Message Passing Systems (Part 1)

Summary

This lecture delves into message passing systems, a type of inter-process communication that enables processes to exchange messages without sharing memory. It's particularly beneficial for distributed environments, such as internet chat, where processes on different systems communicate via networks. The lecture explains the basic operations of sending and receiving messages, discusses fixed and variable message sizes, and touches on the complexities of system implementation. It also introduces various methods for logically implementing communication links and the associated challenges.

Takeaways

• 📚 The lecture focuses on message passing systems as a form of inter-process communication (IPC), contrasting with shared memory systems.
• 🌐 Message passing is particularly useful in distributed environments where processes may reside on different computers connected by a network.
• 💬 In message passing systems, processes communicate and synchronize without sharing the same address space, unlike shared memory systems.
• 🔗 The system provides two fundamental operations: 'send message' and 'receive message' for processes to communicate with each other.
• 📦 Messages can be of fixed or variable length, with fixed size making system implementation easier but programming more challenging, and vice versa for variable size.
• 🛠️ Fixed size messages simplify system-level implementation but complicate programming due to the restriction on message size.
• 🔄 Variable size messages require a more complex system implementation but simplify programming by allowing flexibility in message size.
• 🔗 For processes to communicate, a communication link must exist between them, which can be implemented in various logical ways.
• 🔍 The lecture will cover methods for logically implementing communication links and the associated issues like naming, synchronization, and buffering in the second part.
• 🤖 The script introduces the concept of message passing systems and sets the stage for a deeper dive into its features and operation mechanisms.
• 🎓 The lecture aims to clarify the workings of message passing systems for students, providing foundational knowledge for further study.

Q & A

What is the main difference between shared memory systems and message passing systems in inter-process communication?

Shared memory systems allow processes to communicate by sharing a portion of memory within the address space of one process, whereas message passing systems enable communication between processes without sharing the same address space, which is especially useful in distributed environments.

Why are message passing systems particularly useful in a distributed environment?

Message passing systems are useful in distributed environments because they allow processes on different computers, connected by a network, to communicate by sending and receiving messages without the need for a shared memory region that can be accessed by both processes.

What are the two basic operations provided by a message passing facility?

The two basic operations provided by a message passing facility are 'send message', which allows a process to send a message to another process, and 'receive message', which allows the recipient process to receive the message from the sender.

What are the two types of message sizes that can be sent in a message passing system?

The two types of message sizes are fixed size and variable size. Fixed size messages have a predetermined size that cannot be exceeded, while variable size messages can vary in size, being either large or small.

How does the implementation of fixed size messages affect the system level and the task of programming?

Fixed size message implementation is straightforward at the system level because the system is designed to handle messages of a fixed size. However, it makes programming more difficult because programmers must ensure that the messages do not exceed the fixed size, which can be restrictive.

What is the advantage of variable size messages in terms of programming ease?

Variable size messages require a more complex system level implementation but offer the advantage of simplifying the programming task. Programmers do not have restrictions on the size of the messages, making it easier to handle communication between processes with messages of varying sizes.

What is a communication link in the context of message passing systems?

A communication link in message passing systems is a logical connection between two processes that allows them to send and receive messages. It is necessary for processes to communicate with each other in the absence of shared memory.

What are some of the methods for logically implementing a communication link between processes in a message passing system?

Some methods for logically implementing a communication link include direct or indirect communication, synchronous or asynchronous communication, and automatic or explicit buffering.

What are some of the issues associated with features like naming, synchronization, and buffering in message passing systems?

Issues associated with features like naming, synchronization, and buffering involve how processes identify each other (naming), how they coordinate message sending and receiving (synchronization), and how messages are stored temporarily before being sent or after being received (buffering).

How does the message passing system facilitate communication between two processes, P and Q?

For processes P and Q to communicate using a message passing system, they must be able to send and receive messages from each other. This requires a communication link between them, which can be implemented in various ways as discussed in the lecture.

What will be discussed in the second part of the lecture on message passing systems?

