Pubsub: "Uncaught exception in the SynchronizationContext" When using example code from the "Getting Started Guide"

[mannuscript]

Environment details

2. OS type and version: Mac-os 10.13.6
3. Java version: 1.8.0_131
4. google-cloud-java version(s): google-cloud-core:1.91.3
5. google-cloud-pubsub:1.99.0

Steps to reproduce

1. Use the example here to publish a message to Pubsub.
2. Build and Run.

Stack trace

Nov 14, 2019 12:04:06 PM io.grpc.internal.ManagedChannelImpl$1 uncaughtException
    SEVERE: [Channel<313>: (pubsub.googleapis.com:443)] Uncaught exception in the SynchronizationContext. Panic!
    java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask@1453b889 rejected from java.util.concurrent.ScheduledThreadPoolExecutor@6f1d6611[Terminated, pool size = 0, active threads = 0, queued tasks = 0, completed tasks = 0]
        at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2047)
        at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:823)
        at java.util.concurrent.ScheduledThreadPoolExecutor.delayedExecute(ScheduledThreadPoolExecutor.java:326)
        at java.util.concurrent.ScheduledThreadPoolExecutor.schedule(ScheduledThreadPoolExecutor.java:533)
        at java.util.concurrent.ScheduledThreadPoolExecutor.execute(ScheduledThreadPoolExecutor.java:622)
        at io.grpc.internal.DelayedClientTransport.reprocess(DelayedClientTransport.java:297)
        at io.grpc.internal.ManagedChannelImpl.updateSubchannelPicker(ManagedChannelImpl.java:802)
        at io.grpc.internal.ManagedChannelImpl.access$4300(ManagedChannelImpl.java:106)
        at io.grpc.internal.ManagedChannelImpl$LbHelperImpl$1UpdateBalancingState.run(ManagedChannelImpl.java:1115)
        at io.grpc.SynchronizationContext.drain(SynchronizationContext.java:95)
        at io.grpc.SynchronizationContext.execute(SynchronizationContext.java:127)
        at io.grpc.internal.InternalSubchannel$TransportListener.transportReady(InternalSubchannel.java:507)
        at io.grpc.netty.shaded.io.grpc.netty.ClientTransportLifecycleManager.notifyReady(ClientTransportLifecycleManager.java:43)
        at io.grpc.netty.shaded.io.grpc.netty.NettyClientHandler$FrameListener.onSettingsRead(NettyClientHandler.java:835)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.DefaultHttp2ConnectionDecoder$FrameReadListener.onSettingsRead(DefaultHttp2ConnectionDecoder.java:479)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.DefaultHttp2ConnectionDecoder$PrefaceFrameListener.onSettingsRead(DefaultHttp2ConnectionDecoder.java:697)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2InboundFrameLogger$1.onSettingsRead(Http2InboundFrameLogger.java:93)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.DefaultHttp2FrameReader.readSettingsFrame(DefaultHttp2FrameReader.java:542)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.DefaultHttp2FrameReader.processPayloadState(DefaultHttp2FrameReader.java:263)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.DefaultHttp2FrameReader.readFrame(DefaultHttp2FrameReader.java:160)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2InboundFrameLogger.readFrame(Http2InboundFrameLogger.java:41)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.DefaultHttp2ConnectionDecoder.decodeFrame(DefaultHttp2ConnectionDecoder.java:174)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler$FrameDecoder.decode(Http2ConnectionHandler.java:378)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler$PrefaceDecoder.decode(Http2ConnectionHandler.java:242)
        at io.grpc.netty.shaded.io.netty.handler.codec.http2.Http2ConnectionHandler.decode(Http2ConnectionHandler.java:438)
        at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:505)
        at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:444)
        at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:283)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
        at io.grpc.netty.shaded.io.netty.handler.ssl.SslHandler.unwrap(SslHandler.java:1475)
        at io.grpc.netty.shaded.io.netty.handler.ssl.SslHandler.decodeJdkCompatible(SslHandler.java:1224)
        at io.grpc.netty.shaded.io.netty.handler.ssl.SslHandler.decode(SslHandler.java:1271)
        at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.decodeRemovalReentryProtection(ByteToMessageDecoder.java:505)
        at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:444)
        at io.grpc.netty.shaded.io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:283)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:352)
        at io.grpc.netty.shaded.io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1421)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:374)
        at io.grpc.netty.shaded.io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:360)
        at io.grpc.netty.shaded.io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:930)
        at io.grpc.netty.shaded.io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:163)
        at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:697)
        at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:632)
        at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:549)
        at io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:511)
        at io.grpc.netty.shaded.io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:918)
        at io.grpc.netty.shaded.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
        at io.grpc.netty.shaded.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
        at java.lang.Thread.run(Thread.java:748)

Any additional information below

messageIdFuture.get(); Resolves the issue. I am creating a PR.