1. Learning Objectives
Understanding the difference between processes and threads.
Understanding process migration and load distribution.
Understanding Process Inter-process Communication in Distributed Systems
Lecture 2

2. The Kernel
The kernel is a (often memory resident) part of the operating system that has access rights to ALL system resources.
The kernel of a distributed system usually has access only to local resources.
? What o.s. components should be part of the kernel?
Lecture 2

3. Kernel Types Monolithic Kernel Microkernel Unix, VMS.
Chorus (base technology for JavaOS)
Mach
more suitable for distributed computing
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4. Processes
Process is a fundamental concept of computer system operation : it is a program in execution.
? What are properties of a process?
? What constitutes a process?
? What does a process need in order to accomplish its task?
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5. Process Management Process management in distributed systems involves:
process creation
process type identification
process migration
process scheduling
process status control
process termination and clean up
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6. Types of processes in distributed and parallel systems.
Indivisible processes (entire process must be assign to a single processor).
Divisible processes (a process may be subdivided into smaller sub-processes, tasks, or threads.)
TIG (Task Interaction Graph) represents relationships between tasks of a divisible process. (see box 2.4 p.42)
Lecture 2

7. Load Distribution and Process Migration
Process migration involves relocation of a process to remote processor (computer).
Goal of load distribution:
balance the job load among computers in the system
provide better response time of computations
Lecture 2

8. Two Components of Load Balancing Algorithms
Information Gathering
gather info about loads of other processors and select a suitable migration partner
e.g. identifies idle processors, estimate cost of migration to various sites
Process Selection
select a process to migrate
e.g. what is the communication delay for migrating a process, how to accommodate differences in heterogeneous systems
Lecture 2

9. External Data Representation
Heterogeneous systems imply different CPUs, different software configurations and different data representation
External Data Representation is a common representation of data used in heterogeneous systems. External Data Representation greatly reduces the amount of time required to perform cross-platform process migration.
Lecture 2

10. Benefits of External Data Representation
Study figures 2.6 and 2.7 and solve problem 2.9 on page 51.
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11. Load balancing decision examples
Consider the formula for Total_Weight on page 50. Use this formula with Weighting 1 parameters (0.25, 0.25, 0.25, 0.25) in order to determine which is the best location for process migration from exercise 2.6.
Lecture 2

12. Threads Thread is a basic unit of process execution.
“Mini-process” (“lightweight process)
Operating system allowing for multiple threads of execution are referred as multi-threaded (Windows NT, 2000, Unix)
Languages that support multithreading include C, C++, Java.
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13. Thread Properties A process may have multiple threads of control.
Each thread has its own program counter and stack, register set, child threads, and state.
Threads share address space and global variables.
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14. Threads versus Processes
Per Thread Items PC
Stack
Register set
Child threads
State
Per Process Items
Address space
Global variables
Open files
Child processes
Signals/IPC
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15. Multithreaded Support
Posix.1c specifies a standard for threads and their implementation.
Posix Threads
Java support for multithreaded programming
Threads are treated like other objects.
Must be instantiated with a parameter that is a runable object (runable objects define a run() method)
See box 2.2 p. 37 for Thread constructor prototypes and sample methods
Lecture 2

16. Multithreaded Code Process versus threads example
Posix Threads Example
Multithreaded programming paradigms
specialist paradigm
client/server paradigm
assembly line paradigm
? Read paragraph p.34 and answer question 2.2. on page 49.
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17. Processes and Threads in Windows’98
Windows 95/98 NT and 2000 utilize multithreading.
Check the following file to processes and threads in Windows
C:\Program Files\DevStudio\Vc\bin\Win95\Pview95
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18. Inter-process Communication
Inter-process Communication is an essential component of distributed computing.
WHY?
Lecture 2

19. Common IPC Primitives Messages Pipes Sockets
RPCs (Remote Procedure Calls)
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20. Message Passing
Message passing involves copying of data from one process address space to another process address space.
Primitives used:
msgSent (dest, text)
msgReceive (source, text)
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21. Blocking and Non-blocking Primitives
Blocking msgSend waits (blocks awaiting) for acknowledgment
Blocking msgReceive waits (block awaiting) for the messages
Sometimes called synchronous
Non-blocking msgSend sends the message and does not wait for ack.
Non-blocking msgReceive does not wait for a messages.
Sometimes called asynchronous
Lecture 2

22. Message Addressing One-to-many (multiple receivers, single sender)
Many-to-one (multiple senders, one receiver)
Many-to-many (multiple receivers, multiple senders)
Lecture 2

23. Pipes Communication takes via a memory buffer. One-to-one type
Unnamed pipes
allow for communication between related processes (e.g. parent and child)
Named pipes
allow for communication between unrelated processes (see Box 3.3 p.64 for details)
Lecture 2

24. Sockets Used for communication across the network.
Low level primitives.
Requires 6-8 steps (create socket, bind, connect, listen, send receive, shutdown.)
Supported by Unix and Java (see box and 3.5 pp. 70 and 71)
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25. Remote Procedure Calls
RPC is a high level, blocking primitive.
Allows communication between remote computers using techniques similar to traditional procedure calls.
Allows for complex data structures to be passed as parameters.
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26. RPC features Parameter Type Data Type Support Parameter Marshalling
RPC Binding
RPC Authentication
RPC Semantics
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27. RPC Semantics At-Most-Once At-Least-Once Last-of-Many-Call Idempotent
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28. Parameter Type Input only Output only Input/output per value
receive from the server
Input/output
call by value/results
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29. Data Type Support
Allow/disallow some data types (e.g. pointers or complex structures.)
Limit the number of parameters passed
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30. Parameter Marshalling
Packing of parameters to minimize the amount of information sent across the network.
Use of stubs on client and server sites.
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31. RPC Binding Binding involves Binding can be accomplished at
port mapping for the server
assigning a port handler for the client
see fig p.74
Binding can be accomplished at
compile time
link time
run time
Lecture 2

32. RPC Authentication
Client/server authentication might be needed to assure security of data transmisison.
Lecture 2