<s>
In	O
distributed	B-Architecture
computing	I-Architecture
,	O
a	O
remote	B-Operating_System
procedure	I-Operating_System
call	I-Operating_System
(	O
RPC	O
)	O
is	O
when	O
a	O
computer	O
program	O
causes	O
a	O
procedure	O
(	O
subroutine	O
)	O
to	O
execute	O
in	O
a	O
different	O
address	B-General_Concept
space	I-General_Concept
(	O
commonly	O
on	O
another	O
computer	O
on	O
a	O
shared	O
network	O
)	O
,	O
which	O
is	O
written	O
as	O
if	O
it	O
were	O
a	O
normal	O
(	O
local	O
)	O
procedure	O
call	O
,	O
without	O
the	O
programmer	O
explicitly	O
writing	O
the	O
details	O
for	O
the	O
remote	O
interaction	O
.	O
</s>
<s>
This	O
is	O
a	O
form	O
of	O
client	O
–	O
server	O
interaction	O
(	O
caller	O
is	O
client	O
,	O
executor	O
is	O
server	O
)	O
,	O
typically	O
implemented	O
via	O
a	O
request	B-Protocol
–	I-Protocol
response	I-Protocol
message-passing	O
system	O
.	O
</s>
<s>
In	O
the	O
object-oriented	B-Language
programming	I-Language
paradigm	O
,	O
RPCs	O
are	O
represented	O
by	O
remote	O
method	O
invocation	O
(	O
RMI	O
)	O
.	O
</s>
<s>
RPCs	O
are	O
a	O
form	O
of	O
inter-process	B-Operating_System
communication	I-Operating_System
(	O
IPC	B-Operating_System
)	O
,	O
in	O
that	O
different	O
processes	O
have	O
different	O
address	B-General_Concept
spaces	I-General_Concept
:	O
if	O
on	O
the	O
same	O
host	O
machine	O
,	O
they	O
have	O
distinct	O
virtual	O
address	B-General_Concept
spaces	I-General_Concept
,	O
even	O
though	O
the	O
physical	O
address	B-General_Concept
space	I-General_Concept
is	O
the	O
same	O
;	O
while	O
if	O
they	O
are	O
on	O
different	O
hosts	O
,	O
the	O
physical	O
address	B-General_Concept
space	I-General_Concept
is	O
different	O
.	O
</s>
<s>
Request	B-Protocol
–	I-Protocol
response	I-Protocol
protocols	O
date	O
to	O
early	O
distributed	B-Architecture
computing	I-Architecture
in	O
the	O
late	O
1960s	O
,	O
theoretical	O
proposals	O
of	O
remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
as	O
the	O
model	O
of	O
network	O
operations	O
date	O
to	O
the	O
1970s	O
,	O
and	O
practical	O
implementations	O
date	O
to	O
the	O
early	O
1980s	O
.	O
</s>
<s>
Bruce	O
Jay	O
Nelson	O
is	O
generally	O
credited	O
with	O
coining	O
the	O
term	O
"	O
remote	B-Operating_System
procedure	I-Operating_System
call	I-Operating_System
"	O
in	O
1981	O
.	O
</s>
<s>
Remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
used	O
in	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
trace	O
their	O
roots	O
back	O
to	O
the	O
RC	O
4000	O
multiprogramming	O
system	O
,	O
which	O
used	O
a	O
request-response	B-Protocol
communication	O
protocol	O
for	O
process	O
synchronization	O
.	O
</s>
<s>
The	O
idea	O
of	O
treating	O
network	O
operations	O
as	O
remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
goes	O
back	O
at	O
least	O
to	O
the	O
1970s	O
in	O
early	O
ARPANET	O
documents	O
.	O
</s>
<s>
In	O
1978	O
,	O
Per	O
Brinch	O
Hansen	O
proposed	O
Distributed	O
Processes	O
,	O
a	O
language	O
for	O
distributed	B-Architecture
computing	I-Architecture
based	O
on	O
"	O
external	O
requests	O
"	O
consisting	O
of	O
procedure	O
calls	O
between	O
processes	O
.	O
</s>
<s>
One	O
of	O
the	O
earliest	O
practical	O
implementations	O
was	O
in	O
1982	O
by	O
Brian	O
Randell	O
and	O
colleagues	O
for	O
their	O
Newcastle	B-Protocol
Connection	I-Protocol
between	O
UNIX	B-Application
machines	O
.	O
</s>
<s>
Lupine	O
automatically	O
generated	O
stubs	B-Operating_System
,	O
providing	O
type-safe	O
bindings	O
,	O
and	O
used	O
an	O
efficient	O
protocol	O
for	O
communication	O
