[Haskell-cafe] Re: Cleaning up threads
marlowsd at gmail.com
Wed Sep 22 04:21:57 EDT 2010
On 22/09/2010 02:18, Mitar wrote:
> On Tue, Sep 21, 2010 at 11:10 PM, Simon Marlow<marlowsd at gmail.com> wrote:
>> So rather than admitting defeat here I'd like to see it become the norm to
>> write async-exception-safe code.
> This is also what I think. You have to make your code work with
> exceptions, because they will come sooner or later. So if you handle
> them properly, once you have this implemented, then you can easily use
> them also for your own stuff.
>> It's not that hard, especially with the new mask API coming in GHC 7.0.
> Not hard? I see it almost impossible without mask. You cannot have
> arbitrary long cleanup functions in for example bracket because
> somebody can (and will) interrupt it even if you block, because some
> function somewhere deep bellow will unblock.
mask doesn't save you from this, because a function in a library below
you might perform an interruptible operation like takeMVar, and that
operation could receive another asynchronous exception. You could use
maskUninterruptible, but that's not a good solution either - if an
operation during cleanup really does block, you'd like to be able to
Control-C your way out.
So the only way out of this hole is: don't write long cleanup code that
needs to mask exceptions. Find another way to do it.
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