Remote Procedure Call
What is RPC
Remote Procedure Calls, or RPC's for short, are a means to have certain services executed by some code that lies in an different process (maybe even on a machine located somewhere in the network), instead of being available locally. This is a common practice, employed e.g. by application servers or web applications.
Popular protocols for RPC's are COM+, Corba, or SOAP.
Remote Procedure Calls in a nutshell
A RPC system relies on a compiler that will generate helper code from a high-level interface description (usually IDL, "Interface Description Language"). The 'client' code that wish to call a service will actually call a proxy function locally, passing it the arguments for the remote code. The proxy then marshalls (or serializes) the arguments according so that they fit in a flat buffer and send that buffer to the server code (for instance involving a UDP packet or some local message queue) and waits for response.
On its side, the server suddenly receive the marshalled packet and will pass it to a stub that will re-create the data (unmarshall) and call the real service procedure, getting back the results and marshall them back in a message to the client.
( client ) ( server )
| ^
| sayHello("World") | serverSayHello("World")
V |
+------\ - - - <channel>- - - - \-------+
| PROXY > -> iXX mYY Str'W o r l d \0' -> > STUB |
+------/ - - - - - |- - - - /-------+
|
marshalled message
^ ^
/_\ /_\
: :
: :
: |------------|\ :
: | .idl file L_\ :
+ - compiler - | (describing | - compiler +
| interface) |
+--------------+