<s>
In	O
computing	O
,	O
a	O
process	B-Operating_System
is	O
an	O
instance	O
of	O
a	O
computer	O
program	O
that	O
is	O
being	O
executed	O
.	O
</s>
<s>
A	O
process	B-Operating_System
always	O
exists	O
in	O
exactly	O
one	O
process	B-Operating_System
state	I-Operating_System
.	O
</s>
<s>
A	O
process	B-Operating_System
that	O
is	O
blocked	O
is	O
one	O
that	O
is	O
waiting	O
for	O
some	O
event	O
,	O
such	O
as	O
a	O
resource	B-General_Concept
becoming	O
available	O
or	O
the	O
completion	O
of	O
an	O
I/O	B-General_Concept
operation	I-General_Concept
.	O
</s>
<s>
In	O
a	O
multitasking	B-Operating_System
computer	O
system	O
,	O
individual	O
tasks	O
,	O
or	O
threads	B-Operating_System
of	I-Operating_System
execution	I-Operating_System
,	O
must	O
share	O
the	O
resources	O
of	O
the	O
system	O
.	O
</s>
<s>
Shared	B-General_Concept
resources	I-General_Concept
include	O
:	O
the	O
CPU	O
,	O
network	O
and	O
network	O
interfaces	O
,	O
memory	O
and	O
disk	O
.	O
</s>
<s>
When	O
one	O
task	B-General_Concept
is	O
using	O
a	O
resource	B-General_Concept
,	O
it	O
is	O
generally	O
not	O
possible	O
,	O
or	O
desirable	O
,	O
for	O
another	O
task	B-General_Concept
to	O
access	O
it	O
.	O
</s>
<s>
The	O
techniques	O
of	O
mutual	B-Operating_System
exclusion	I-Operating_System
are	O
used	O
to	O
prevent	O
this	O
concurrent	O
use	O
.	O
</s>
<s>
When	O
the	O
other	O
task	B-General_Concept
is	O
blocked	O
,	O
it	O
is	O
unable	O
to	O
execute	O
until	O
the	O
first	O
task	B-General_Concept
has	O
finished	O
using	O
the	O
shared	B-General_Concept
resource	I-General_Concept
.	O
</s>
<s>
Programming	O
languages	O
and	O
scheduling	O
algorithms	O
are	O
designed	O
to	O
minimize	O
the	O
over-all	O
effect	O
blocking	B-Operating_System
.	O
</s>
<s>
A	O
process	B-Operating_System
that	O
blocks	O
may	O
prevent	O
local	O
work-tasks	O
from	O
progressing	O
.	O
</s>
<s>
In	O
this	O
case	O
"	O
blocking	B-Operating_System
"	O
often	O
is	O
seen	O
as	O
not	O
wanted	O
.	O
</s>
<s>
An	O
example	O
is	O
"	O
blocking	B-Operating_System
on	O
a	O
channel	B-Operating_System
"	O
where	O
passively	O
waiting	O
for	O
the	O
other	O
part	O
(	O
no	O
polling	O
or	O
spin	O
loop	O
)	O
is	O
part	O
of	O
the	O
semantics	O
of	O
channels	O
.	O
</s>
<s>
Deadlock	B-Operating_System
means	O
that	O
processes	O
pathologically	O
wait	O
for	O
each	O
other	O
in	O
a	O
circle	O
.	O
</s>
<s>
As	O
such	O
it	O
is	O
not	O
directly	O
associated	O
with	O
blocking	B-Operating_System
.	O
</s>
<s>
Once	O
the	O
event	O
occurs	O
for	O
which	O
the	O
process	B-Operating_System
is	O
waiting	O
(	O
"	O
is	O
blocked	O
on	O
"	O
)	O
,	O
the	O
process	B-Operating_System
is	O
advanced	O
from	O
blocked	O
state	O
to	O
an	O
imminent	O
one	O
,	O
such	O
as	O
runnable	O
.	O
</s>
