<s>
In	O
software	B-General_Concept
engineering	I-General_Concept
,	O
software	B-General_Concept
aging	I-General_Concept
is	O
the	O
tendency	O
for	O
software	O
to	O
fail	B-Error_Name
or	O
cause	O
a	O
system	O
failure	O
after	O
running	O
continuously	O
for	O
a	O
certain	O
time	O
,	O
or	O
because	O
of	O
ongoing	O
changes	O
in	O
systems	O
surrounding	O
the	O
software	O
.	O
</s>
<s>
Software	B-General_Concept
aging	I-General_Concept
has	O
several	O
causes	O
,	O
including	O
the	O
inability	O
of	O
old	O
software	O
to	O
adapt	B-General_Concept
to	O
changing	O
needs	O
or	O
changing	O
technology	O
platforms	O
,	O
and	O
the	O
tendency	O
of	O
software	O
patches	O
to	O
introduce	O
further	O
errors	O
.	O
</s>
<s>
Rebooting	B-Device
or	O
reinstalling	B-Application
the	O
software	O
can	O
act	O
as	O
a	O
short-term	O
fix	O
.	O
</s>
<s>
A	O
proactive	O
fault	O
management	O
method	O
to	O
deal	O
with	O
the	O
software	B-General_Concept
aging	I-General_Concept
incident	O
is	O
software	O
rejuvenation	O
.	O
</s>
<s>
From	O
both	O
an	O
academic	O
and	O
industrial	O
point	O
of	O
view	O
,	O
the	O
software	B-General_Concept
aging	I-General_Concept
phenomenon	O
has	O
increased	O
.	O
</s>
<s>
Memory	O
bloating	O
and	O
leaking	B-Error_Name
,	O
along	O
with	O
data	O
corruption	O
and	O
unreleased	O
file-locks	B-Application
are	O
particular	O
causes	O
of	O
software	B-General_Concept
aging	I-General_Concept
.	O
</s>
<s>
Software	B-Error_Name
failures	I-Error_Name
are	O
a	O
more	O
likely	O
cause	O
of	O
unplanned	O
systems	O
outages	O
compared	O
to	O
hardware	O
failures	O
.	O
</s>
<s>
In	O
widely	O
used	O
and	O
specialized	O
software	O
,	O
a	O
common	O
action	O
to	O
clear	O
a	O
problem	O
is	O
rebooting	B-Device
because	O
aging	O
occurs	O
due	O
to	O
the	O
complexity	O
of	O
software	O
which	O
is	O
never	O
free	O
of	O
errors	O
.	O
</s>
<s>
It	O
is	O
almost	O
impossible	O
to	O
fully	O
verify	O
that	O
a	O
piece	O
of	O
software	O
is	O
bug-free	O
.	O
</s>
<s>
Even	O
high-profile	O
software	O
such	O
as	O
Windows	B-Application
and	O
macOS	B-Operating_System
must	O
receive	O
continual	O
updates	O
to	O
improve	O
performance	O
and	O
fix	O
bugs	B-Error_Name
.	O
</s>
<s>
Software	O
rejuvenation	O
works	O
by	O
removing	O
accumulated	O
error	O
conditions	O
and	O
freeing	O
up	O
system	O
resources	O
,	O
for	O
example	O
by	O
flushing	O
operating	B-General_Concept
system	I-General_Concept
kernel	O
tables	O
,	O
using	O
garbage	B-General_Concept
collection	I-General_Concept
,	O
reinitializing	O
internal	O
data	O
structures	O
,	O
and	O
perhaps	O
the	O
most	O
well	O
known	O
rejuvenation	O
method	O
is	O
to	O
reboot	B-Device
the	O
system	O
.	O
</s>
<s>
The	O
method	O
most	O
individuals	O
are	O
familiar	O
with	O
is	O
the	O
hardware	O
or	O
software	O
reboot	B-Device
.	O
</s>
<s>
A	O
more	O
technical	O
example	O
would	O
be	O
the	O
web	B-Application
server	I-Application
software	O
Apache	B-Application
's	O
rejuvenation	O
method	O
.	O
</s>
<s>
Apache	B-Application
implements	O
one	O
form	O
of	O
rejuvenation	O
by	O
killing	O
and	O
recreating	O
processes	O
after	O
serving	O
a	O
certain	O
number	O
of	O
requests	O
.	O
</s>
<s>
Another	O
technique	O
is	O
to	O
restart	O
virtual	B-Architecture
machines	I-Architecture
running	O
in	O
a	O
cloud	B-Architecture
computing	I-Architecture
environment	O
.	O
</s>
<s>
The	O
IEEE	O
International	O
Symposium	O
on	O
Software	O
Reliability	O
