Concurrency and Software Transactional Memories Satnam Singh, Microsoft Faculty Summit 2005

Software engineering. Multi-core. Future computing architectures. Reconfigurable computing. Message passing multi-processor systems. Alternative computing devices. Concurrency and Parallelism

Concurrent Programming Threads: C++, Java, C# Rendezvous: Ada. Synchronous: Esterel, Lustre. Join patterns: Jocaml, C-Omega. Implicit parallelism: functional languages. Hardware: VHDL, Verilog.

Reconfigurable Systems

Code/Circuit Generation Esterel design void uart_device_driver () {..... } uart.c VHDL, Verilog -> hardware implementation C -> software implementation

Hardware/Software

Fighting back Formal analysis techniques: contract checking behavioral types deadlock avoidance Language level support for concurreny. Lock free programming: Lock-free data structures Software transactional memories

Transactional Memory atomic A.withdraw(3) B.deposit(3) end IDEA ! Herlihy/Moss ISCA 1993 Steal ideas from the database community. atomic does what it says on the tin. Directly supports what the programmer is trying to do: an atomic transaction against memory. “Write the simple sequential code, and wrap atomic around it”.

How does it work? Optimistic concurrency atomic atomic Execute without taking any locks. Each read and write in is logged to a thread-local transaction log. Writes go to the log only, not to memory. At the end, the transaction tries to commit to memory. Commit may fail; then transaction is re-run

Transactional Memory No races: no locks, so you can’t forget to take one No lock-induced deadlock, because no locks Error recovery trivial: an exception inside atomic aborts the transaction Simple code is scalable. Implementation in Haskell: orElse combinator

Summary Question reliance on asynchronous concurrent programming languages: digital design synchronous reactive systems Prepare for alternative computing architectures. Formal analysis. Software Transactional Memories.