Answer: 

Intel Cilk Plus is not provided as a statically linked library, for the following reasons:

Most libraries operate locally. For example, an Intel(R) MKL FFT transforms an array. It is irrelevant how many copies of the FFT there are. Multiple copies and versions can coexist without difficulty. But some libraries control program-wide resources, such as memory and processors. For example, garbage collectors control memory allocation across a program. Analogously, Intel Cilk Plus controls scheduling of tasks across a program. To do their job effectively, each of these must be a singleton; that is, have a sole instance that can coordinate activities across the entire program. Allowing k instances of the Intel Cilk Plus scheduler in a single program would cause there to be k times as many software threads as hardware threads. The program would operate inefficiently, because the machine would be oversubscribed by a factor of k, causing more context switching, cache contention, and memory consumption. Furthermore, Intel Cilk Plus 's efficient support for nested parallelism would be negated when nested parallelism arose from nested invocations of distinct schedulers.

The most practical solution for creating a program-wide singleton is a dynamic shared library that contains the singleton. Of course if the schedulers could cooperate, we would not need a singleton. But that cooperation requires a centralized agent to communicate through; that is, a singleton!

Our decision to omit a statically linkable version of Intel Cilk Plus was strongly influenced by our OpenMP experience. Like Intel Cilk Plus, OpenMP also tries to schedule across a program. A static version of the OpenMP run-time was once provided, and it has been a constant source of problems arising from duplicate schedulers. We think it best not to repeat that history. As an indirect proof of the validity of these considerations, we could point to the fact that Microsoft Visual C++* only provides OpenMP support via dynamic libraries.

Categories: