JVM_xxx functions specific to multi-tasking are optional.
An MTASK ready JDK may or may not find them in the supplied JVM. As a result,
the JDK must look up dynamically these functions and set up a default replacement
(mostly, throw an exception, or perform a default operations when applicable).

All parts of the JDK that may interact with these optional multi-tasking operation
use an interface table initialized on first use (at well defined location in the code).