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Interprocess Communication: Message Passing and UNIX Pipes, Study notes of Operating Systems

Villanova UniversityOperating Systems

Interprocess communication (ipc) through message passing and unix pipes. It covers various message passing techniques, including synchronous and asynchronous methods, and discusses the use of mailboxes. The document also provides a case study on ipc in unix, focusing on pipes and their creation, file descriptors, and inheritance in parent-child relationships.

Typology: Study notes

Pre 2010

Uploaded on 08/13/2009

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New Topic: Interprocess Communication
•Shared data structures offer only an unstructured method of
IPC
•Alternative: processes can communicate by exchanging
“messages”
–“message” can be simply a data value
–no need for shared variables (or their headaches)
•Analogy: global variables vs. parameter passing to
subroutines in a high-level language
•Basic operations: send(message) & receive(message)
Basic Message-Passing Issues
•How are communication links established?
•Any reliability measures?
•How many processes can be associated with a link?
•How many messages can be buffered at once in the link?
•What are message sizes?
•How are communication links closed, or deleted?
1
pf3
pf4
pf5

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Download Interprocess Communication: Message Passing and UNIX Pipes and more Study notes Operating Systems in PDF only on Docsity!

New Topic: Interprocess Communication

• Shared data structures offer only an unstructured method of

IPC

• Alternative: processes can communicate by exchanging

“messages”

– “message” can be simply a data value

– no need for shared variables (or their headaches)

• Analogy: global variables vs. parameter passing to

subroutines in a high-level language

• Basic operations: send(message) & receive(message)

Basic Message-Passing Issues

• How are communication links established?

• Any reliability measures?

• How many processes can be associated with a link?

• How many messages can be buffered at once in the link?

• What are message sizes?

• How are communication links closed, or deleted?

Message-Passing Varieties

• Synchronous (Blocking)

• Asynchronous (Non-Blocking)

• Symmetric Direct

• Asymmetric Direct

• Indirect IPC (Mailboxes)

Synchronous vs. Asynchronous

• Synchronous:

– Sender’s processing progress is blocked until an ACK is received from

receiver.

– Receiver’s processing progress is blocked until it receives some message

from sender.

• Asynchronous:

– Sender does not wait for ACK from receiver

– Receiver simply continues processing if no message has been sent

Indirect IPC

• Messages are sent from a sender to a mailbox (buffer),

where they are held until a receiver reads one.

– you don’t need to know a process’ name to communicate, only need to

know MAILBOX where it gets its messages!

• Mailbox operations:

– send

– receive

– create

– destroy

• Mailbox lifetimes:

– “Immortal:” some owned by system, having a fixed name, and are never

destroyed

– others might be dynamically created, named, and destroyed by any process

Case Study: IPC in UNIX(tm)

• Processes in UNIX communicate via PIPES

• Pipes have a “read end” and a “write end”

P1 Pipe_ID P

write(pipe_id, message, nbytes) (^) read(pipe_id,buffer,xbytes)

Pipes are created via the “pipe()” system call

int p[2]; ... ... pipe(p); / creates a pipe and returns ID of read-end in p[0] and ID of write-end in p[1] /

Pipe creation

Pipes are created via the “pipe()” system call

int p[2]; ... ... pipe(p); / creates a pipe and returns ID of read-end in p[0] and ID of write-end in p[1] /

When a process creates a pipe, it is given EXCLUSIVE

access to the pipe’s read and write ends.

- all this does is let process want “talk to itself”

- how might this be useful?

File Descriptors & Pipes in UNIX

• Feature: file system, device i/o and IPC are integrated in

UNIX!

• Each process has a list (where?) of (typically 16) file (object)

descriptors

• Each open descriptor is associated with a device, file, or

pipe

• “write(, , )”

– outputs the buffer to the file, pipe, or device associated with the

Pipes, Parents, and Progeny in Unix

p[1] p[0]

Step 2: P0 creates P1 and P2, which inherit pipes

At this time, any of them can read/write from/to the pipe.

P

P

P

Pipes, Parents, and Progeny in Unix

P

p[1] p[0]

P

Step 3: all processes close pipe ends which they will not (should not) be accessing:

close(p[0]); close(p[1]);

close(p[1]);

close(p[0])

P

P

P