core: rename prepareToLoseNetwork() to enterIdle() (#4179)

alts/src/main/java/io/grpc/alts/AltsChannelBuilder.java

@@ -250,8 +250,8 @@ public final class AltsChannelBuilder extends ForwardingChannelBuilder<AltsChann
     }
 
     @Override
-    public void prepareToLoseNetwork() {
-      delegate.prepareToLoseNetwork();
+    public void enterIdle() {
+      delegate.enterIdle();
     }
   }
 }

core/src/main/java/io/grpc/ManagedChannel.java

@@ -128,15 +128,15 @@ public abstract class ManagedChannel extends Channel {
    * continue. New RPCs on the channel will trigger creation of a new connection.
    *
    * <p>This is primarily intended for Android users when a device is transitioning from a cellular
-   * to a wifi connection. Initially the device will maintain both the cellular and wifi
-   * connections, but the OS also issues a notification that after a short time the cellular
-   * connection will be terminated. Apps may invoke this method to ensure that new RPCs are created
-   * using the wifi connection, rather than the soon-to-be-disconnected cellular network.
+   * to a wifi connection. The OS will issue a notification that a new network (wifi) has been made
+   * the default, but for approximately 30 seconds the device will maintain both the cellular
+   * and wifi connections. Apps may invoke this method to ensure that new RPCs are created using the
+   * new default wifi network, rather than the soon-to-be-disconnected cellular network.
    *
    * <p>No-op if not supported by implementation.
    *
    * @since 1.11.0
    */
   @ExperimentalApi("https://github.com/grpc/grpc-java/issues/4056")
-  public void prepareToLoseNetwork() {}
+  public void enterIdle() {}
 }

core/src/main/java/io/grpc/internal/ForwardingManagedChannel.java

@@ -83,7 +83,7 @@ abstract class ForwardingManagedChannel extends ManagedChannel {
   }
 
   @Override
-  public void prepareToLoseNetwork() {
-    delegate.prepareToLoseNetwork();
+  public void enterIdle() {
+    delegate.enterIdle();
   }
 }

core/src/main/java/io/grpc/internal/ManagedChannelImpl.java

@@ -396,7 +396,7 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
     logger.log(Level.FINE, "[{0}] Entering idle mode", getLogId());
     // nameResolver and loadBalancer are guaranteed to be non-null.  If any of them were null,
     // either the idleModeTimer ran twice without exiting the idle mode, or the task in shutdown()
-    // did not cancel idleModeTimer, or prepareToLoseNetwork() ran while shutdown or in idle, all of
+    // did not cancel idleModeTimer, or enterIdle() ran while shutdown or in idle, all of
     // which are bugs.
     shutdownNameResolverAndLoadBalancer(true);
     nameResolver = getNameResolver(target, nameResolverFactory, nameResolverParams);
@@ -865,7 +865,7 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
   }
 
   @Override
-  public void prepareToLoseNetwork() {
+  public void enterIdle() {
     class PrepareToLoseNetworkRunnable implements Runnable {
       @Override
       public void run() {

core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java

@@ -1854,18 +1854,18 @@ public class ManagedChannelImplTest {
   }
 
   @Test
-  public void prepareToLoseNetworkEntersIdle() {
+  public void enterIdleEntersIdle() {
     createChannel(new FakeNameResolverFactory.Builder(expectedUri).build(), NO_INTERCEPTOR);
     helper.updateBalancingState(READY, mockPicker);
     assertEquals(READY, channel.getState(false));
 
-    channel.prepareToLoseNetwork();
+    channel.enterIdle();
 
     assertEquals(IDLE, channel.getState(false));
   }
 
   @Test
-  public void prepareToLoseNetworkAfterIdleTimerIsNoOp() {
+  public void enterIdleAfterIdleTimerIsNoOp() {
     long idleTimeoutMillis = 2000L;
     createChannel(
         new FakeNameResolverFactory.Builder(expectedUri).build(),
@@ -1875,7 +1875,7 @@ public class ManagedChannelImplTest {
     timer.forwardNanos(TimeUnit.MILLISECONDS.toNanos(idleTimeoutMillis));
     assertEquals(IDLE, channel.getState(false));
 
-    channel.prepareToLoseNetwork();
+    channel.enterIdle();
 
     assertEquals(IDLE, channel.getState(false));
   }