Cilk

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Cilk

• Chao Huang
• CS498LVK

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Introduction

• A multithreaded parallel programming language
• Effective for exploiting dynamic, asynchronous
  parallelism (Chess games)
• Developed by the Supercomputing Technologies
  Group under Prof. Charles E. Leiserson at MIT

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Cilk Keywords

• spawn indicates the procedure can operate in
  parallel with other code the scheduler decides
  whether to execute it on a new thread or not
• sync indicates that the current procedure cannot
  proceed until all previous spawned procedures
  have completed and returned
• C elision of a Cilk program is a valid C program

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Example (1)

• cilk int fib (int n)
• if (n lt 2) return n
• else
• int x, y
• x spawn fib (n-1)
• y spawn fib (n-2)
• sync
• return (xy)

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Cilk Keywords

• inlet identifies a function inside the procedure
  as an inlet
• An inlet is a C function internal to a Cilk
  procedure which handles the returned results of a
  spawned procedure call
• Allows more complex way of handling return value
  in the parents frame

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Example (2)

• cilk int fib (int n)
• int x 0
• inlet void sum (int result)
• x result
• return
• if (nlt2) return n
• else
• sum(spawn fib (n-1))
• sum(spawn fib (n-2))
• sync
• return (x)

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Example (3)

• cilk int fib (int n)
• int x 0
• if (nlt2) return n
• else
• / implicit inlets /
• x spawn fib (n-1)
• x spawn fib (n-2)
• sync
• return (x)

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Cilk Keywords

• abort indicates that other procedures that have
  been spawned off by the parent procedure can be
  safely aborted
• Useful in speculative work such as space
  searching

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Cilk Keywords

• cilk void baz(int n)
• cilk void foo(int n)
• inlet void bar()
• abort
• bar(spawn baz(17))
• spawn baz(28)
• sync

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Implementation

• Scheduling scheme work-stealing
• Ready procedures are put on a double-ended queue
• The processor restores suspended procedures from
  the end of the deque they have been stored
• Underloaded processors steal work from other
  processors queues at the other end of the deque

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Important Applications

• Parallel chess programs
• Cilkchess
• Socrates
• Parallel gomoku