.	O
</s>
<s>
The	O
first	O
popular	O
implementation	O
of	O
RPC	O
on	O
Unix	B-Application
was	O
Sun	B-Protocol
's	I-Protocol
RPC	I-Protocol
(	O
now	O
called	O
ONC	B-Protocol
RPC	I-Protocol
)	O
,	O
used	O
as	O
the	O
basis	O
for	O
Network	B-Protocol
File	I-Protocol
System	I-Protocol
(	O
NFS	O
)	O
.	O
</s>
<s>
In	O
the	O
1990s	O
,	O
with	O
the	O
popularity	O
of	O
object-oriented	B-Language
programming	I-Language
,	O
an	O
alternative	O
model	O
of	O
remote	O
method	O
invocation	O
(	O
RMI	O
)	O
was	O
widely	O
implemented	O
,	O
such	O
as	O
in	O
Common	B-Architecture
Object	I-Architecture
Request	I-Architecture
Broker	I-Architecture
Architecture	I-Architecture
(	O
CORBA	B-Architecture
,	O
1991	O
)	O
and	O
Java	B-Language
remote	I-Language
method	I-Language
invocation	I-Language
.	O
</s>
<s>
RPC	O
is	O
a	O
request	B-Protocol
–	I-Protocol
response	I-Protocol
protocol	O
.	O
</s>
<s>
While	O
the	O
server	O
is	O
processing	O
the	O
call	O
,	O
the	O
client	O
is	O
blocked	O
(	O
it	O
waits	O
until	O
the	O
server	O
has	O
finished	O
processing	O
before	O
resuming	O
execution	O
)	O
,	O
unless	O
the	O
client	O
sends	O
an	O
asynchronous	O
request	O
to	O
the	O
server	O
,	O
such	O
as	O
an	O
XMLHttpRequest	B-Protocol
.	O
</s>
<s>
An	O
important	O
difference	O
between	O
remote	B-Operating_System
procedure	I-Operating_System
calls	I-Operating_System
and	O
local	O
calls	O
is	O
that	O
remote	O
calls	O
can	O
fail	O
because	O
of	O
unpredictable	O
network	O
problems	O
.	O
</s>
<s>
The	O
client	O
calls	O
the	O
client	O
stub	B-Operating_System
.	O
</s>
<s>
The	O
call	O
is	O
a	O
local	B-Operating_System
procedure	I-Operating_System
call	I-Operating_System
,	O
with	O
parameters	O
pushed	O
on	O
to	O
the	O
stack	O
in	O
the	O
normal	O
way	O
.	O
</s>
<s>
The	O
client	O
stub	B-Operating_System
packs	O
the	O
parameters	O
into	O
a	O
message	O
and	O
makes	O
a	O
system	O
call	O
to	O
send	O
the	O
message	O
.	O
</s>
<s>
Packing	O
the	O
parameters	O
is	O
called	O
marshalling	B-Application
.	O
</s>
<s>
The	O
client	O
's	O
local	O
operating	B-General_Concept
system	I-General_Concept
sends	O
the	O
message	O
from	O
the	O
client	O
machine	O
to	O
the	O
server	O
machine	O
.	O
</s>
<s>
The	O
local	O
operating	B-General_Concept
system	I-General_Concept
on	O
the	O
server	O
machine	O
passes	O
the	O
incoming	O
packets	O
to	O
the	O
server	O
stub	B-Operating_System
.	O
</s>
<s>
The	O
server	O
stub	B-Operating_System
unpacks	O
the	O
parameters	O
from	O
the	O
message	O
.	O
</s>
<s>
Unpacking	O
the	O
parameters	O
is	O
called	O
unmarshalling	B-Application
.	O
</s>
<s>
Finally	O
,	O
the	O
server	O
stub	B-Operating_System
calls	O
the	O
server	O
procedure	O
.	O
</s>
<s>
Most	O
of	O
these	O
use	O
an	O
interface	B-General_Concept
description	I-General_Concept
language	I-General_Concept
(	O
IDL	O
)	O
to	O
let	O
various	O
platforms	O
call	O
the	O
RPC	O
.	O
</s>
<s>
Java	B-Language
's	O
Java	B-Language
Remote	I-Language
Method	I-Language
Invocation	I-Language
(	O
Java	B-Language
RMI	I-Language
)	O
API	O
provides	O
similar	O
functionality	O
to	O
standard	O
Unix	B-Application
RPC	O
methods	O
.	O
</s>
<s>
RPyC	B-Library
implements	O
RPC	O
mechanisms	O
in	O
Python	O
,	O
with	O
support	O
for	O
asynchronous	O
calls	O
.	O
</s>
<s>
Distributed	B-Operating_System
Ruby	I-Operating_System
(	O
DRb	O
)	O
allows	O
Ruby	O
programs	O
to	O
communicate	O
with	O
each	O
other	O
on	O
the	O
same	O
machine	O
or	O
over	O
a	O
network	O
.	O
</s>
<s>
Erlang	B-Operating_System
is	O
process	O
oriented	O
and	O
