<s>
In	O
computer	B-General_Concept
programming	I-General_Concept
,	O
unreachable	B-General_Concept
memory	I-General_Concept
is	O
a	O
block	B-General_Concept
of	O
dynamically	B-General_Concept
allocated	I-General_Concept
memory	I-General_Concept
where	O
the	O
program	B-Application
that	O
allocated	O
the	O
memory	O
no	O
longer	O
has	O
any	O
reachable	O
pointer	O
that	O
refers	O
to	O
it	O
.	O
</s>
<s>
Similarly	O
,	O
an	O
unreachable	B-General_Concept
object	I-General_Concept
is	O
a	O
dynamically	O
allocated	O
object	O
that	O
has	O
no	O
reachable	O
reference	O
to	O
it	O
.	O
</s>
<s>
Informally	O
,	O
unreachable	B-General_Concept
memory	I-General_Concept
is	O
dynamic	B-General_Concept
memory	I-General_Concept
that	O
the	O
program	B-Application
cannot	O
reach	O
directly	O
,	O
nor	O
get	O
to	O
by	O
starting	O
at	O
an	O
object	O
it	O
can	O
reach	O
directly	O
,	O
and	O
then	O
following	O
a	O
chain	O
of	O
pointer	O
references	O
.	O
</s>
<s>
In	O
dynamic	B-General_Concept
memory	I-General_Concept
allocation	I-General_Concept
implementations	O
that	O
employ	O
a	O
garbage	B-General_Concept
collector	I-General_Concept
,	O
objects	O
are	O
reclaimed	O
after	O
they	O
become	O
unreachable	B-General_Concept
.	O
</s>
<s>
The	O
garbage	B-General_Concept
collector	I-General_Concept
is	O
able	O
to	O
determine	O
if	O
an	O
object	O
is	O
reachable	O
;	O
any	O
object	O
that	O
is	O
determined	O
to	O
no	O
longer	O
be	O
reachable	O
can	O
be	O
deallocated	O
.	O
</s>
<s>
Many	O
programming	O
languages	O
(	O
for	O
example	O
,	O
Java	B-Language
,	O
C#	B-Application
,	O
D	B-Application
,	O
Dylan	B-Language
,	O
Julia	B-Application
)	O
use	O
automatic	B-General_Concept
garbage	I-General_Concept
collection	I-General_Concept
.	O
</s>
<s>
In	O
contrast	O
,	O
when	O
memory	O
becomes	O
unreachable	B-General_Concept
in	O
dynamic	B-General_Concept
memory	I-General_Concept
allocation	I-General_Concept
implementations	O
that	O
require	O
explicit	O
deallocation	B-General_Concept
,	O
the	O
memory	O
can	O
no	O
longer	O
be	O
explicitly	O
deallocated	O
.	O
</s>
<s>
Unreachable	B-General_Concept
memory	I-General_Concept
in	O
systems	O
that	O
use	O
manual	O
memory	B-General_Concept
management	I-General_Concept
results	O
in	O
a	O
memory	B-Error_Name
leak	I-Error_Name
.	O
</s>
<s>
Some	O
garbage	B-General_Concept
collectors	I-General_Concept
implement	O
weak	B-General_Concept
references	I-General_Concept
.	O
</s>
<s>
If	O
an	O
object	O
is	O
reachable	O
only	O
through	O
either	O
weak	B-General_Concept
references	I-General_Concept
or	O
chains	O
of	O
references	O
that	O
include	O
a	O
weak	B-General_Concept
reference	I-General_Concept
,	O
then	O
the	O
object	O
is	O
said	O
to	O
be	O
.	O
</s>
<s>
The	O
garbage	B-General_Concept
collector	I-General_Concept
can	O
treat	O
a	O
weakly	O
reachable	O
object	B-Application
graph	I-Application
as	O
unreachable	B-General_Concept
and	O
deallocate	O
it	O
.	O
</s>
<s>
(	O
Conversely	O
,	O
references	O
that	O
prevent	O
an	O
object	O
from	O
being	O
garbage	B-General_Concept
collected	I-General_Concept
are	O
called	O
strong	B-General_Concept
references	I-General_Concept
;	O
a	O
weakly	O
reachable	O
object	O
is	O
unreachable	B-General_Concept
by	O
any	O
chain	O
consisting	O
only	O
of	O
strong	B-General_Concept
references	I-General_Concept
.	O
)	O
</s>
<s>
Some	O
garbage-collected	O
object-oriented	B-Language
languages	I-Language
,	O
such	O
as	O
Java	B-Language
and	O
Python	B-Language
,	O
feature	O
weak	B-General_Concept
references	I-General_Concept
.	O
</s>
<s>
The	O
Java	B-Language
package	I-Language
java.lang.ref	O
supports	O
soft	O
,	O
weak	O
and	O
phantom	O
references	O
,	O
resulting	O
in	O
the	O
additional	O
object	O
reachability	O
states	O
softly	B-General_Concept
reachable	I-General_Concept
and	O
phantom	B-General_Concept
reachable	I-General_Concept
.	O
</s>
<s>
Unreachable	B-General_Concept
memory	I-General_Concept
(	O
in	O
languages	O
,	O
like	O
C	O
,	O
that	O
do	O
not	O
reclaim	O
)	O
is	O
often	O
associated	O
with	O
software	B-General_Concept
aging	I-General_Concept
.	O
</s>
