A bit of sugar for j.u.c.locks with try-with-resources?

[David Holmes]

Hi Kris,

On 3/09/2016 12:41 PM, Krystal Mok wrote:
> Hi core-libs developers,
>
> I mostly live down in the VM world, but recently I've been playing with
> j.u.c.locks a bit, and saw that there's an opportunity to retrofit the API
> with the try-with-resources syntax. I wonder if anybody has brought this
> topic up before; apologies if there had been.

Yes brought up a few times. :)

https://dzone.com/articles/project-coin-try-resources

If the syntax is more permissive now then it might be more feasible.

Cheers,
David

> From the JavaDoc of j.u.c.l.ReentrantLock, the following is a typical usage:
>
>  class X {
>    private final ReentrantLock lock = new ReentrantLock();
>    // ...
>
>    public void m() {
>      lock.lock();  // block until condition holds
>      try {
>        // ... method body
>      } finally {
>        lock.unlock()
>      }
>    }
>  }
>
> The try...finally construction really pops out as a try-with-resources
> candidate.
>
> So what if we retrofit that with something like:
>
>  class X {
>    private final ReentrantLock lock = new ReentrantLock();
>    // ...
>
>    public void m() {
>      try (lock.lock()) { // block until condition holds
>        // ... method body
>      }                   // automatic unlock at the end
>    }
>  }
>
> Assuming lock.lock() returns a temporary wrapper object (let's call it a
> "Locker" for this discussion), where Locker implements AutoCloseable, and
> its close() method calls lock.unlock().
> That'll make the API look and feel quite similar to the built-in
> "synchronized () { ... }" syntax. With escape analysis and scalar
> replacement implemented correctly in the VM, this temporary Locker object
> wouldn't incur much (or any) runtime cost after optimized JIT'ing, so it
> feels like a pure win to me.
>
> What do you think?
>
> Best regards,
> Kris (OpenJDK username: kmo)
>