unix_server: fix for infinite loop

Occasionally, killing a sink from an external process could result in an
infinite loop due to the lack of close notification from __dst_error (in
DTAS::Buffer) up to the top-level event loop.  Since it is not easy to
notify the top-level event loop, we'll detect closed IOs after-the-fact
and retry as needed in a cold rescue path.

This fixes an occasional error (usually when using a non-parallel make)
in the test suite:

TestPlayerIntegration#test_sink_killed_during_play:
Timeout::Error: execution expired
    $HOME/dtas/test/player_integration.rb:57:in `sleep'
    $HOME/dtas/test/player_integration.rb:57:in `block in wait_pid_dead'
    $HOME/$RUBY/lib/ruby/2.2.0/timeout.rb:91:in `block in timeout'
    $HOME/$RUBY/lib/ruby/2.2.0/timeout.rb:35:in `block in catch'
    $HOME/$RUBY/lib/ruby/2.2.0/timeout.rb:35:in `catch'
    $HOME/$RUBY/lib/ruby/2.2.0/timeout.rb:35:in `catch'
    $HOME/$RUBY/lib/ruby/2.2.0/timeout.rb:106:in `timeout'
    $HOME/dtas/test/player_integration.rb:54:in `wait_pid_dead'
    test/test_player_integration.rb:42:in `test_sink_killed_during_play'

0 files changed, 0 insertions, 0 deletions