fix: stop overriding default grpc executor

gax-grpc/src/main/java/com/google/api/gax/grpc/InstantiatingGrpcChannelProvider.java

@@ -135,6 +135,11 @@ private InstantiatingGrpcChannelProvider(Builder builder) {
             : builder.directPathServiceConfig;
   }
 
+  /**
+   * @deprecated If executor is not set, this channel provider will create channels with default
+   *     grpc executor.
+   */
+  @Deprecated
   @Override
   public boolean needsExecutor() {
     return executor == null;
@@ -212,9 +217,7 @@ public TransportChannelProvider withCredentials(Credentials credentials) {
 
   @Override
   public TransportChannel getTransportChannel() throws IOException {
-    if (needsExecutor()) {
-      throw new IllegalStateException("getTransportChannel() called when needsExecutor() is true");
-    } else if (needsHeaders()) {
+    if (needsHeaders()) {
       throw new IllegalStateException("getTransportChannel() called when needsHeaders() is true");
     } else if (needsEndpoint()) {
       throw new IllegalStateException("getTransportChannel() called when needsEndpoint() is true");

gax-grpc/src/test/java/com/google/api/gax/grpc/testing/LocalChannelProvider.java

@@ -74,6 +74,7 @@ public boolean shouldAutoClose() {
     return true;
   }
 
+  @Deprecated
   @Override
   public boolean needsExecutor() {
     return false;

gax-httpjson/src/main/java/com/google/api/gax/httpjson/InstantiatingHttpJsonChannelProvider.java

@@ -93,6 +93,11 @@ private InstantiatingHttpJsonChannelProvider(
     this.mtlsProvider = mtlsProvider;
   }
 
+  /**
+   * @deprecated If executor is not set, this channel provider will create channels with default
+   *     executor defined in {@link ManagedHttpJsonChannel}.
+   */
+  @Deprecated
   @Override
   public boolean needsExecutor() {
     return executor == null;
@@ -149,9 +154,7 @@ public String getTransportName() {
 
   @Override
   public TransportChannel getTransportChannel() throws IOException {
-    if (needsExecutor()) {
-      throw new IllegalStateException("getTransportChannel() called when needsExecutor() is true");
-    } else if (needsHeaders()) {
+    if (needsHeaders()) {
       throw new IllegalStateException("getTransportChannel() called when needsHeaders() is true");
     } else {
       try {

gax-httpjson/src/main/java/com/google/api/gax/httpjson/ManagedHttpJsonChannel.java

@@ -37,19 +37,23 @@
 import com.google.api.core.BetaApi;
 import com.google.api.core.SettableApiFuture;
 import com.google.api.gax.core.BackgroundResource;
+import com.google.api.gax.core.InstantiatingExecutorProvider;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import java.io.IOException;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.TimeUnit;
 import javax.annotation.Nullable;
 
 /** Implementation of HttpJsonChannel which can issue http-json calls. */
 @BetaApi
 public class ManagedHttpJsonChannel implements HttpJsonChannel, BackgroundResource {
   private static final JsonFactory JSON_FACTORY = GsonFactory.getDefaultInstance();
+  private static final ExecutorService DEFAULT_EXECUTOR =
+      InstantiatingExecutorProvider.newBuilder().build().getExecutor();
 
   private final Executor executor;
   private final String endpoint;
@@ -134,7 +138,9 @@ public boolean awaitTermination(long duration, TimeUnit unit) throws Interrupted
   public void close() {}
 
   public static Builder newBuilder() {
-    return new Builder().setHeaderEnhancers(new LinkedList<HttpJsonHeaderEnhancer>());
+    return new Builder()
+        .setHeaderEnhancers(new LinkedList<HttpJsonHeaderEnhancer>())
+        .setExecutor(DEFAULT_EXECUTOR);
   }
 
   public static class Builder {
@@ -147,7 +153,7 @@ public static class Builder {
     private Builder() {}
 
     public Builder setExecutor(Executor executor) {
-      this.executor = executor;
+      this.executor = Preconditions.checkNotNull(executor);
       return this;
     }
 
