Parallel Computer Architecture

9.6 Advanced Topics 735

n

Acquire

Write x Ownership change

Read x P

2

and P

3

have read page Read x

x earlier and are therefore

on P

1

's sharing list

Write x Ownership change

Release Invalidations

Invalidation

applied

Write x

Invalidation not

applied,

since

current owner

FIGURE 9.20 Invalidation of a more recent copy in a simple single writer proto-

col.

Processor P

2

takes ownership from P

1

and then P

3

from P

2

. But P^s release happens

after all this. At the release,

P<]

sends invalidations to both P

2

and P

3

. P

2

applies the invali-

dation even though its copy is more recent than P^s (since it doesn't know) while P

3

does

not apply the invalidatio