Remote procedure call

Remote procedure call (RPC) is an Inter-process communication technology that allows a computer program to cause a subroutine or procedure to execute in another address space (commonly on another computer on a shared network) without the programmer explicitly coding the details for this remote interaction. That is, the programmer would write essentially the same code whether the subroutine is local to the executing program, or remote. When the software in question is written using object-oriented principles, RPC may be referred to as remote invocation or remote method invocation.

Note that there are many different technologies commonly used to accomplish this which are often incompatible, such as ONC RPC and DCE/RPC.

History and origins

The idea of RPC goes back at least as far as 1976, when it was described in RFC 707. One of the first business uses of RPC was by Xerox under the name "Courier" in 1981. The first popular implementation of RPC on Unix was Sun's RPC (now called ONC RPC), used as the basis for Sun's NFS. ONC RPC is still widely used today on several platforms.

Another early Unix implementation was Apollo Computer's Network Computing System (NCS). NCS later was used as the foundation of DCE/RPC in the OSF's Distributed Computing Environment (DCE). A decade later Microsoft adopted DCE/RPC as the basis of their Microsoft RPC (MSRPC) mechanism, and implemented DCOM atop it. Around the same time (mid-90's), Xerox PARC's ILU, and the Object Management Group's CORBA, offered another RPC paradigm based on distributed objects with an inheritance mechanism.

Message passing

RPC is an obvious and popular paradigm for implementing the client-server model of distributed computing. An RPC is initiated by the "client" sending a request message to a known remote "server" in order to execute a specified procedure using supplied parameters. A response is returned to the client where the application continues along with its process. There are many variations and subtleties in various implementation, resulting in a variety of different (incompatible) RPC protocols. While the server is processing the call, the client is blocked (it waits until the server has finished processing until resuming execution).

An important difference between remote procedure calls and local calls is that remote calls can fail because of unpredictable network problems. Also, callers generally must deal with such failures without knowing whether the remote procedure was actually invoked. Idempotent procedures (those which have no additional effects if called more than once) are easily handled, but enough difficulties remain that code which calls remote procedures is often confined to carefully written low-level subsystems.

Standard contact mechanisms

In order to allow servers to be accessed by differing clients, a number of standardized RPC systems have been created. Most of these use an interface description language (IDL) to allow various platforms to call the RPC.

The IDL files can then be used to generate code to interface between the client and server. The most common tool used for this is RPCGEN.

Other RPC analogues

RPC analogues found elsewhere:
* Java's Java Remote Method Invocation (Java RMI) API provides similar functionality to standard UNIX RPC methods.
* XML-RPC is an RPC protocol which uses XML to encode its calls and HTTP as a transport mechanism.
* Microsoft .NET Remoting offers RPC facilities for distributed systems implemented on the Windows platform.
* RPyC implements RPC mechanisms in Python, with support for asynchronous calls.
* Facebook's Thrift protocol and framework.
* CORBA provides remote procedure invocation through an intermediate layer called the "Object Request Broker"

Web services RPC

See also

* Local Procedure Call
* SOAP
* HTTP
* ODBC
* Remote function call

External links

*RFC 1057 - Specifies version 1 of ONC RPC
*RFC 1831 - Specifies version 2 of ONC RPC
* [http://www.cs.cf.ac.uk/Dave/C/node33.html Remote Procedure Calls (RPC)] — A tutorial on ONC RPC by Dr Dave Marshall of Cardiff University