<s>
In	O
parallel	B-Operating_System
computing	I-Operating_System
,	O
a	O
barrier	O
is	O
a	O
type	O
of	O
synchronization	O
method	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
parallel	O
do	O
loop	O
in	O
Fortran	B-Application
with	O
OpenMP	B-Application
will	O
not	O
be	O
allowed	O
to	O
continue	O
on	O
any	O
thread	O
until	O
the	O
last	O
iteration	O
is	O
completed	O
.	O
</s>
<s>
In	O
message	B-Architecture
passing	I-Architecture
,	O
any	O
global	O
communication	O
(	O
such	O
as	O
reduction	O
or	O
scatter	O
)	O
may	O
imply	O
a	O
barrier	O
.	O
</s>
<s>
In	O
concurrent	B-Architecture
computing	I-Architecture
,	O
a	O
barrier	O
may	O
be	O
in	O
a	O
raised	O
or	O
lowered	O
state	O
.	O
</s>
