From: Yusuke ENDOH <mame@...>
Date: 2011-01-18T23:04:08+09:00
Subject: [ruby-core:34555] Re: [Ruby 1.9-Bug#4285] Ruby don't have asynchrounous exception safe syntax and It should have.

Hi,

2011/1/18 Motohiro KOSAKI <redmine@ruby-lang.org>:
> Endoh-san, Grr, my fault. I thought Thread.join call pthread_join, but it doesn't.

I thought so :-)


> But generically, Asynchrounous exception during OS resource handler class construction is still dangerous. new example is here.
>
>  def foo
>    begin
>      f = open("example-file")
>    ensure
>      f.close
>  end
>
>  timeout (1) {
>     foo
>  }
>
> if assignment of f was lost, we have no way to close f.

Yes.  Surely, the current Thread#raise is dangerous.


> I still propose language enhancemnet for any async exception for 2.0.

Basically agreed, but what is needed actually?
I guess that we need these three features, including a semantics
change.

  - a feature to block async exception

    t = Thread.new do
      # exception may be raised
      block_async_exc do
        # exception may NOT be raised
      end
      # exception may be raised
    end
    t.raise

  - a feature to allow async exception

    t = Thread.new do
      # exception may be raised
      block_async_exc do
        # exception may NOT be raised
        allow_async_exc do
          # exception may BE raised
        end
        # exception may NOT be raised
      end
      # exception may be raised
    end
    t.raise

  - async exception is blocked by default in rescue clauses and
    ensure clauses

    t = Thread.new do
      begin
        # exception may be raised
      ensure
        # exception may NOT be raised
        allow_async_exc do
          # exception may BE raised
        end
      end
      # exception may be raised
    end
    t.raise

I remember that we discuss this topic with akr informally, but I forgot
the conclusion...

-- 
Yusuke Endoh <mame@tsg.ne.jp>