[racket] DrRacket locking up on errors in non-GUI worker threads

From: Neil Toronto (neil.toronto at gmail.com)
Date: Wed Aug 24 18:56:20 EDT 2011

Right. I've also just found thread-send, which doesn't block, and is a 
lot more convenient than managing my own channels.

On 08/24/2011 04:48 PM, Jay McCarthy wrote:
> async-channel-put is the one that doesn't block
> Sent from my iPhone
> On 2011/08/24, at 16:42, Neil Toronto<neil.toronto at gmail.com>  wrote:
>> Oh! I've been laboring under the delusion that channel-put doesn't block, only channel-get. That would explain a lot.
>> I'll try some of this kill safety stuff. Where's the paper?
>> Neil T
>> On 08/24/2011 03:47 PM, Robby Findler wrote:
>>> It seems like the exception stops the render-thread from doing a
>>> channel-get so the channel-put that drracket does blocks forever.
>>> Right?
>>> Have you read the kill safety paper? I think that you'd need to use a
>>> pattern like that to make this really work. After all, the user's
>>> program can be terminated at any time and the repl might still contain
>>> those snips that are trying to draw themselves without someone to talk
>>> to on the other side.
>>> Assuming you've read that paper, then I think the thing you want to do
>>> is set up a thread that just listens for requests for user-side state
>>> and answers them. This thread will be on the user's thread and subject
>>> to random killing (so use the kill safety stuff to deal with that).
>>> Then, do everything else on the DrRacket side where you're safe from
>>> killing.
>>> Robby
>>> On Wed, Aug 24, 2011 at 4:27 PM, Neil Toronto<neil.toronto at gmail.com>   wrote:
>>>> I can't keep DrRacket from locking up whenever an exception is raised on a
>>>> non-GUI thread that does work in response to a channel-put from the GUI
>>>> thread.
>>>> I've attached simplified code for a custom snip% and its non-GUI render
>>>> thread. The code contains commented-out attempts at solving the lock-up
>>>> problem and comments underneath that say what the solutions actually did.
>>>> Details:
>>>> I've got a descendant of image-snip% that needs to be updated periodically.
>>>> Rendering the update depends on a zillion parameters, which I MUST get from
>>>> the program thread, not the GUI thread. If I got parameters from the GUI
>>>> thread, setting parameters in the program thread before creating the snip
>>>> wouldn't affect later rendering, which would be bad.
>>>> To ensure that rendering uses parameters from the program thread, I start a
>>>> rendering thread upon creating the snip. The rendering thread inherits the
>>>> program thread's current parameters.
>>>> When the snip updates, it uses channel-put on the GUI thread to tell the
>>>> rendering thread to render. When the rendering thread finishes, it uses
>>>> channel-put to return the result.
>>>> When the snip is copied, the copy needs a new rendering thread. I have the
>>>> old rendering thread create a new rendering thread for the copy. The new
>>>> thread's parameters are what the program thread's parameters were when the
>>>> original snip was created.
>>>> This all works just great, no problems.
>>>> Until there's an error. Then I can't keep this silly tower of threads from
>>>> locking up DrRacket, even if I catch the errors and silently ignore them!
>>>> Help, please?
>>>> Neil T
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