Threading and Synchronization

  

Figure 11: Multithreading modules and interfaces. Modules are shown as blocks divided by horizontal planes representing interfaces.

To maximize flexibility, Jupiter uses two levels of interfaces for threading and synchronization, shown in Figure 11. The high-level interfaces, called Thread and Monitor (plus the corresponding Sources), provide the full Java concurrency semantics. The low-level interfaces, called ThinThread, Mutex, and Condition, provide the minimal semantics required by Java. These low-level interfaces are referred to collectively as the ThinThreads interface, which provides a small subset of the POSIX threads semantics [17]. The high- and low-level interfaces are complimentary in several ways:

• ThinThreads encapsulates the thread library beneath Jupiter. Thread and Monitor encapsulate the threading needs of the Java program running on top of Jupiter.

• ThinThreads provides the minimal requirements to make implementing Java threads possible. Thread and Monitor provide the maximum support to make implementing Java threads simple.

• ThinThreads is designed so that the implementation code which connects to the underlying thread library can be trivial. Thread and Monitor are designed so that the client code which uses them to implement Java threads can be trivial.

Separating the Java concurrency semantics from the semantics of the underlying thread library makes threading and synchronization modules easier to implement and modify.