Remote Procedure Call (RPC) is a protocol that one program can use to request a service from a program located in another computer on a network without having to understand the network's details. RPC is used to call other processes on the remote systems like a local system. A procedure call is also sometimes known as a function call or a subroutine call.
RPC uses the client-server model. The requesting program is a client, and the service providing program is the server. Like a regular or local procedure call, an RPC is a synchronous operation requiring the requesting program to be suspended until the results of the remote procedure are returned. However, the use of lightweight processes or threads that share the same address space enables multiple RPCs to be performed concurrently.
The interface definition language (IDL)—the specification language used to describe a software component's application programming interface (API)—is commonly used in RPC software. In this case, IDL provides a bridge between the machines at either end of the link that may be using different operating systems and computer languages.
When program statements that use the RPC framework are compiled into an executable program, a stub is included in the compiled code that acts as the representative of the remote procedure code. When the program is run and the procedure call is issued, the stub receives the request and forwards it to a client runtime program in the local computer. The first time the client stub is invoked, it contacts a name server to determine the transport address where the server resides.
The client runtime program has the knowledge of how to address the remote computer and server application and sends the message across the network that requests the remote procedure. Similarly, the server includes a runtime program and stub that interface with the remote procedure itself. Response-request protocols are returned the same way.
When a remote procedure call is invoked, the calling environment is suspended, the procedure parameters are transferred across the network to the environment where the procedure is to execute, and the procedure is then executed in that environment.
When the procedure finishes, the results are transferred back to the calling environment, where execution resumes as if returning from a regular procedure call.
During an RPC, the following steps take place: