Dispatch framework

The libdispatch is the wrapper for Grand Central Dispatch (GCD), the concurrency library used across all Swift platforms to provide support for concurrent code execution in multicore processors. GCD uses a dispatch queue to achieve the goal of executing tasks in parallel.  Each queue is a block of code (task) that can be executed synchronously or asynchronously on the main thread or worker thread. Tasks submitted to dispatch queues are executed efficiently on a pool of threads managed by the system. Submitted tasks are executed serially by default, but several tasks can be configured to run concurrently when submitted to the dispatch queue.