Cilk [Blumofe95] is a coarse-grain parallel programming model based C. It is a faithful extension of C for multithreading that uses asynchronous parallelism and an efficient work-stealing schedule. Cilk is currently limited for shared memory architecture although some efforts for distributed memory have been published [Nikhil95].
Despite its simplicity, Cilk provides several advantages as mentioned in [Kuszmaul07]: simple, small, can use the best serial code, can express cache-efficient code, efficient (productivity), good performance on one processor and portable.
However, it also suffers some limitations, such as no direct support for fine-grained parallelism, synchronization flexibility, group team and lack of support for other languages such as Fortran and Java.
One famous Cilk example is as follows:
| Original | Cilk version |
|---|
int fib(int n) {
if (n < 2) return n;
else {
int n1, n2;
n1 = fib(n-1);
n2 = fib(n-2);
return;
}
} |
cilk int fib(n) {
if (n < 2) return n;
else {
int n1, n2;
n1 = spawn fib(n-1);
n2 = spawn fib(n-2);
sync;
return (n1 + n2);
}
}
|
The question is that if this language is good enough for multicore processors ? According to
Charles Leisorson from MIT, the answer is yes. (See
Multithreaded programming in Cilk). But not for general case I presume. Multicore processor architecture tends to encourage fine grain parallelism instead of coarse grain.
References
[Blumofe95] Blumofe, R. D., Joerg, C. F., Kuszmaul, B. C., Leiserson, C. E., Randall, K. H., and Zhou, Y. 1995. Cilk: an efficient multithreaded runtime system. In Proceedings of the Fifth ACM SIGPLAN Symposium on Principles and Practice of Parallel Programming (Santa Barbara, California, United States, July 19 - 21, 1995). R. L. Wexelblat, Ed. PPOPP '95. ACM Press, New York, NY, 207-216.
[Nikhil95] Nikhil, R. S. 1995. Cid: A Parallel, "Shared-Memory" C for Distributed-Memory Machines. In Proceedings of the 7th international Workshop on Languages and Compilers For Parallel Computing (August 08 - 10, 1994). K. Pingali, U. Banerjee, D. Gelernter, A. Nicolau, and D. A. Padua, Eds. Lecture Notes In Computer Science, vol. 892. Springer-Verlag, London, 376-390.
[Kuszmaul07] Kuszmaul, B. C. 2007. Cilk provides the "best overall productivity" for high performance computing: (and won the HPC challenge award to prove it). In Proceedings of the Nineteenth Annual ACM Symposium on Parallel Algorithms and Architectures (San Diego, California, USA, June 09 - 11, 2007). SPAA '07. ACM Press, New York, NY, 299-300.
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