenBucket<>(initialTokens);
+  }
+
+  @Override
+  public void close() throws IOException {
+    tokenBucket.close();
+
+    Disposable d = connectionCreationDisposable.getAndSet(null);
+    if (d != null && !d.isDisposed()) {
+      d.dispose();
+    }
+
+    try {
+      connectionLock.lockInterruptibly();
+
+      if (connectionAsyncSubject != null) {
+        Connection connection = connectionAsyncSubject.getValue();
+        if (connection != null) {
+          connection.close();
+        }
+
+        if (!connectionAsyncSubject.hasComplete()) {
+          connectionAsyncSubject.onError(new IllegalStateException("closed"));
+        }
+      }
+    } catch (InterruptedException e) {
+      throw new IOException(e);
+    } finally {
+      connectionLock.unlock();
+    }
+  }
+
+  private AsyncSubject<Connection> createUnderlyingConnectionIfNot() throws InterruptedException {
+    connectionLock.lockInterruptibly();
+    try {
+      if (connectionAsyncSubject == null || connectionAsyncSubject.hasThrowable()) {
+        connectionAsyncSubject =
+            factory
+                .create()
+                .doOnSubscribe(connectionCreationDisposable::set)
+                .toObservable()
+                .subscribeWith(AsyncSubject.create());
+      }
+
+      return connectionAsyncSubject;
+    } finally {
+      connectionLock.unlock();
+    }
+  }
+
+  private Single<? extends Connection> acquireConnection() {
+    return Single.fromCallable(this::createUnderlyingConnectionIfNot)
+        .flatMap(Single::fromObservable);
+  }
+
+  /**
+   * Reuses the underlying {@link Connection} and wait for it to be released if is exceeding {@code
+   * maxConcurrency}.
+   */
+  @Override
+  public Single<SharedConnection> create() {
+    return tokenBucket
+        .acquireToken()
+        .flatMap(
+            token ->
+                acquireConnection()
+                    .doOnError(ignored -> tokenBucket.addToken(token))
+                    .doOnDispose(() -> tokenBucket.addToken(token))
+                    .map(
+                        conn ->
+                            new SharedConnection(
+                                conn, /* onClose= */ () -> tokenBucket.addToken(token))));
+  }
+
+  /** Returns current number of available connections. */
+  public int numAvailableConnections() {
+    return tokenBucket.size();
+  }
+
+  /** A {@link Connection} which wraps an underlying connection and is shared between consumers. */
+  public static class SharedConnection implements Connection {
+    private final Connection connection;
+    private final Action onClose;
+
+    public SharedConnection(Connection connection, Action onClose) {
+      this.connection = connection;
+      this.onClose = onClose;
+    }
+
+    @Override
+    public <ReqT, RespT> ClientCall<ReqT, RespT> call(
+        MethodDescriptor<ReqT, RespT> method, CallOptions options) {
+      return connection.call(method, options);
+    }
+
+    @Override
+    public void close() throws IOException {
+      try {
+        onClose.run();
+      } catch (Throwable t) {
+        throw new IOException(t);
+      }
+    }
+
+    /** Returns the underlying connection this shared connection built on */
+    public Connection getUnderlyingConnection() {
+      return connection;
+    }
+  }
+}