RE: A java DEBUG flag

[Boehm, Hans]

I'm still not sure how to do this cleanly.  The problem is not factoring out
the assertion checking code.  It's that you want to maintain e.g. a counter
only if debugging is enabled.  Thus you want to conditionally execute
something with a side-effect, where the condition is evaluated at compile
time.  Expressions in assertions aren't supposed to have side-effects
(though I guess that isn't enforced).  There doesn't seem to be another way
to condition something on whether assertions are enabled.

You could maintain the added state unconditionally, and hope that the
compiler recognizes it as dead code if debugging is disabled.  But that's
often not very realistic.  For example, if I look at some of the code in the
GC that's covered by #ifdef GC_ASSERTIONS, much of it is already hard to
prove dead with assertions disabled, and it would be still harder if you had
to preserve null pointer exceptions. 

Hans

> -----Original Message-----
> From: Cedric Berger [mailto:address@hidden
> Sent: Friday, December 29, 2000 10:31 AM
> To: Boehm, Hans
> Cc: 'address@hidden'; Brian Jones;
> address@hidden; address@hidden
> Subject: Re: A java DEBUG flag
> 
> 
> 
> "Boehm, Hans" wrote:
> > 
> > > This is in the SUN Assertion JSR.
> > > http://java.sun.com/aboutJava/communityprocess/jsr/asrt_prop.html
> > >
> > > ... The documentation is public but we certainly can not
> > > participate in its
> > > development because of SUNs *stupid* IP restrictions in the
> > > JCP.  There are good
> > > ideas here though and since this stuff will eventually make
> > > it into JDK 1.4 I
> > > would say it should eventually belong here.
> > >
> > True.  But isn't this an awfully weak proposal?  It doesn't 
> seem to allow me
> > to cleanly compute additional state that's used only in 
> assertion checking.
> > I find that I need to do that all the time in order to be 
> able to write
> > reasonable assertions.  For example, I might explicitly 
> keep track of who
> > holds a particular lock, so that I can assert that I hold 
> it at some point.
> > Or I might need to count opened files so that I can assert 
> that I closed
> > everything I opened in a certain section of code.  Or ...
> > 
> > Hans
> 
> Can't you put all this stuff a special debug class to keep 
> things clean?
> This class will only gets loaded if assertions are enabled!
> 
> class Debugging {
>     static int openFilesCount;
>     static boolean openFile() {
>         return openFilesCount < LIMIT;
>     }
>     static boolean closeFile() {
>         return openFilesCount > 0;
>     }
> }
> class Main {
>     void doSomething() {
>         assert(Debugging.openFile());       
>         // do something
>         assert(Debugging.closeFile());
>     }
> }
> 
> Cedric
>