The second part of the lecture will delve into the methods for logically implementing a communication link and the issues associated with features such as naming, synchronization, and buffering in message passing systems.

Outlines

00:00

📚 Introduction to Message Passing Systems

This paragraph introduces the concept of message passing systems as a method of inter-process communication, contrasting it with shared memory systems. It explains that message passing allows processes to communicate and synchronize without sharing the same address space, which is particularly beneficial in distributed environments like internet chat. The paragraph also outlines the basic operations of send and receive messages, which are fundamental to message passing facilities, and touches on the differences between fixed and variable length messages in terms of system implementation and programming complexity.

05:01

🔌 Fixed vs. Variable Message Sizes in Message Passing

The second paragraph delves into the specifics of fixed and variable size messages within message passing systems. It discusses how fixed size messages simplify system-level implementation but complicate programming due to the inflexibility in message size. Conversely, variable size messages demand a more complex system implementation but ease the programming process by removing size restrictions. The paragraph also emphasizes the importance of a communication link between processes for message passing and hints at various methods for logically implementing such links, which will be detailed in a subsequent lecture.

10:04

🔄 Upcoming Discussion on Link Implementation and Communication Features

The final paragraph sets the stage for the second part of the lecture, where the focus will be on the methods for logically implementing communication links and addressing associated issues such as naming, synchronization, and buffering. It provides a brief overview of the topics to be covered and assures the audience that these aspects of message passing systems will be thoroughly explained in the continuation of the lecture series.

Keywords

💡Message Passing Systems

Message Passing Systems are a type of inter-process communication mechanism that allows processes to communicate and synchronize their actions without sharing the same address space. This is particularly useful in distributed environments where processes may reside on different computers connected by a network. In the video, this concept is the central theme, as it is contrasted with shared memory systems and explained as a way for processes to exchange information through messages rather than shared memory regions.

💡Inter-Process Communication (IPC)

Inter-Process Communication refers to the mechanisms that allow different processes to exchange information. In the context of the video, IPC is discussed in relation to both shared memory systems and message passing systems. The script explains how shared memory and message passing are two distinct methods for processes to communicate, with message passing being the focus of the lecture.

💡Shared Memory Systems

Shared Memory Systems are a method of IPC where two or more processes communicate by sharing a portion of memory that resides in the address space of one of the processes. The script contrasts this with message passing systems, highlighting that in shared memory systems, processes write to or read from a shared memory region to communicate, whereas in message passing, communication is done through the exchange of messages.

💡Distributed Environment

A Distributed Environment is a network of computers that work together and communicate with each other. In the video, the distributed environment is used as an example to illustrate the utility of message passing systems. It is mentioned in the context of internet chat, where processes on different systems communicate by sending and receiving messages over a network.

💡Send Message Operation

The 'Send Message' operation is a fundamental part of message passing systems. It allows a process to transmit a message to another process with which it wishes to communicate. The script explains this operation as one of the two basic operations provided by a message passing facility, essential for processes to initiate communication.

💡Receive Message Operation

The 'Receive Message' operation complements the 'Send Message' operation in message passing systems. It enables the recipient process to get the message sent by another process. The video script describes this as the operation that allows processes to receive communication from their counterparts.

💡Fixed Size Messages

Fixed Size Messages are a type of message in message passing systems where the size or length of the message is predetermined and cannot be exceeded. The script discusses the implementation of fixed size messages as being straightforward at the system level but more challenging for programmers who must ensure that their messages adhere to the fixed size constraint.

💡Variable Size Messages

Variable Size Messages, in contrast to fixed size messages, allow for the message size to vary. The script explains that while implementing variable size messages requires a more complex system level design, it simplifies the programming task as there are no restrictions on the size of the messages being sent.

💡Communication Link

A Communication Link is a logical connection established between two processes that need to communicate with each other in a message passing system. The script emphasizes the necessity of such a link for processes to send and receive messages, unlike in shared memory systems where communication occurs through a shared memory region.

💡Direct Communication

Direct Communication is one of the methods for logically implementing a link in message passing systems. The script mentions this as a method without going into detail, but it implies that in direct communication, a process sends a message directly to another specific process, which is an essential aspect of how message passing systems facilitate communication.

