1 Cilk Chao Huang CS498LVK

2 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

3 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

4 Example (1) cilk int fib (int n) { if (n < 2) return n; else { int x, y; x = spawn fib (n-1); y = spawn fib (n-2); sync; return (x+y); }

5 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 parent’s frame

6 Example (2) cilk int fib (int n) { int x = 0; inlet void sum (int result) { x += result; return; } if (n<2) return n; else { sum(spawn fib (n-1)); sum(spawn fib (n-2)); sync; return (x); }

7 Example (3) cilk int fib (int n) { int x = 0; if (n<2) return n; else { /* implicit inlets */ x += spawn fib (n-1); x += spawn fib (n-2); sync; return (x); }

8 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

9 Cilk Keywords cilk void baz(int n); cilk void foo(int n) { inlet void bar() { abort; } bar(spawn baz(17)); spawn baz(28); sync; }

10 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

11 Important Applications Parallel chess programs  Cilkchess  *Socrates  Parallel gomoku