<s>
Charm++	B-Language
is	O
a	O
parallel	O
object-oriented	B-Language
programming	I-Language
paradigm	O
based	O
on	O
C++	B-Language
and	O
developed	O
in	O
the	O
Parallel	B-Operating_System
Programming	I-Operating_System
Laboratory	O
at	O
the	O
University	O
of	O
Illinois	O
at	O
Urbana	O
–	O
Champaign	O
.	O
</s>
<s>
Charm++	B-Language
is	O
designed	O
with	O
the	O
goal	O
of	O
enhancing	O
programmer	O
productivity	O
by	O
providing	O
a	O
high-level	O
abstraction	O
of	O
a	O
parallel	B-Operating_System
program	I-Operating_System
while	O
at	O
the	O
same	O
time	O
delivering	O
good	O
performance	O
on	O
a	O
wide	O
variety	O
of	O
underlying	O
hardware	O
platforms	O
.	O
</s>
<s>
Programs	O
written	O
in	O
Charm++	B-Language
are	O
decomposed	O
into	O
a	O
number	O
of	O
cooperating	O
message-driven	O
objects	O
called	O
chares	O
.	O
</s>
<s>
When	O
a	O
programmer	O
invokes	O
a	O
method	O
on	O
an	O
object	O
,	O
the	O
Charm++	B-Language
runtime	O
system	O
sends	O
a	O
message	O
to	O
the	O
invoked	O
object	O
,	O
which	O
may	O
reside	O
on	O
the	O
local	O
processor	O
or	O
on	O
a	O
remote	O
processor	O
in	O
a	O
parallel	B-Operating_System
computation	I-Operating_System
.	O
</s>
<s>
The	O
mapping	O
of	O
chares	O
to	O
processors	O
is	O
transparent	O
to	O
the	O
programmer	O
,	O
and	O
this	O
transparency	O
permits	O
the	O
runtime	O
system	O
to	O
dynamically	O
change	O
the	O
assignment	O
of	O
chares	O
to	O
processors	O
during	O
program	O
execution	O
to	O
support	O
capabilities	O
such	O
as	O
measurement-based	O
load	O
balancing	O
,	O
fault	O
tolerance	O
,	O
automatic	O
checkpointing	O
,	O
and	O
the	O
ability	O
to	O
shrink	O
and	O
expand	O
the	O
set	O
of	O
processors	O
used	O
by	O
a	O
parallel	B-Operating_System
program	I-Operating_System
.	O
</s>
<s>
Applications	O
implemented	O
using	O
Charm++	B-Language
include	O
NAMD	B-Application
(	O
molecular	O
dynamics	O
)	O
and	O
OpenAtom	B-Application
(	O
quantum	O
chemistry	O
)	O
,	O
ChaNGa	O
and	O
SpECTRE	O
(	O
astronomy	O
)	O
,	O
EpiSimdemics	O
(	O
epidemiology	O
)	O
,	O
Cello/Enzo	O
-P	O
(	O
adaptive	O
mesh	O
refinement	O
)	O
,	O
and	O
ROSS	O
(	O
parallel	O
discrete	O
event	O
simulation	O
)	O
.	O
</s>
<s>
Adaptive	O
MPI	B-Application
(	O
AMPI	O
)	O
is	O
an	O
implementation	O
of	O
the	O
Message	B-Application
Passing	I-Application
Interface	I-Application
standard	O
on	O
top	O
of	O
the	O
Charm++	B-Language
runtime	O
system	O
and	O
provides	O
the	O
capabilities	O
of	O
Charm++	B-Language
in	O
a	O
more	O
traditional	O
MPI	B-Application
programming	O
model	O
.	O
</s>
<s>
AMPI	O
encapsulates	O
each	O
MPI	B-Application
process	O
within	O
a	O
user-level	O
migratable	O
thread	O
that	O
is	O
bound	O
within	O
a	O
Charm++	B-Language
object	O
.	O
</s>
<s>
By	O
embedding	O
each	O
thread	O
in	O
a	O
chare	O
,	O
AMPI	O
programs	O
can	O
automatically	O
take	O
advantage	O
of	O
the	O
features	O
of	O
the	O
Charm++	B-Language
runtime	O
system	O
with	O
little	O
or	O
no	O
changes	O
to	O
the	O
MPI	B-Application
program	O
.	O
</s>
<s>
Charm4py	O
allows	O
writing	O
Charm++	B-Language
applications	O
in	O
Python	B-Language
,	O
supporting	O
migratable	O
Python	B-Language
objects	O
and	O
asynchronous	O
remote	O
method	O
invocation	O
.	O
</s>
<s>
Here	O
is	O
some	O
Charm++	B-Language
code	O
for	O
demonstration	O
purposes	O
:	O
</s>
<s>
Adaptive	O
MPI	B-Application
is	O
an	O
implementation	O
of	O
MPI	B-Application
(	O
like	O
MPICH	O
,	O
OpenMPI	O
,	O
MVAPICH	O
,	O
etc	O
.	O
)	O
</s>
<s>
on	O
top	O
of	O
Charm++'s	O
runtime	O
system	O
.	O
</s>
<s>
Users	O
can	O
take	O
pre-existing	O
MPI	B-Application
applications	O
,	O
recompile	O
them	O
using	O
AMPI	O
's	O
compiler	O
wrappers	O
,	O
and	O
begin	O
experimenting	O
with	O
process	O
virtualization	O
,	O
dynamic	O
load	O
balancing	O
,	O
and	O
fault	O
tolerance	O
.	O
</s>
<s>
AMPI	O
implements	O
MPI	B-Application
"	O
ranks	O
"	O
as	O
user-level	O
threads	O
(	O
rather	O
than	O
operating	O
system	O
processes	O
)	O
.	O
</s>
<s>
is	O
a	O
Python	B-Language
parallel	B-Operating_System
computing	I-Operating_System
framework	O
built	O
on	O
top	O
of	O
the	O
Charm++	B-Language
C++	B-Language
runtime	O
,	O
which	O
it	O
uses	O
as	O
a	O
shared	O
library	O
.	O
</s>
<s>
Charm4py	O
simplifies	O
the	O
development	O
of	O
Charm++	B-Language
applications	O
and	O
streamlines	O
parts	O
of	O
the	O
programming	O
model	O
.	O
</s>
<s>
Users	O
are	O
still	O
free	O
to	O
accelerate	O
their	O
application-level	O
code	O
with	O
technologies	O
like	O
Numba	B-Language
.	O
</s>
<s>
Standard	O
ready-to-use	O
binary	O
versions	O
can	O
be	O
installed	O
on	O
Linux	B-Application
,	O
macOS	B-Application
and	O
Windows	O
with	O
pip	B-Application
.	O
</s>
<s>
It	O
is	O
also	O
possible	O
to	O
write	O
hybrid	O
Charm4py	O
and	O
MPI	B-Application
programs	O
.	O
</s>