💡Synchronous Communication

Synchronous Communication is a concept related to message passing where the sender process waits for the receiver process to acknowledge the receipt of the message before proceeding. The script does not delve into this concept deeply, but it is listed as one of the methods for implementing communication in message passing systems, indicating its importance in the synchronization of processes.

Highlights

Introduction to message passing systems as a type of inter-process communication.

Comparison with shared memory systems where communication occurs through shared regions of memory.

Message passing systems work without sharing the same address space, beneficial in distributed environments.

Usefulness of message passing in scenarios like internet chat where processes are on different systems.

Basic operations of message passing systems: send message and receive message.

Message sizes can be fixed or variable, impacting system implementation and programming complexity.

Fixed size messages simplify system implementation but complicate programming due to size restrictions.

Variable size messages require complex system implementation but ease programming tasks.

The necessity of a communication link between processes for message passing.

Several methods for logically implementing a communication link for message passing.

Different methods include direct or indirect communication, synchronous or asynchronous messaging.

Automatic or explicit buffering as a method for message passing system implementation.

Issues related to naming, synchronization, and buffering in message passing systems.

The importance of addressing these issues for effective communication between processes.

The lecture will continue to explore methods and issues in the second part, indicating a comprehensive coverage.

Practical applications of message passing systems in modern distributed computing environments.

The theoretical underpinnings of message passing systems and their significance in computer science.

