Proposal: Automatic Resource Management

[Bob Lee]

On Tue, Mar 3, 2009 at 10:13 PM, Neal Gafter <neal at gafter.com> wrote:

> It depends on what libraries are provided, but I'd expect it to be
> something like
>
> try {
>    with (InputStream in : new FileInputStream(src))
>            with (OutputStream out : new FileOutputStream(dest)) {
>         byte[] buf = new byte[8 * 1024];
>        int n;
>        while ((n = in.read(buf)) >= 0)
>            out.write(buf, 0, n);
>    }
> } catch (IOException ex) {
>    showDialog("Copy failed.");
> }
>
> Looks about as nice, except for the advantage that the semantics don't
> have to be hardcoded into the language.


FWIW, the lack of {} after the first with() cause me to take a double take.
The BGGA version is verbose and user-unfriendly enough that I'd still want
Automatic Resource Management. Closing I/O resources properly is one of the
biggest challenges for Java programmers; it deserves a first class solution.

Can you please show me how to
> handle the following BGGA example using this proposal:
>
> lockWrite(lock) {
>    clientCount++;
> }
> lockRead(lock) {
>    return field.getValue();
> }


You can't, nor does the proposal attempt to address this use case. I'm not
personally interested in addressing that use case at this time because it's
easy enough to write:

   writeLock.lock();
   clientCount++;
   writeLock.unlock();
   readLock.lock();
   try {
     return field.getValue();
   } finally {
     readLock.unlock();
   }

and save yourself two allocations and an implicit layer of indirection.

Bob