<s>
multiple	O
computing	O
threads	B-Operating_System
(	O
or	O
processes	B-Operating_System
)	O
on	O
a	O
computer	O
.	O
</s>
<s>
computing	O
threads	B-Operating_System
(	O
or	O
processes	B-Operating_System
)	O
.	O
</s>
<s>
The	O
method	B-Language
calls	I-Language
can	O
be	O
blocking	B-Operating_System
or	O
non-blocking	B-Operating_System
.	O
</s>
<s>
called	O
by	O
different	O
threads	B-Operating_System
.	O
</s>
<s>
that	O
allow	O
multiple	O
threads	B-Operating_System
to	O
reach	O
consensus	B-Operating_System
.	O
</s>
<s>
This	O
consensus	B-Operating_System
can	O
be	O
achieved	O
in	O
a	O
blocking	B-Operating_System
manner	O
by	O
using	O
locks	B-Operating_System
,	O
or	O
without	O
locks	B-Operating_System
,	O
in	O
which	O
case	O
it	O
is	O
non-blocking	B-Operating_System
.	O
</s>
<s>
threads	B-Operating_System
must	O
be	O
thought	O
of	O
as	O
being	O
completely	O
asynchronous	O
:	O
</s>
<s>
they	O
are	O
subject	O
to	O
operating	B-General_Concept
system	I-General_Concept
preemption	O
,	O
page	O
faults	O
,	O
</s>
<s>
various	O
elements	O
of	O
the	O
multiprocessor	B-Operating_System
architecture	O
all	O
influence	O
performance	O
.	O
</s>
<s>
A	O
key	O
measure	O
for	O
performance	O
is	O
scalability	O
,	O
captured	O
by	O
the	O
speedup	B-Operating_System
of	O
the	O
implementation	O
.	O
</s>
<s>
On	O
a	O
machine	O
with	O
P	O
processors	O
,	O
the	O
speedup	B-Operating_System
is	O
the	O
ratio	O
of	O
the	O
structures	O
execution	O
time	O
on	O
a	O
single	O
processor	O
to	O
its	O
execution	O
time	O
on	O
P	O
processors	O
.	O
</s>
<s>
speedup	B-Operating_System
of	O
P	O
when	O
using	O
P	O
processors	O
.	O
</s>
<s>
speedup	B-Operating_System
grows	O
with	O
P	O
are	O
called	O
scalable	O
.	O
</s>
<s>
more	O
refined	O
versions	O
of	O
it	O
such	O
as	O
Gustafson	B-Operating_System
's	I-Operating_System
law	I-Operating_System
.	O
</s>
<s>
in	O
which	O
locks	B-Operating_System
control	O
access	O
to	O
memory	O
.	O
</s>
