From: matz@... (Yukihiro Matsumoto)
Date: 2003-03-03T04:16:13+09:00
Subject: Re: Unable to do non-blocking read on socket

Hi,

In message "Re: Unable to do non-blocking read on socket"
    on 03/03/03, Seth Kurtzberg <seth@cql.com> writes:

|>  (a) IO#read (without size) returns all available data on the IO.
|>      It doesn't block if O_NONBLOCK is set.  I was wrong in
|>      [ruby-talk:66149].
|
|Not what I would like to see but not what I was trying to use.

Could you describe "what you'd like to see"?  I'm having (sort of)
hard time to understand you.

By the way, it somewhat different from the documentation:

---------------------------------------------------------------- IO#read
     ios.read( [anInteger] ) -> aString or nil
------------------------------------------------------------------------
     Reads at most anInteger bytes from the I/O stream, or to the end of
     file if anInteger is omitted. Returns nil if called at end of file.
        f = File.new("testfile")
        f.read(16)   #=> "This is line one"

what do you guys think about this behavior.  Should it be fixed as
the document says, or should we update the document?

|>  (b) IO#read (with maximum size) raise an EWOULDBLOCK exception if the
|>      buffer is empty.  It returns the buffer contents if the buffer is
|>      partially filled before EWOULDBLOCK.
|
|It never returns EWOULDBLOCK.  Unless the buffer is empty at the time of the 
|call, it blocks until the maximum number of bytes (as specified by the 
|parameter) is received.
|
|So, both variations block, and NONBLOCK behavior is not available with either.

?

On my machine, ruby 1.8.0 (2003-02-28) [i686-linux], (a) doesn't
block, since it returns as much as data available without blocking if
O_NONBLOCK is set.  And (b) doesn't block neither, since it either
raises the exception, or returns data available on the buffer.

(a) is proved by Nobu's example [ruby-talk:66126].

(b) can be proved by replacing the line in the example

  p s.nonblock {sleep WAIT; s.read}

by

  s.nonblock {sleep WAIT; p s.read(40); p s.read(40)}

and try

  % ruby client.rb foo 2

you'll get

  "hello,"
  /tmp/client.rb:8:in `read': Resource temporarily unavailable - "/tmp/foo" (Errno::EWOULDBLOCK)
          from /tmp/client.rb:8
          from /tmp/client.rb:8:in `nonblock'
          from /tmp/client.rb:8

							matz.