<s>
In	O
software	B-General_Concept
engineering	I-General_Concept
,	O
a	O
circular	B-Language
dependency	I-Language
is	O
a	O
relation	O
between	O
two	O
or	O
more	O
modules	O
which	O
either	O
directly	O
or	O
indirectly	O
depend	O
on	O
each	O
other	O
to	O
function	O
properly	O
.	O
</s>
<s>
Such	O
modules	O
are	O
also	O
known	O
as	O
mutually	B-Algorithm
recursive	I-Algorithm
.	O
</s>
<s>
Circular	B-Language
dependencies	I-Language
are	O
natural	O
in	O
many	O
domain	B-Application
models	I-Application
where	O
certain	O
objects	O
of	O
the	O
same	O
domain	O
depend	O
on	O
each	O
other	O
.	O
</s>
<s>
However	O
,	O
in	O
software	O
design	O
,	O
circular	B-Language
dependencies	I-Language
between	O
larger	O
software	O
modules	O
are	O
considered	O
an	O
anti-pattern	O
because	O
of	O
their	O
negative	O
effects	O
.	O
</s>
<s>
Despite	O
this	O
,	O
such	O
circular	O
(	O
or	O
cyclic	O
)	O
dependencies	B-Application
have	O
been	O
found	O
to	O
be	O
widespread	O
among	O
the	O
source	O
files	O
of	O
real-world	O
software	O
.	O
</s>
<s>
Mutually	B-Algorithm
recursive	I-Algorithm
modules	O
are	O
,	O
however	O
,	O
somewhat	O
common	O
in	O
functional	B-Language
programming	I-Language
,	O
where	O
inductive	O
and	O
recursive	O
definitions	O
are	O
often	O
encouraged	O
.	O
</s>
<s>
Circular	B-Language
dependencies	I-Language
can	O
cause	O
many	O
unwanted	O
effects	O
in	O
software	O
programs	O
.	O
</s>
<s>
Most	O
problematic	O
from	O
a	O
software	O
design	O
point	O
of	O
view	O
is	O
the	O
tight	O
coupling	B-Application
of	O
the	O
mutually	O
dependent	O
modules	O
which	O
reduces	O
or	O
makes	O
impossible	O
the	O
separate	O
re-use	O
of	O
a	O
single	O
module	O
.	O
</s>
<s>
Circular	B-Language
dependencies	I-Language
can	O
cause	O
a	O
domino	O
effect	O
when	O
a	O
small	O
local	O
change	O
in	O
one	O
module	O
spreads	O
into	O
other	O
modules	O
and	O
has	O
unwanted	O
global	O
effects	O
(	O
program	O
errors	O
,	O
compile	O
errors	O
)	O
.	O
</s>
<s>
Circular	B-Language
dependencies	I-Language
can	O
also	O
result	O
in	O
infinite	O
recursions	O
or	O
other	O
unexpected	O
failures	O
.	O
</s>
<s>
Circular	B-Language
dependencies	I-Language
may	O
also	O
cause	O
memory	B-Error_Name
leaks	I-Error_Name
by	O
preventing	O
certain	O
very	O
primitive	O
automatic	O
garbage	B-General_Concept
collectors	I-General_Concept
(	O
those	O
that	O
use	O
reference	B-General_Concept
counting	I-General_Concept
)	O
from	O
deallocating	O
unused	O
objects	O
.	O
</s>
<s>
In	O
very	O
large	O
software	O
designs	O
,	O
software	B-General_Concept
engineers	I-General_Concept
may	O
lose	O
the	O
context	O
and	O
inadvertently	O
introduce	O
circular	B-Language
dependencies	I-Language
.	O
</s>
<s>
There	O
are	O
tools	O
to	O
analyze	O
software	O
and	O
find	O
unwanted	O
circular	B-Language
dependencies	I-Language
.	O
</s>
<s>
Circular	B-Language
dependencies	I-Language
can	O
be	O
introduced	O
when	O
implementing	O
callback	O
functionality	O
.	O
</s>
<s>
This	O
can	O
be	O
avoided	O
by	O
applying	O
design	O
patterns	O
like	O
the	O
observer	B-Language
pattern	I-Language
.	O
</s>
