Re: [Altosdev-kernel] Ehh.. Streams.. (fwd)

[Alexey M. <tkt...@cs...>]

> Hello, dozzer.
Hei,

> I wonder what's so special about streams? Isn't it just another form
> of what is known as IO control under DOS/Windows? If so, what are
> advantages/disadvantages of the two? Do they have anything to do with
> two channels (command and data ones)? Detailed explanation would be
> nice =) .
No, it is not the same. It is general purpose form of inter process 
communication which can be applied for device drivers and user 
applications. The main difference of stream is that it is demand to 
transfer data with correspondence to specefied binary protocol. The 
control channel transfers commands and data channel transfers raw data. 

You may imagine that stream is the pair of two sockets, but with different 
realization. The control channel needs to transfer small packets of 
control sequences, so it can be realized to be transfered as fast as it 
possible. The data channel can be realized in the common way as a 
common socket.

The adventage of that layout is that we can receive commands and answer to 
it immediately don't waiting for whole data. Then we can receive next 
command even we din't read all data of previous command.

The adventage of using unified form of interprocess communication. You can 
build common application where you send your's graphical representation 
to GUI, read files and write them -- all these you do through streams. The 
program (shell for example) which calls execve and performs your 
application can redirect your streams in any way.. the pepresentation can be 
redirected to machine A and application can be performed on machine B.
If you'll create children processes and communicate with them through 
streams, they can be performed on different machines - and your 
application will know nothing about it.

The streams help to create distributed applications.

Let imaging more sophisticated example. You have machine A and machine B. 
Machine A has no mouse, machine B has two. When you load up drivers, you 
redirect stream from one on machine B to machine A. Now, for all 
applications on machine A mouse will be present. How to realize that in 
kernel - another question.

-- 
See you later,
 d.

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