Remote Procedure Call
Andy Wang
Operating Systems
COP 4610 / CGS 5765
Primitives to Build Distributed
Applications
 send and receive
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Used to synchronize cooperating processes
running on different machines
Communicate through mailboxes (ports)
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Temporary holding areas for messages
Atomic operations

send/receive the entire message or nothing
More on send and receive
 To put a message to the network
 send(message, destination_mbox)
 receive(buffer, mbox)
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Waits until a message arrives
Copies the message into a given buffer
Remote Procedure Call (RPC)
 Allows you to invoke a procedure on either a
local or remote machine

Client
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RemoteMachineSay(“Meow”);
Server
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MachineSay(“Meow”);
 Implemented on top of two-way messaging
RPC Illustrated
Client (caller)
call
Server (callee)
reply
reply
Client stub
call
Server stub
OS or Network
Procedure Stubs
 Provide the invocation interface programmers
 e.g. foo(int a)
 Client stub

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Build messages (a.k.a. marshalling)
Send messages
Wait for response
Unpack reply
Return result
Server Stub
 Create N threads to wait for requests
 Loop
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Wait for command
Decode and unpack request parameters
(unmarshalling)
Call procedure
Build replay message with results
Send reply
RPC vs. Procedure Call
 From the programmer’s viewpoint

Similar semantics
 Pointers are instantiated before transmission

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Data structures pointed by the pointer are
copied
Processes running on the remote machine is
in a different address space
Implementation Issues
 Stubs are automatically generated
 Need to have a well-known port to talk to
servers
 Server can upgrade the implementation
without recompiling client applications
Interprocess Communication
 RPC is just another way to communicate
between processes
 Example uses

Microkernel operating systems

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Portions of an OS are implemented at the user
level to minimize the kernel-level code
Object linking and embedding (OLE)

Mix-and-match applications
Using RPC for IPC
+ Fault isolation: bugs are unlikely to propagate
across different address spaces
+ Modularity: independent component
upgrades
+ Location transparency: a service can be
provided from local or remote machines
Using RPC for IPC
- Poor performance
- A wide range of failure modes
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A user-level bug can cause a process failure
A kernel-level bug can cause multiple
processes to fail
A network failure, server failure, or an
earthquake can cause multiple machines to
fail