@@ -167,7 +173,6 @@ public Builder setHttpTransport(HttpTransport httpTransport) {
     }
 
     public ManagedHttpJsonChannel build() {
-      Preconditions.checkNotNull(executor);
       Preconditions.checkNotNull(endpoint);
       return new ManagedHttpJsonChannel(
           executor, endpoint, jsonFactory, headerEnhancers, httpTransport);

gax/src/main/java/com/google/api/gax/rpc/ClientContext.java

@@ -50,7 +50,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
-import java.util.concurrent.Executor;
 import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import javax.annotation.Nonnull;
@@ -73,6 +72,10 @@ public abstract class ClientContext {
    */
   public abstract List<BackgroundResource> getBackgroundResources();
 
+  /**
+   * Gets the executor to use for running scheduled API call logic (such as retries and long-running
+   * operations).
+   */
   public abstract ScheduledExecutorService getExecutor();
 
   @Nullable
@@ -163,8 +166,8 @@ static String getEndpoint(
   public static ClientContext create(StubSettings settings) throws IOException {
     ApiClock clock = settings.getClock();
 
-    ExecutorProvider executorProvider = settings.getExecutorProvider();
-    final ScheduledExecutorService executor = executorProvider.getExecutor();
+    ExecutorProvider backgroundExecutorProvider = settings.getBackgroundExecutorProvider();
+    final ScheduledExecutorService backgroundExecutor = backgroundExecutorProvider.getExecutor();
 
     Credentials credentials = settings.getCredentialsProvider().getCredentials();
 
@@ -177,8 +180,11 @@ public static ClientContext create(StubSettings settings) throws IOException {
     }
 
     TransportChannelProvider transportChannelProvider = settings.getTransportChannelProvider();
-    if (transportChannelProvider.needsExecutor()) {
-      transportChannelProvider = transportChannelProvider.withExecutor((Executor) executor);
+    // After needsExecutor and StubSettings#setExecutorProvider are deprecated, transport channel
+    // executor can only be set from TransportChannelProvider#withExecutor directly, and a provider
+    // will have a default executor if it needs one.
+    if (transportChannelProvider.needsExecutor() && settings.getExecutorProvider() != null) {
+      transportChannelProvider = transportChannelProvider.withExecutor(backgroundExecutor);
     }
     Map<String, String> headers = getHeadersFromSettings(settings);
     if (transportChannelProvider.needsHeaders()) {
@@ -216,7 +222,7 @@ public static ClientContext create(StubSettings settings) throws IOException {
         watchdogProvider = watchdogProvider.withClock(clock);
       }
       if (watchdogProvider.needsExecutor()) {
-        watchdogProvider = watchdogProvider.withExecutor(executor);
+        watchdogProvider = watchdogProvider.withExecutor(backgroundExecutor);
       }
       watchdog = watchdogProvider.getWatchdog();
     }
@@ -226,16 +232,16 @@ public static ClientContext create(StubSettings settings) throws IOException {
     if (transportChannelProvider.shouldAutoClose()) {
       backgroundResources.add(transportChannel);
     }
-    if (executorProvider.shouldAutoClose()) {
-      backgroundResources.add(new ExecutorAsBackgroundResource(executor));
+    if (backgroundExecutorProvider.shouldAutoClose()) {
+      backgroundResources.add(new ExecutorAsBackgroundResource(backgroundExecutor));
     }
     if (watchdogProvider != null && watchdogProvider.shouldAutoClose()) {
       backgroundResources.add(watchdog);
     }
 
     return newBuilder()
         .setBackgroundResources(backgroundResources.build())
-        .setExecutor(executor)
+        .setExecutor(backgroundExecutor)
         .setCredentials(credentials)
         .setTransportChannel(transportChannel)
         .setHeaders(ImmutableMap.copyOf(settings.getHeaderProvider().getHeaders()))
@@ -289,6 +295,10 @@ public abstract static class Builder {
 
     public abstract Builder setBackgroundResources(List<BackgroundResource> backgroundResources);
 
+    /**
+     * Sets the executor to use for running scheduled API call logic (such as retries and
+     * long-running operations).
+     */
     public abstract Builder setExecutor(ScheduledExecutorService value);
 
     public abstract Builder setCredentials(Credentials value);

gax/src/main/java/com/google/api/gax/rpc/ClientSettings.java

@@ -36,6 +36,7 @@
 import com.google.api.gax.core.ExecutorProvider;
 import com.google.common.base.MoreObjects;
 import java.io.IOException;
+import java.util.concurrent.Executor;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import org.threeten.bp.Duration;
@@ -63,10 +64,16 @@ public final StubSettings getStubSettings() {
     return stubSettings;
   }
 
