Threading issues

P4Java is inherently thread-safe when used properly. The following best practices can help to ensure that users do not encounter thread-related problems:

  • P4Java’s IOptionsServer object is partially thread-safe. The only state preserved in the underlying implementation classes is the Helix Server client that is associated with the server, and the server’s authentication state.
  • You can have multiple threads working against a single IOptionsServer object simultaneously, but note that changing authentication state (login state, password, user name, and so on) or the client that is associated with the server can have unpredictable results on long-running commands that are still running against that server object. You should ensure that changing these attributes only happens when other commands are not in progress with the particular server object.
  • P4Java makes no guarantees about the order of commands sent to the Helix Server by your applications. You must ensure that any required ordering is enforced.
  • Using a large numbers of threads against a single IOptionsServer object can impose a heavy load on the JVM and the corresponding server. To control load, create your own logic for limiting thread usage. Be certain that your use of threads does not cause deadlock or blocking. Consider using a single IOptionsServer object for each thread.
  • P4Java offers a number of useful callbacks for things like logging, file helpers, progress monitoring, and so on. These callbacks are performed within a live thread context. Ensure that any callbacks that you register or use do not cause blocking or deadlocks.
  • To obtain the best resource and memory allocation strategies for your specific threading needs, experiment with JVM invocation parameters. Garbage collection and memory allocation strategies can make quite a difference in raw threading throughput and latency, but often indirectly and unpredictably.