From: Robert Klemme <shortcutter@...>
Date: 2009-01-19T19:18:52+09:00
Subject: Re: Thread starvation

2009/1/19 Jakub Pavlík jn. <severus@post.cz>:
>> On 18.01.2009 19:04, Jakub Pavlík jn. wrote:
>> >Hello,
>> >
>> >In my game freeVikings [http://freevikings.sf.net] I have code listed
>> >below.
>> >It uses threads and sometimes problem known as "thread starvation" occurs.
>> >Does anyone know some solution?
>> >(A more detailed description is under the code listing.)
>> >
>> >----------------------------------
>> >def do_loading(&block)
>> >  Thread.abort_on_exception = true
>> >
>> >  load_t = Thread.new {
>> >    Thread.current.priority = 1
>> >    Thread.stop
>> >
>> >    block.call
>> >  }
>> >
>> >  progressbar_t = Thread.new {
>> >    Thread.current.priority = 2
>> >    load_t.run
>> >
>> >    loop {
>> >      paint_loading_screen @app_window, true
>> >      sleep 0.3
>> >    }
>> >  }
>> >
>> >  load_t.join
>> >  Thread.kill progressbar_t
>> >end
>> >----------------------------------
>> >
>> >It's an instance method of class Game and is used in this way:
>> >a_game.do_loading {
>> >  # load something here
>> >}
>> >
>> >Purpose of this method is to show a simple progressbar while doing some
>> >long-lasting operation (e.g. loading new level).
>> >
>> >It creates two threads: load_t, in which given block is executed
>> >and progressbar_t, which regularly calls Game#paint_loading_screen
>> >(method, which repaints loading screen with progressbar).
>> >
>> >Thread progressbar_t has higher priority, because I need it to be called
>> >often and not to e.g. wait for load_t's end.
>> >
>> >Unfortunatelly from time to time Thread load_t is somehow "suspended" -
>> >progressbar shows progress on and on, but nothing happens.
>> >I think it's a case of so called "thread starvation" and would be very glad
>> >to know how to avoid it.
>>
>> I guess this depends on what you do in "block".  It's difficult to
>> analyze this without having all the information...
>>
>> Can you provide more detail?
>
> Method do_loading is used for two purposes:
> 1. loading of a world:
>   code in the block goes through a tree of directories and in each reads
>   a XML file
> 2. loading of a level:
>   two XML files (level description & map data created in Tiled) +
>   one ruby script (which often requires many others) are loaded from a
>   given directory, many graphics are loaded and huge SDL surfaces are built
>
> Thread starvation usually occurs in the second case.

This is still pretty vague IMHO.  Did you try to trace execution via
set_trace_func?  That might help.

Cheers

robert


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