Completes the definition of a set of threads to be executed simultaneously.
threadBegin; // Thread 1--isolates y,z y = x'x; z = y'y; threadEnd; threadBegin; // Thread 2--isolates q,r q = r'r; r = q'q; threadEnd; threadStat n = m'm; // Thread 3--isolates n threadStat p = o'o; // Thread 4--isolates p threadJoin; // Joins threads 1-4 b = z + r + n'p; // y,z,q,r,n,p available again, // can be read and written
Note how threads 1-4 isolate the various symbols they assign to–no other thread references the written symbols at all. Once the threads are joined, however, the symbols are again available for use, and can be both read and assigned to.
Each thread in the set must adhere to the writer-must-isolate rule (see Multi-Threaded Programming in GAUSS) Because the threads in a set execute simultaneously, there is no way of knowing in one thread the current “state” of a symbol in another, and thus no way of safely or meaningfully accessing it.