From: Michael Malone <michael.malone@...>
Date: 2009-03-16T07:02:39+09:00
Subject: does IO.read block?

Hi All,

I have a setup where I am writing to a pipe in one process and reading 
in another.  I am closing the end I'm not using etc, but I have a new 
problem.  Having recently read that I was just getting lucky when it 
came to my IO.write completing each time (probably due to Ruby's green 
thread implementation in v1.8 and 'nice' scheduling) but now that the OS 
has taken over scheduling, it tends to interrupt things when it damn 
well feels like it, so I believe some of my write calls aren't 
completing, so I've set up a loop like this:

rescue Exception => error
  ex_string = Marshal.dump(error)
  ex_size = ex_string.bytesize
  bytes_written = 0
  while bytes_written < ex_size
    bytes_written += write_end.write(ex_string.slice!(bytes_written))
  end
  ensure
    write_end.close
  end
end

and in the other process, I currently make just one call to 
read_end.read() so my question is, is this guaranteed to get all of the 
bytes written through multiple calls to write or do I need to set up a 
similar loop on the read end?  like

while !(read_end.eof?)
    string += read_end.read
end

Or does read_end.read block until it finds EOF?

Can anyone tell me what happens when read_end.read is re-scheduled 
partway through?  Or is that guaranteed to finish?
I'm running this in Linux, so posix rules probably apply.

Thanks in advance,
Michael

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