1. UCoM Software Architecture http://ucom

2. Universal Communicator Research UCoM Programming Model The Problem  Multi-threaded code is difficult to write and debug. Our goal is to reduce subtle concurrency bugs and race conditions Our Approach  Program written in terms of tasks that are not pre- emptively scheduled, i.e., cooperative multi-tasking  No mutual exclusion work by programmer  Only one task active at any time

3. Universal Communicator Research What are Tasks in UCoM Sequence of operations possibly containing I/O operations (e.g., network receives) Whole address space is “locked” for the task until it relinquishes control: Piecewise Serial “Lock” released automatically when task performs I/O Programmer must validate state after “reacquiring” lock; similar to high-performance servers Like event-driven programming but without inconvenience of using continuation-passing style in C/C++/C#.

4. Universal Communicator Research Support for UCoM Tasks Threads needed to achieve task abstraction: Scheduler thread for controlling execution One or more threads per type of I/O: network, disk, UI, brick Pool of worker threads for programmer tasks; Win32 fibers would be better but not available in WinCE When I/O request (e.g., file read) occurs in a task: Event posted on relevant I/O thread; task scheduled out I/O completes: result posted on scheduler thread Worker thread resumed ultimately with result