Cooperative Task Management without Manual Stack Management or, Event-driven programming is Not the Opposite of Threaded Programming Atul Adya, Jon Howell, Marvin Theimer, William J. Bolosky, John R. Douceur Microsoft Research Presented by: Yujing He ( ) CS 533-April 24 th, 2006

Event-Driven Programming

Threads & Fibers ☆ Threads ♦ lightest unit of kernel scheduling; ♦ preemptively scheduled; ♦ a stack and a copy of the registers; ☆ Fibers ♦ implemented in user space; ♦ cooperatively scheduled; ♦ efficient context switching;

Definitions ☆ Task Management preemptive, serial, cooperative ☆ Stack Management manual (event-driven), automatic (procedure-oriented) ☆ I/O Management synchronous, asynchronous ☆ Conflict Management pessimistic, optimistic ☆ Data Partitioning might reduce resource conflict

Concepts Relations

Other Concepts ☆ Continuation ♦ bundles state indicating where the event left off working on the task; ♦ plus a reference to an event-handler that encodes what should be done when the requested I/O has completed. ☆ Stack Ripping ♦ functions along the path ripped into more parts because of I/O calls; ♦ primary drawback to manual stack management in event- driven programming

Hybrid Approach ☆ Based on Windows Operating System ♦ Threads are scheduled preemptively; Fibers are scheduled cooperatively; ♦ Scheduling multiple fibers on a thread; Only one fiber is active at any time. ♦ Using adapter to connect between threaded programming and event programming; ☆ Examples ♦ Manual calling Automatic—Event calling Thread; ♦ Automatic calling Manual—Thread calling Event;

Hybrid Approach (Continued) ☆ Function Names GetCertData—Looks up certificate in the memory catch or disk/network and returns the answer; (manual) GetCAInfo—looks in a hash-table for a specified certificate authority (CA) id and returns a pointer to the corresponding object; (manual) VerifyCert—calls “GetCAInfo” to obtain a CA with which to verify a certificate; (automatic) FetchCert—fetches a security certificate using “GetCertData” and then calls “VerifyCert” in order to confirm its validity; (manual) FiberContinue—a continuation for event handlers; (manual) CFA—Continuation-to-Fiber Adapter (in Manual calling Automatic) FCA—Fiber-to-Continuation Adapter (in Automatic calling Manual)

Manual Calling Automatic FetchCert—fetches a security certificate using “GetCertData” and then calls “VerifyCert” in order to confirm its validity;

Automatic Calling Manual FetchCert—fetches a security certificate using “GetCertData” and then calls “VerifyCert” in order to confirm its validity;

Automatic Calling Manual Short Circuit Branch No I/O Block

Implementation ☆ Farsite: a distributed, secure, serverless file system running over desktops; (Windows NT) ☆ UCoM: a wireless phone application for hand-held devices such as PDAs. (Windows CE)

Conclusion ☆ Task management is best done cooperatively, and stack management is best done automatically ; ☆ A hybrid model adapts between code with automatic and with manual stack management, enabling cooperation among disparate programmers and software evolution of disparate code bases; ☆ The hybrid approach is in fact complicated, but it is also necessary sometimes.

References [1] Stephen Ferg; Event-Driven Programming: Introduction, Tutorial, history; [2] Atul Adya, Jon Howell, Marvin Theimer, et al. Cooperative Task Management without Manual Stack Management or, Event-driven Programming is Not the Opposite of Threaded Programming. Proceedings of the USENIX 2002 Annual Conference, pages , June [3] Wikipedia, the free encyclopedia; [4] Satish Gottimukkala; Presentation of Cooperative Task Management without Manual Stack Management or, Event-driven Programming is Not the Opposite of Threaded Programming;

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