Simulating RUBY_CRITICAL

Hi all,

I've added some critical section methods to the
Windows::Synchronize 
module in the windows-pr library (in CVS). Looking at the
RUBY_CRITICAL 
macro from rubysig.h, it basically looks like this (in pure
Ruby):

def RUBY_CRITICAL(&block)
    critical_section = [0].pack('L')
    InitializeCriticalSection(critical_section)
    EnterCriticalSection(critical_section)
    block.call
    LeaveCriticalSection(critical_section)
end

But, shouldn't we ensure that we leave the critical section
once 
entered, like so?

# This is what's currently in CVS
def RUBY_CRITICAL(&block)
    critical_section = [0].pack('L')
    begin
       InitializeCriticalSection(critical_section)
       EnterCriticalSection(critical_section)
       block.call
    ensure
       LeaveCriticalSection(critical_section)
    end
end

Or, am I worrying over nothing?

Regards,

Dan
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Hi Dan,

I certainly like the idea of ensuring that we leave the
critical
section once entered.  However, there are some possible
complications.
 For example, MSDN says:

"Windows 2000/NT:  In low memory situations,
EnterCriticalSection can
raise an exception. Do not attempt to handle this exception;
instead,
either terminate the process or allow the exception to pass
to the
unhandled exception filter. To avoid an exception due to low
memory,
call the InitializeCriticalSectionAndSpinCount function to
preallocate
the event used by EnterCriticalSection instead of calling
the
InitializeCriticalSection function, which forces
EnterCriticalSection
to allocate the event. Preallocating the event is not
necessary on
Windows XP or later because EnterCriticalSection is
guaranteed not to
fail due to lack of resources."
http://msdn2.microsoft.com/en-us/library/ms682608.aspx


Then again, I don't think it's too likely that we'd be low
enough on
memory for EnterCriticalSection to fail.

Best regards,

Wayne

On 10/20/07, Daniel Berger <djberg96gmail.com> wrote:
> Hi all,
>
> I've added some critical section methods to the
Windows::Synchronize
> module in the windows-pr library (in CVS). Looking at
the RUBY_CRITICAL
> macro from rubysig.h, it basically looks like this (in
pure Ruby):
>
> def RUBY_CRITICAL(&block)
>     critical_section = [0].pack('L')
>     InitializeCriticalSection(critical_section)
>     EnterCriticalSection(critical_section)
>     block.call
>     LeaveCriticalSection(critical_section)
> end
>
> But, shouldn't we ensure that we leave the critical
section once
> entered, like so?
>
> # This is what's currently in CVS
> def RUBY_CRITICAL(&block)
>     critical_section = [0].pack('L')
>     begin
>        InitializeCriticalSection(critical_section)
>        EnterCriticalSection(critical_section)
>        block.call
>     ensure
>        LeaveCriticalSection(critical_section)
>     end
> end
>
> Or, am I worrying over nothing?
>
> Regards,
>
> Dan
> _______________________________________________
> win32utils-devel mailing list
> win32utils-develrubyforge.org
> http://rubyforge.org/mailman/listinfo/win32utils-devel

>
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Wayne Vucenic wrote:
> Hi Dan,
> 
> I certainly like the idea of ensuring that we leave the
critical
> section once entered.  However, there are some possible
complications.
>  For example, MSDN says:
> 
> "Windows 2000/NT:  In low memory situations,
EnterCriticalSection can
> raise an exception. Do not attempt to handle this
exception; instead,
> either terminate the process or allow the exception to
pass to the
> unhandled exception filter. To avoid an exception due
to low memory,
> call the InitializeCriticalSectionAndSpinCount function
to preallocate
> the event used by EnterCriticalSection instead of
calling the
> InitializeCriticalSection function, which forces
EnterCriticalSection
> to allocate the event. Preallocating the event is not
necessary on
> Windows XP or later because EnterCriticalSection is
guaranteed not to
> fail due to lack of resources."
> http://msdn2.microsoft.com/en-us/library/ms682608.aspx

> 
> Then again, I don't think it's too likely that we'd be
low enough on
> memory for EnterCriticalSection to fail.

<snip>

Hi Wayne,

Yeah, I saw that. I guess I'm not especially worried about
checking for 
low memory for two reasons. First, it seems we don't have to
worry about 
it with XP and later, which covers the majority of Windows
users at this 
point I think. Second, I'm pretty sure the interpreter would
die anyway 
if there were a memory allocation issue.

But, now that I look at this code, I'm somewhat confused as
to why they 
felt compelled to wrap methods like Dir.mkdir in a
RUBY_CRITICAL block 
in the first place. Are they trying to make it thread safe?
The Ruby 
interpreter isn't thread safe to begin with. Are they trying
to make 
create + chmod a single transaction? Seems overkill, and
besides, the 
code in dir.c takes no such precaution for Unix.

I'd really like to see the use cases for why this was used.

Regards,

Dan
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