1. Operating Systems {week 11a}
Rensselaer Polytechnic Institute
CSCI-4210 – Operating Systems
David Goldschmidt, Ph.D.
Operating Systems {week 11a}

2. Interprocess communication (IPC)
Why is it beneficial for an operating system to enable processes to communicate with one another?
Share information
Cooperation
Computational speed-up via parallel programming
Modularity of program design
Convenience

3. IPC mechanisms Message Passing Shared Memory both IPC mechanisms
require a protocol
and synchronization

4. Client-server communication
Processes may communicate on the same machine or across multiple machines
Use sockets for interprocess client-server communication
Use remote procedure calls (RPCs) to call procedures across a network
In Java, use remote method invocation (RMI) to call a method on an object in a different virtual machine

5. Remote procedure calls (i)

6. Remote procedure calls (ii)
Using RPC, heterogeneous operating systems can interact with one another

7. Marshaling parameters
RPCs can be made across a mix of machines and operating systems
All parameters must be marshaled to ensure proper interpretation
Consider date representations
YYYY-MM-DD or MM-DD-YYYY or DD-MM-YYYY
Also consider big endian versus little endian integer representations
(see

8. Remote method invocation
RMI is a Java mechanism similar to RPCs
RMI enables a running Java program to call a method on a remote object running on a separate Java Virtual Machine
this requires
object serialization

9. <ip-address>:<port>
Sockets (i)
A socket is an endpoint for communication
Communication takes place over a pair of sockets
<ip-address>:<port>
server
:80
listener socket
client
:9500
socket
:8123
socket

10. Sockets (ii)
Pitfalls of socket-based communication between client and server include:
Once a server binds to a port, no other program may listen on that port
If client and server do not obey the rules of the protocol, errors occur

11. Transmitting objects via sockets
In Java, we transmit primitive data types (e.g. int, double) using DataInputStream and DataOutputStream
To transmit objects, use ObjectInputStream and ObjectOutputStream instead
server
client
this requires
object serialization

12. Serializing objects (i)
Objects exist in a JVM’s memory space
To transmit an object over a socket, we must first serialize the object
For an object to be serializable, its class definition must implement the java.io.Serializable interface
Also useful for saving runtime objects to a file

13. Serializing objects (ii)
The Serializable interface has no methods
Simply identifies a class as being serializable
And enables the use of readObject() and writeObject() methods of ObjectInputStream and ObjectOutputStream
Student
object
Student
object
network
serialized object
writeObject()
readObject()

14. Serializing objects (iii)
Classes that are not serializable include:
java.lang.Thread
java.io.OutputStream
java.net.Socket
etc.
Such classes refer to operating system resources, which are not serializable

15. Serializing objects (iv)
Serialized objects are assigned a unique identifier as a means to version control
If you write object X to a socket or file, then modify the source code of class X and recompile the .class file, loading object X results in an InvalidClassException runtime exception
All processes must be using the same version