Re: Are there real use cases with the Java access modes?

Program Mistake Detector (PMD) is an awesome tool for finding many
mistakes.  It can be easily improved with new rules.  There are other
similar tools out there as well but I am not sure of their capabilities.

Consider this simple case...

private boolean m_quit;   // not volatile

while (!m_quit)
{
   // do some things
}

If the loop body does not modify m_quit, then we can write a PMD rule to
flag this as an unintended infinite loop (i.e. a mistake).  If the while
loop has no method calls, then this simple case can be done with a very
simple PMD rule.  If the while loop calls other methods, then the PMD rule
will need to explore the call tree to see if m_quit is modified.  This will
be more complex to write.

With such a rule in place, when a programmer writes an unintended infinite
loop, then PMD will flag the problem.  The programmer can then fix the
problem and the bug will only exist for a few minutes on the programmer's
machine.

With such a simple solution (e.g. create a PMD rule), I would rather
improve linters to catch programmer's mistakes than make a change to Java
that could hurt performance.

On Mon, Jul 19, 2021 at 8:26 AM Andrew Haley via Concurrency-interest <
[email protected]> wrote:

> On 7/19/21 3:06 PM, Gregg Wonderly via Concurrency-interest wrote:
> > I am specifically against the single optimization I illustrated that
> rewrites code to be non-logically executed, without the user being aware of
> this happening and not being warned that an optimization has potentially
> made the logic of the application not work as expected.
>
> That single optimization is no more than hoisting a memory load. It's
> one of the most common optimizations there is. It probably happens
> many times in every moderately complex method. It's not some kind of
> weird "let's turn this into an infinite loop" optimization.
>
> For every non-volatile field load, in the absence of synchronization
> actions, it is entirely correct and proper to hoist the result of that
> load into a register, or propagate its value some other way. This is
> common in many programming language implementations, and is not going
> to change. It is a very important optimization.
>
> --
> Andrew Haley  (he/him)
> Java Platform Lead Engineer
> Red Hat UK Ltd. <https://www.redhat.com>
> https://keybase.io/andrewhaley
> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
>
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