cl-dispatch is a Common Lisp wrapper around Grand Central Dispatch (aka libdispatch). It allows you to make lightweight queues and semaphores which allow the kernel to schedule your tasks across multiple cores.

It's not well documented yet, but the lisp API is in cffi.lisp, and there is also Apple's documentation of the C API.

The lisp functions look and behave like the block versions (EG, dispatch_sync) with lisp functions instead of blocks, but they are implemented using the function versions (EG, dispatch_sync_f), which means that certain functions (EG, dispatch_once) aren't available in our API.

NOTE: On at least CCL and SBCL, dispatching asynchronously (this includes dispatch-after, etc.) to any queue other than the main queue will likely result in a segfault after not too long. See CCL issue #911.