Transcripts

in this lecture we'll be studying about

message passing systems in the previous

lecture we have studied about another

kind of inter-process communication

which was a shared memory systems in

which if two process wants to

communicate they do so by sharing a

portion of memory which resides in the

address space of one of the processes

and when they want to communicate they

write to that shared memory or they read

from that shared memory now we'll be

discussing the next kind of

inter-process communication which is the

message passing systems so we have seen

a brief introduction about this message

passing systems when we discussed the

lecture of inter-process communication

but in this lecture we'll be studying in

more detail about this message passing

system and how this message passing

systems actually work

so message passing provides a mechanism

to allow processes to communicate and to

synchronize their actions without

sharing the same address space

and is particularly useful in a

distributed environment

where the communicating processes may

reside on different computers connected

by a network so as i already told you

when we discuss about shared memory

system we saw that the communication

took place by sharing a region of memory

between the two processes but in this

message passing system we are not going

to share any region of memory but we are

going to have a communication between

two or more processes without sharing

any address space

and why is this useful this is useful in

a distributed environment so for example

let's say that the processes that wants

to communicate they lie within the same

system suppose two processes within the

same system wants to communicate then it

is easy for them to create a shared

region of memory which is a shared

memory and they can communicate using

that shared region of memory so as we

already studied the shared memory it

lies in the address space of one of the

processes and both the processes that

wants to communicate needs to be able to

access that region of shared memory but

think of a scenario in which you have a

distributed environment or a

communication process that resides on

computers connected by a network so for

this let us take the example of internet

chat so let's say that you are chatting

with your friend over the internet so

you are sending message from your system

and your friend is receiving the

message in his system that is located

somewhere else

so even in this place the two processes

needs to communicate your process from

your system and the process in your

friend system also needs to communicate

but they are not residing in the same

system but they are residing in

different systems connected through a

network so in this scenario it is

difficult to create a region of shared

memory that can be accessed by these two

processes so in this kind of scenario

message passing system can be used where

the communicating processes will

communicate via some kind of messages

which will be sent from one process to

another process so in this way they

don't need to have a region of shared

memory but they can send messages to

another process and also it can receive

messages from other processes so that is

how message passing systems work so

we'll go into the details of message

passing systems and we will see what are

his features and how does this message

passing system actually work so the

message passing facility provides at

least two operations which are send

message and receive message so these are

the two operations provided by a message

passing facility the first one is send

message so from the name itself it is

understood that send message is the

operation that allows the process to

send the message to the other process to

which it wants to communicate and then

we have the receive message operation so

the receive message operation

is the operation which allows the

process which is the recipient of the

message to receive the message from the

other process that is sending the

message

so these are the two operations that we

have in a message passing facility and

then

message sent by a process can be of

either fixed or variable length so when

the message is being sent from one

process to another process

the length of the message or the size of

the message can be either of fixed size

or variable size so fixed size means the

message will have a particular size that

will be fixed and it cannot exceed that

size and variable size means the size of

the message can vary it can be big or it

can be small so let us see what are the

features of these fixed size messages

and variables as messages and how easy

is it to implement these two kind of

message sizes so in fixed size the

system level implementation is

straightforward

but

makes the task of programming more

difficult now why do we say this in

fixed size it says that the system level

implementation is straightforward it

says so because if you are going to

implement a fixed size system the system

level implementation is easy or it is

not very difficult because when you are

designing your system you have to design

your system in such a way that the

length of the messages that will be sent

by the processes will be of fixed size

so in that way the implementation is

straightforward so the system level

implementation that means the way in

which the system is implemented is

straightforward and easy because you

just have to maintain a fixed size

but it makes a task of programming more

difficult now the task of programming

becomes more difficult now what is the

task of programming so when you are

programming you may have to control the

way in which the messages are sent from

one process to another but you have to

always keep in mind that the size of the

message should be fixed you cannot vary

your

size of the message so sometimes when

you are programming you may want to have

messages of larger sizes but it is not

possible because we are only allowed to

have messages of fixed size so that is

why it says the task of programming

becomes more difficult in this fixed

size method now coming to the variable

size it requires a more complex system

level implementation but the programming

task becomes simpler so in case of

variable size messages it requires a

more complex system level implementation

which means that when you are designing

the system it may be a little more

complex or it may be a little more

difficult because you have to allow the

messages to be of any size or variable

size the size should be allowed to vary

so when you are designing something of

that form the messages should be allowed

to take any size they may be bigger size

or smaller size and it must be versatile

in that way so the system level

implementation becomes more complex but

the programming task becomes simpler but

in this case the programming task

becomes simpler because when you are

programming it is easy for you because

you are not having a restriction on the

size of the messages so if you want to

program something controlling the

communication between two processes then

it is easy because you don't have to

worry about the size of the message that

has to be sent it can be of any size so

the programming task becomes simpler so

those are the

two kinds of message sizes that we have

fixed and variable size

now if process p and q wants to

communicate they must send messages to

and receive messages from each other so

let's say that we have two processes p

and q that wants to communicate so if

they want to communicate then they must

send messages to and receive messages

from each other p and q must be able to

send messages to each other and p and q

also must be able to receive messages

from each other now how can we

facilitate this so in order to make this

happen a communication link must exist

between them so there must be a

communication link between the process p

and process q so that they can have

communication with each other so unlike

shared memory in which the communication

took place by writing into a region of

shared memory and reading from the

region of shared memory so in case of

message passing system we must have a

communication link between the two

processes that wants to communicate

so how do we implement this

communication link so this link can be

implemented in a variety of ways there

are several methods for logically

implementing a link and the send

and receive operations like the ones

given below so here we are concerned

about the ways for logically

implementing a link we are not concerned

about how to physically implement the

link so the way in which the link can be

physically implemented will be discussed

in another chapter later on but we are

concerned about how can we logically

implement this link between the two

processes that wants to communicate and

send the messages to each other

so it says here that we have several

methods for implementing this link and

the send and receive operations we have

already discussed the send and receive

operations so for implementing this

there are several methods like the ones

given below

like direct or indirect communication

synchronous or asynchronous

communication

automatic or explicit buffering and

there are several issues related with

features like naming synchronization and

buffering so these are the methods we

have in which we can logically implement

a link so that the processors can

communicate to each other and there are

several issues associated with these

features which are given here like

naming synchronization and buffering so

this part which is the methods for

logically implementing a link and the

issues associated with these features

like naming synchronization and

buffering will be discussed in the

second part of this lecture so i hope

this first part of message passing

systems are clear to you thank you for

watching and see you in the next one

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[Applause]

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