natively	O
supports	O
distribution	O
and	O
RPCs	O
via	O
message	O
passing	O
between	O
nodes	O
and	O
local	O
processes	O
alike	O
.	O
</s>
<s>
Elixir	B-Language
builds	O
on	O
top	O
of	O
the	O
Erlang	B-Operating_System
VM	O
and	O
allows	O
process	O
communication	O
(	O
Elixir/Erlang	O
processes	O
,	O
not	O
OS	O
processes	O
)	O
of	O
the	O
same	O
network	O
out-of-the-box	O
via	O
Agents	O
and	O
message	O
passing	O
.	O
</s>
<s>
Action	B-Protocol
Message	I-Protocol
Format	I-Protocol
(	O
AMF	O
)	O
allows	O
Adobe	B-Operating_System
Flex	I-Operating_System
applications	O
to	O
communicate	O
with	O
back-ends	B-Architecture
or	O
other	O
applications	O
that	O
support	O
AMF	O
.	O
</s>
<s>
Remote	B-General_Concept
Function	I-General_Concept
Call	I-General_Concept
is	O
the	O
standard	O
SAP	O
interface	O
for	O
communication	O
between	O
SAP	O
systems	O
.	O
</s>
<s>
D-Bus	B-Language
open	O
source	O
IPC	B-Operating_System
program	O
provides	O
similar	O
function	O
to	O
CORBA	B-Architecture
.	O
</s>
<s>
XML-RPC	B-Protocol
is	O
an	O
RPC	O
protocol	O
that	O
uses	O
XML	B-Protocol
to	O
encode	O
its	O
calls	O
and	O
HTTP	B-Protocol
as	O
a	O
transport	O
mechanism	O
.	O
</s>
<s>
SOAP	B-Application
is	O
a	O
successor	O
of	O
XML-RPC	B-Protocol
and	O
also	O
uses	O
XML	B-Protocol
to	O
encode	O
its	O
HTTP-based	O
calls	O
.	O
</s>
<s>
ZeroC	O
's	O
Internet	B-Operating_System
Communications	I-Operating_System
Engine	I-Operating_System
(	O
Ice	O
)	O
distributed	B-Architecture
computing	I-Architecture
platform	O
.	O
</s>
<s>
Etch	B-Protocol
framework	O
for	O
building	O
network	O
services	O
.	O
</s>
<s>
Apache	B-Protocol
Thrift	I-Protocol
protocol	O
and	O
framework	O
.	O
</s>
<s>
CORBA	B-Architecture
provides	O
remote	O
procedure	O
invocation	O
through	O
an	O
intermediate	O
layer	O
called	O
the	O
object	O
request	O
broker	O
.	O
</s>
<s>
Libevent	B-Language
provides	O
a	O
framework	O
for	O
creating	O
RPC	O
servers	O
and	O
clients	O
.	O
</s>
<s>
Windows	B-Application
Communication	I-Application
Foundation	I-Application
is	O
an	O
application	O
programming	O
interface	O
in	O
the	O
.NET	B-Application
framework	I-Application
for	O
building	O
connected	O
,	O
service-oriented	O
applications	O
.	O
</s>
<s>
Microsoft	B-Application
.NET	I-Application
Remoting	B-General_Concept
offers	O
RPC	O
facilities	O
for	O
distributed	B-Architecture
systems	I-Architecture
implemented	O
on	O
the	O
Windows	O
platform	O
.	O
</s>
<s>
It	O
has	O
been	O
superseded	O
by	O
WCF	B-Application
.	O
</s>
<s>
The	O
Open	O
Software	O
Foundation	O
DCE/RPC	B-General_Concept
Distributed	B-Architecture
Computing	I-Architecture
Environment	O
(	O
also	O
implemented	O
by	O
Microsoft	O
)	O
.	O
</s>
<s>
Google	B-Protocol
Protocol	I-Protocol
Buffers	I-Protocol
(	O
protobufs	B-Protocol
)	O
package	O
includes	O
an	O
interface	B-General_Concept
definition	I-General_Concept
language	I-General_Concept
used	O
for	O
its	O
RPC	O
protocols	O
open	O
sourced	O
in	O
2015	O
as	O
gRPC	B-Application
.	O
</s>
<s>
WAMP	B-Operating_System
combines	O
RPC	O
and	O
Publish-Subscribe	B-Operating_System
into	O
a	O
single	O
,	O
transport-agnostic	O
protocol	O
.	O
</s>
<s>
Google	B-Language
Web	I-Language
Toolkit	I-Language
uses	O
an	O
asynchronous	O
RPC	O
to	O
communicate	O
to	O
the	O
server	O
service	O
.	O
</s>
<s>
Apache	B-Operating_System
Avro	I-Operating_System
provides	O
RPC	O
where	O
client	O
and	O
server	O
exchange	O
schemas	O
in	O
the	O
connection	O
handshake	O
and	O
code	O
generation	O
is	O
not	O
required	O
.	O
</s>
