[ruby-core:90255] [Ruby trunk Bug#15367] IO.select is not resumed when io-object gets closed

[melentievm@gmail.com]

Issue #15367 has been updated by printercu (Max Melentiev).


I'm using `IO.select` with ssl socket as it's suggested in docs https://ruby-doc.org/core-2.5.3/IO.html#method-c-select :

~~~ruby
    def read_from_socket
      socket.read_nonblock(read_buffer_size)
    rescue IO::WaitReadable
      IO.select([socket.to_io])
      retry
    rescue IO::WaitWritable
      IO.select(nil, [socket.to_io])
      retry
    end
~~~

Other code is like this (simplified):

~~~ruby

def run
  loop do
    data = read_from_socket
    process(data)
  end
rescue Errno::EBADF, IOError
  raise unless @stopped
end

def stop
  @stopped = true
  socket.close
end

Signal.trap('TERM') { Thread.new { stop } } # thread is just workaround for trap contex
run
# exit
~~~

I can't use just `Thread#kill` to not stop thread while it runs `#process`.
It works fine on macOS because `socket.close` makes read_from_socket fail with Errno::EBADF which is rescued later.
However this does not work on linux and `#run` hangs forever.

Is there a right way for this task to not face multi-thread limitations of `IO.select`?

For now I use workaround:

~~~ruby
    SELECT_TIMEOUT = 10

    def read_from_socket
      socket.read_nonblock(read_buffer_size)
    rescue IO::WaitReadable
      nil until IO.select([socket.to_io], nil, nil, SELECT_TIMEOUT)
      retry
    rescue IO::WaitWritable
      nil until IO.select(nil, [socket.to_io], nil, SELECT_TIMEOUT)
      retry
    end
~~~

----------------------------------------
Bug #15367: IO.select is not resumed when io-object gets closed
https://bugs.ruby-lang.org/issues/15367#change-75372

* Author: printercu (Max Melentiev)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Here is sample code:

~~~ ruby
rp, wp = IO.pipe
t2 = Thread.new { IO.select([rp]) }
# This also does not work:
# t2 = Thread.new { IO.select([rp], nil, [rp]) }
sleep 0.01
rp.close
t2
# => #<Thread:0x00000000089b6ce0@(pry):51 sleep>
~~~

It happens only on linux, tested with 2.5.1, 2.6.0-preview2. On macOS it gives error, as expected:
~~~
#<Thread:0x00007fab3aebce58@(pry):5 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
	1: from (pry):5:in `block in <main>'
(pry):5:in `select': Bad file descriptor (Errno::EBADF)
> t2
=> #<Thread:0x00007fab3aebce58@(pry):5 dead>
~~~



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