Engineering	O
(	O
ISSRE	O
)	O
hosted	O
the	O
5th	O
annual	O
International	O
Workshop	O
on	O
Software	B-General_Concept
Aging	I-General_Concept
and	O
Rejuvenation	O
(	O
)	O
in	O
2013	O
.	O
</s>
<s>
Some	O
programming	O
languages	O
,	O
like	O
C	B-Language
and	O
C++	B-Language
,	O
allow	O
the	O
programmer	O
to	O
allocate	O
heap	O
memory	O
.	O
</s>
<s>
Freeing	O
the	O
memory	O
is	O
necessary	O
because	O
some	O
operating	B-General_Concept
systems	I-General_Concept
(	O
OS	O
)	O
do	O
n't	O
perform	O
garbage	B-General_Concept
collection	I-General_Concept
when	O
a	O
process	B-Operating_System
finishes	O
.	O
</s>
<s>
In	O
low	O
memory	O
conditions	O
,	O
the	O
computer	O
usually	O
functions	O
slower	O
due	O
to	O
intense	O
swapping	B-Architecture
and	O
thrashing	B-General_Concept
.	O
</s>
<s>
If	O
the	O
computer	O
runs	O
out	O
of	O
both	O
memory	O
and	O
swap	O
space	O
,	O
the	O
OS	O
might	O
automatically	O
reboot	B-Device
—	O
or	O
even	O
worse	O
hang	O
.	O
</s>
<s>
Programs	O
written	O
in	O
programming	O
languages	O
that	O
use	O
a	O
garbage	B-General_Concept
collector	I-General_Concept
(	O
e.g.	O
</s>
<s>
Java	B-Language
)	O
are	O
not	O
prone	O
to	O
memory	B-Error_Name
leaks	I-Error_Name
.	O
</s>
<s>
Sometimes	O
critical	O
components	O
of	O
the	O
OS	O
itself	O
can	O
be	O
a	O
source	O
of	O
memory	B-Error_Name
leaks	I-Error_Name
.	O
</s>
<s>
In	O
Microsoft	B-Application
Windows	I-Application
,	O
for	O
example	O
,	O
the	O
memory	O
use	O
of	O
a	O
Windows	B-Protocol
Explorer	I-Protocol
plug-in	O
might	O
drain	O
the	O
available	O
memory	O
to	O
the	O
point	O
of	O
making	O
the	O
entire	O
computer	O
unusable	O
.	O
</s>
<s>
A	O
reboot	B-Device
might	O
be	O
needed	O
.	O
</s>
<s>
Garbage	B-General_Concept
collection	I-General_Concept
is	O
a	O
form	O
of	O
automatic	B-General_Concept
memory	I-General_Concept
management	I-General_Concept
whereby	O
the	O
system	O
automatically	O
recovers	O
unused	O
memory	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
.NET	B-Application
Framework	I-Application
manages	O
the	O
allocation	O
and	O
release	O
of	O
memory	O
for	O
software	O
running	O
under	O
it	O
.	O
</s>
<s>
.NET	B-Application
based	O
web	O
services	O
manage	O
several	O
logical	O
types	O
of	O
memory	O
such	O
as	O
stack	O
,	O
unmanaged	O
and	O
managed	O
heap	O
(	O
free	O
space	O
)	O
.	O
</s>
<s>
As	O
the	O
physical	O
memory	O
gets	O
full	O
,	O
the	O
OS	O
writes	O
rarely	O
used	O
parts	O
of	O
it	O
to	O
disk	O
,	O
so	O
that	O
it	O
can	O
reallocate	O
it	O
to	O
another	O
application	O
,	O
a	O
process	B-Operating_System
known	O
as	O
paging	B-Architecture
or	O
swapping	B-Architecture
.	O
</s>
<s>
If	O
several	O
applications	O
are	O
all	O
making	O
large	O
demands	O
,	O
the	O
OS	O
can	O
spend	O
much	O
of	O
its	O
time	O
merely	O
moving	O
data	O
between	O
main	O
memory	O
and	O
disk	O
,	O
a	O
process	B-Operating_System
known	O
as	O
disk	B-General_Concept
thrashing	I-General_Concept
.	O
</s>
<s>
Since	O
the	O
garbage	B-General_Concept
collector	I-General_Concept
has	O
to	O
examine	O
all	O
of	O
the	O
allocations	O
to	O
decide	O
which	O
are	O
in	O
use	O
,	O
it	O
may	O
exacerbate	O
this	O
thrashing	B-General_Concept
.	O
</s>
<s>
As	O
a	O
result	O
,	O
extensive	O
swapping	B-Architecture
can	O
lead	O
to	O
garbage	B-General_Concept
collection	I-General_Concept
cycles	O
extended	O
from	O
milliseconds	O
to	O
tens	O
of	O
seconds	O
.	O
</s>
