Re: Draft of generation 2 thread class

From: Tom Becker (voidampersand_at_[hidden])
Date: 2002-01-24 13:19:00

Thu, 24 Jan 2002 14:55:51 -0000, "bill_kempf" <williamkempf_at_[hidden]> wrote:
>--- In boost_at_y..., "davlet_panech" <davlet_panech_at_y...> wrote:
>  > in addition to check_cancelled(). I think having a way to determine
>>  the cancellation state of a thread with a simple test (as opposed
>to
>>  an exception) could come in handy in some situations:
>>
>  >   while( !cur.is_cancelled() ) {
>  >     // do somtheing
>>    }
>>    // do some other thing
>>
>>  as opposed to
>>
>>    try {
>>      while( true ) {
>>        // do something
>>      }
>>    catch( thread_cancel & ) {
>>      // do some other thing
>>    }
>
>I'd like to hear some other people's opinion on this one.  My first
>reaction is that this won't really serve any useful purpose and can
>actually lead to poor coding practices, but I've formed bad opinions
>in this area before.  So, I'd like to hear other people's thoughts.

I agree.

The first example probably won't work as expected. The call to 
is_cancelled() might actually catch a cancellation if the request 
comes in after the last cancellation point in "do something". If the 
timing is different, the exception will bypass it, and "do some other 
thing" will never happen. The first example is not equivalent to the 
second.

The second example violates the "exceptions should be used only in 
exceptional circumstances" rule. The thread should be written so 
there's a gentle way to ask it to stop.

     while (!done()) {
         // do something
     }

Regards,

   Tom

-- 
Tom Becker                      "Within C++, there is a much smaller and
<voidampersand_at_[hidden]>        cleaner language struggling to get out."
                                                       -- Bjarne Stroustrup