From: Tanaka Akira <akr@...17n.org>
Date: 2004-07-22T16:01:06+09:00
Subject: Re: sysread and buffered I/O

In article <opsbhnakfau5o8pp@233.dallas-20rh16rt.tx.dial-access.att.net>,
  "John Feezell" <JohnFeezell@3wplace.com> writes:

> Here are some other possible names that seems to fit with readchar,  
> readline,
> and readlines and yet catch the idea of "readpartial."
>
> readportion
> readparcel
> readbundle
> readatmost
>
> Personally, "readatmost" would fit closes in my mind to the above  
> description.

"at most" doesn't represent the difference between IO#readpartial and
IO#read.  IO#read also reads at most <i>integer</i> bytes from the I/O
stream.

The difference is the blocking behaviour.

% (sleep 1; echo abc; sleep 1; echo def) | ./ruby -e 't1 = Time.now; p STDIN.readpartial(4096); t2 = Time.now; p t2-t1'
"abc\n"
1.001541
% (sleep 1; echo abc; sleep 1; echo def) | ./ruby -e 't1 = Time.now; p STDIN.read(4096); t2 = Time.now; p t2-t1'
"abc\ndef\n"
2.011527

Both IO#readpartial and IO#read blocks until some data are available.
But after some data are avalable, IO#readpartial just return the data
and doesn't block anymore.  IO#read blocks until EOF or specified
length, though.
-- 
Tanaka Akira