From: Paul Brannan <pbrannan@...>
Date: 2008-03-25T00:43:07+09:00
Subject: Re: Thread#raise, Thread#kill, and timeout.rb are unsafe

On Thu, Mar 20, 2008 at 07:21:06AM +0900, MenTaLguY wrote:
> Now, the question with IO and asynchronous exceptions in Ruby is
> whether there is a good way to report a partial result?

The existing API already returns the number of bytes successfully
written for both IO#write and IO#syswrite.  But how do we find out what
caused the operation to be interrupted?  Currently IO#write gives an
exception:

irb(main):001:0> r, w = IO.pipe
=> [#<IO:0x4039f734>, #<IO:0x4039f70c>]
irb(main):002:0> t = Thread.new { w.write("HELLO" * 20000) }
=> #<Thread:0x4039a0a4 run>
irb(main):003:0> r.close
=> nil
irb(main):004:0> t.join
Errno::EPIPE: Broken pipe
        from (irb):2:in `write'
        from (irb):4:in `join'
        from (irb):4

and IO#syswrite gives the number of bytes written:

irb(main):018:0> sock = TCPSocket.new('localhost', 2000)
=> #<TCPSocket:0x4043bf1c>
irb(main):019:0> t = Thread.new { p sock.syswrite("HELLO" * 200000) }
=> #<Thread:0x40428804 run>
irb(main):024:0> t.join
131072
=> #<Thread:0x4040d324 dead>

I think the behavior of IO#syswrite is correct (because there is only
one write(2) system call), but IO#write actually got *both* partial
success *and* an exceptional condition, so what should its behavior be?

Paul