+  /** @deprecated Please use {@link #getBackgroundExecutorProvider()} */
+  @Deprecated
   public final ExecutorProvider getExecutorProvider() {
     return stubSettings.getExecutorProvider();
   }
 
+  public final ExecutorProvider getBackgroundExecutorProvider() {
+    return stubSettings.getBackgroundExecutorProvider();
+  }
+
   public final TransportChannelProvider getTransportChannelProvider() {
     return stubSettings.getTransportChannelProvider();
   }
@@ -112,6 +119,7 @@ public final Duration getWatchdogCheckInterval() {
   public String toString() {
     return MoreObjects.toStringHelper(this)
         .add("executorProvider", getExecutorProvider())
+        .add("backgroundExecutorProvider", getBackgroundExecutorProvider())
         .add("transportChannelProvider", getTransportChannelProvider())
         .add("credentialsProvider", getCredentialsProvider())
         .add("headerProvider", getHeaderProvider())
@@ -159,9 +167,27 @@ protected StubSettings.Builder getStubSettings() {
      * call logic (such as retries and long-running operations), and also to pass to the transport
      * settings if an executor is needed for the transport and it doesn't have its own executor
      * provider.
+     *
+     * @deprecated Please use {@link #setBackgroundExecutorProvider(ExecutorProvider)} for setting
+     *     executor to use for running scheduled API call logic. To set executor for {@link
+     *     TransportChannelProvider}, please use {@link
+     *     TransportChannelProvider#withExecutor(Executor)} instead.
      */
+    @Deprecated
     public B setExecutorProvider(ExecutorProvider executorProvider) {
       stubSettings.setExecutorProvider(executorProvider);
+      stubSettings.setBackgroundExecutorProvider(executorProvider);
+      return self();
+    }
+
+    /**
+     * Sets the ExecutorProvider to use for getting the executor to use for running scheduled API
+     * call logic (such as retries and long-running operations). This will not set the executor in
+     * {@link TransportChannelProvider}. To set executor for {@link TransportChannelProvider},
+     * please use {@link TransportChannelProvider#withExecutor(Executor)}.
+     */
+    public B setBackgroundExecutorProvider(ExecutorProvider executorProvider) {
+      stubSettings.setBackgroundExecutorProvider(executorProvider);
       return self();
     }
 
@@ -238,11 +264,29 @@ public B setWatchdogCheckInterval(@Nullable Duration checkInterval) {
       return self();
     }
 
-    /** Gets the ExecutorProvider that was previously set on this Builder. */
+    /**
+     * Gets the ExecutorProvider that was previously set on this Builder. This ExecutorProvider is
+     * to use for running asynchronous API call logic (such as retries and long-running operations),
+     * and also to pass to the transport settings if an executor is needed for the transport and it
+     * doesn't have its own executor provider.
+     *
+     * @deprecated Please use {@link #getBackgroundExecutorProvider()} for getting the executor
+     *     provider that's used for running scheduled API call logic.
+     */
+    @Deprecated
     public ExecutorProvider getExecutorProvider() {
       return stubSettings.getExecutorProvider();
     }
 
+    /**
+     * Gets the ExecutorProvider that was previously set on this Builder. This ExecutorProvider is
+     * to use for running asynchronous API call logic (such as retries and long-running operations).
+     * This ExecutorProvider is not used to set the executor in {@link TransportChannelProvider}.
+     */
+    public ExecutorProvider getBackgroundExecutorProvider() {
+      return stubSettings.getBackgroundExecutorProvider();
+    }
+
     /** Gets the TransportProvider that was previously set on this Builder. */
     public TransportChannelProvider getTransportChannelProvider() {
       return stubSettings.getTransportChannelProvider();
@@ -303,6 +347,7 @@ protected static void applyToAllUnaryMethods(
     public String toString() {
       return MoreObjects.toStringHelper(this)
           .add("executorProvider", getExecutorProvider())
+          .add("backgroundExecutorProvider", getBackgroundExecutorProvider())
           .add("transportChannelProvider", getTransportChannelProvider())
           .add("credentialsProvider", getCredentialsProvider())
           .add("headerProvider", getHeaderProvider())