1. A method of broadcasting shared variable directory (SVD) information in a parallel computer, the parallel computer comprising a plurality of threads of execution, the threads organized into tasks, the parallel computer further comprising memory partitioned to provide each thread with a private memory and a shared memory, the method comprising: detecting, by a runtime optimizer of the parallel computer, a change in SVD information within an SVD associated with a first thread; identifying, by the runtime optimizer, a plurality of threads requiring notification of the change in the SVD information; and in response to detecting the change in the SVD information, broadcasting, via a system-level messaging layer in a protocol stack of the parallel computer to each thread of the identified plurality of threads, a broadcast message header and update data indicating the change in the SVD information.