Parallel Computer Architecture

9.1 Relaxed Memory Consistency Models 691

Pi,

P

2

Pn

Lock(TaskQ)

newTask—»next = Head;

if (Head != NULL)

Head-»prev = newTask;

Head = newTask;

UnLock(TaskQ)

(a)

n

TOP:

while(flag2==0);

A = 1;

u = B

v = C

D = B * C

flag2 = 0

flagl = 1

goto TOP;

TOP:

while(flagl==0:

x = A;

Y = D;

B = 3;

C = D / B;

flagl = 0.

flag2 = 1,

goto TOP;

(b)

FIGURE 9.5 Use of synchronization operations to coordinate access to ordinary shared data

variables. The synchronization may be through the use of explicit lock, unlock, and barrier operations

or through the use of flag variables for point-to-point events.

i Read/write

Read/write



Sync

*

1 Read/write

1 Read/write ...