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Concurrency and Software Transactional Memories

Concurrency and Software Transactional Memories. Satnam Singh, Microsoft. Faculty Summit 2005. Concurrency and Parallelism. Software engineering. Multi-core. Future computing architectures. Reconfigurable computing. Message passing multi-processor systems. Alternative computing devices.

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Concurrency and Software Transactional Memories

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

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

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

  4. Reconfigurable Systems

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

  6. Hardware/Software

  7. 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

  8. Transactional Memory IDEA! • 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”. atomic A.withdraw(3) B.deposit(3) end Herlihy/Moss ISCA 1993

  9. How does it work? • Execute <body> without taking any locks. • Each read and write in <body> 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 Optimistic concurrency atomic <body>

  10. 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

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

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