From: Yohanes Santoso <ysantoso@...>
Date: 2002-03-13T10:18:57+09:00
Subject: Re: gzip again...

Dave Thomas <Dave@PragmaticProgrammer.com> writes:

> 
> You're writing 100k in one chunk. gzip starts reading it, and after
> reading 50k it has enough data to start writing some output. Perhaps
> it has 200k to write to you. However, you're still busy writing, and
> don't yet have a read pending, so gzip will be suspended. The result
> is that both sides will be deadlocked.

This is why you cannot use IO.popen without setting O_NONBLOCK. You
got to either use popen3 and select, or thread, although I doubt
thread will work if you dont set O_NONBLOCK to the pipe returned by
IO.popen. 

Since I don't know how to pass O_NONBLOCK to IO.fcntl, then the
following is an implementation using the popen3&select method, which
may or may not work. May require some tweaking to get it working. I
don't have ruby here. 

It's not very efficient, working a byte at a time, but I see no
alternatives without O_NONBLOCK. If it had been writting even two
bytes at a time, there is no guarantee that the IO won't block while
writting the second byte. So conclusion is, yeah, you need O_NONBLOCK.

Does someone know how to use O_NONBLOCK in IO.fcntl?

data = File.open('blabala.gz') {|f| f.read}
File.open("/tmp/test.out", "w") { |file|
  dataWhere = 0
  popen3("gzip -dc") { |ios|
    i,o,e = ios
    while ready = select([o],[i]) do
      if ready[0].length > 0 then file.write(ready[0][0].getc) end
      if ready[1].length > 0 and dataWhere <= data.length 
	  ready[1][0].putc(data[dataWhere])
          dataWhere+=1
      end
    end
  }
}


YS.