JITServer introduces new command line options. Most of them configure JITServer parameters, such as network timeout, or server's IP address. Such options begin with -XX:JITServer* and are processed in JITServerParseCommonOptions(). The values of most options are stored in the PersistentInfo after they are parsed.
Another important function is setupJITServerOptions(). Executed during VM startup, it disables unsupported optimizations and modifies some heuristics.
A client must send its command line options to the server. -Xjit options are used to enable/disable optimizations/tracing options, while other options specify compilation-relevant VM parameters. For instance, -Xgc specifies a Garbage Collection policy. Despite the server not performing any GC, not knowing the right policy can affect functional correctness of the compiled code.
Two functions - J9::Options::packOptions and J9::Options::unpackOptions are used for serializing and deserializing client options, respectively. All relevant options must be sent to the server, but if some option doesn't seem to be working you may want to try adding it to the server as well. If it starts working, then the above functions must be modified to handle the missing option. There are also a few options which are not sent because they are uncommon and difficult to serialize. Such options are set to NULL within packOptions.
Serialized options are sent to the server with each compilation request. This is done for every compilation, because option subsets may enable or disable options for a subset of methods.