<s>
Asynchrony	B-Operating_System
,	O
in	O
computer	B-General_Concept
programming	I-General_Concept
,	O
refers	O
to	O
the	O
occurrence	O
of	O
events	O
independent	O
of	O
the	O
main	O
program	O
flow	O
and	O
ways	O
to	O
deal	O
with	O
such	O
events	O
.	O
</s>
<s>
These	O
may	O
be	O
"	O
outside	O
"	O
events	O
such	O
as	O
the	O
arrival	O
of	O
signals	B-General_Concept
,	O
or	O
actions	O
instigated	O
by	O
a	O
program	O
that	O
take	O
place	O
concurrently	B-Architecture
with	O
program	O
execution	O
,	O
without	O
the	O
program	O
blocking	B-General_Concept
to	O
wait	O
for	O
results	O
.	O
</s>
<s>
Asynchronous	B-Architecture
input/output	I-Architecture
is	O
an	O
example	O
of	O
the	O
latter	O
case	O
of	O
asynchrony	B-Operating_System
,	O
and	O
lets	O
programs	O
issue	O
commands	O
to	O
storage	O
or	O
network	B-Architecture
devices	O
that	O
service	O
these	O
requests	O
while	O
the	O
processor	B-General_Concept
continues	O
executing	O
the	O
program	O
.	O
</s>
<s>
Doing	O
so	O
provides	O
a	O
degree	O
of	O
parallelism	B-Operating_System
.	O
</s>
<s>
A	O
common	O
way	O
for	O
dealing	O
with	O
asynchrony	B-Operating_System
in	O
a	O
programming	B-Application
interface	I-Application
is	O
to	O
provide	O
subroutines	O
that	O
return	O
a	O
future	B-Operating_System
or	I-Operating_System
promise	I-Operating_System
that	O
represents	O
the	O
ongoing	O
operation	O
,	O
and	O
a	O
synchronizing	O
operation	O
that	O
blocks	O
until	O
the	O
future	B-Operating_System
or	I-Operating_System
promise	I-Operating_System
is	O
completed	O
.	O
</s>
<s>
Some	O
programming	O
languages	O
,	O
such	O
as	O
Cilk	B-Language
,	O
have	O
special	O
syntax	O
for	O
expressing	O
an	O
asynchronous	B-Device
procedure	I-Device
call	I-Device
.	O
</s>
<s>
Examples	O
of	O
asynchrony	B-Operating_System
include	O
the	O
following	O
:	O
</s>
<s>
Asynchronous	B-Device
procedure	I-Device
call	I-Device
,	O
a	O
method	O
to	O
run	O
a	O
procedure	O
concurrently	B-Architecture
,	O
a	O
lightweight	O
alternative	O
to	O
Threads	B-Operating_System
.	O
</s>
<s>
Ajax	B-General_Concept
is	O
a	O
set	O
of	O
client-side	B-Operating_System
web	O
technologies	O
used	O
by	O
the	O
client	O
to	O
create	O
asynchronous	B-Architecture
I/O	I-Architecture
web	B-Application
applications	I-Application
.	O
</s>
<s>
Asynchronous	B-Operating_System
method	I-Operating_System
dispatch	I-Operating_System
(	O
AMD	O
)	O
,	O
a	O
data	O
communication	O
method	O
used	O
when	O
there	O
is	O
a	O
need	O
for	O
the	O
server	O
side	O
to	O
handle	O
a	O
large	O
number	O
of	O
long	O
lasting	O
client	O
requests	O
.	O
</s>
<s>
Using	O
synchronous	O
method	O
dispatch	O
(	O
SMD	O
)	O
,	O
this	O
scenario	O
may	O
turn	O
the	O
server	O
into	O
an	O
unavailable	O
busy	O
state	O
resulting	O
in	O
a	O
connection	O
failure	O
response	O
caused	O
by	O
a	O
network	B-Architecture
connection	O
request	O
timeout	O
.	O
</s>
<s>
The	O
servicing	O
of	O
a	O
client	O
request	O
is	O
immediately	O
dispatched	O
to	O
an	O
available	O
thread	B-Operating_System
from	O
a	O
pool	B-Operating_System
of	I-Operating_System
threads	I-Operating_System
and	O
the	O
client	O
is	O
put	O
in	O
a	O
blocking	B-General_Concept
state	O
.	O
</s>
<s>
In	O
case	O
of	O
thread	B-Operating_System
starvation	O
,	O
clients	O
are	O
blocked	O
waiting	O
for	O
threads	B-Operating_System
to	O
become	O
available	O
.	O
</s>
