I had a project with the latest datastore client (1.7.0) and added the pubsub client (0.25.0-beta).
When I tried to publish a message, it would not publish my message and hang forever with no error

after making some tests I found out those two clients had a conflict in their dependencies.
Datastore uses com.google.cloud.datastore:datastore-v1-protos:jar:1.3.0 that depends on com.google.protobuf:protobuf-java:jar:3.0.0 while PubSub uses com.google.cloud:google-cloud-core-grpc:jar:1.7.0 that depends on com.google.protobuf:protobuf-java:jar:3.3.1

I made it work excluding protobuf-java from the datastore dependency:

    <dependency>
        <groupId>com.google.cloud</groupId>
        <artifactId>google-cloud-datastore</artifactId>
        <version>1.7.0</version>
        <exclusions>
            <exclusion>
                <groupId>com.google.protobuf</groupId>
                <artifactId>protobuf-java</artifactId>
            </exclusion>
        </exclusions>
    </dependency>