Parallel Computer Architecture

372 CHAPTER 5 Shared Memory Multiprocessors

5.19 Suppose we have a machine that supports full-empty bits on every word in hard-

ware. This particular machine allows for the following C code functions:

ST_Special (loc, val) writes val to data location loc and sets the full bit.

If the full bit was already set, a trap is signaled.

int LD_jSpecial (loc) waits until the data location's full bit is set, reads the

data, clears the full bit, and returns the data as the result.

Write a C function swap(ij) that uses these primitives to atomically swap the

contents of two locations

A[i]

and A[j]. You should allow high concurrency (if mul-

tiple processor ...