If syncing on directory is not important, then sizeInBytes can be an AtomicLong?
On Fri, Nov 27, 2009 at 8:37 AM, Michael McCandless
<luc...@mikemccandless.com> wrote:
> RAMFile has this method:
>
> final synchronized byte[] addBuffer(int size) {
> byte[] buffer = newBuffer(size);
> if (directory!=null)
> synchronized (directory) { // Ensure addition of
> buffer and adjustment to directory size are atomic wrt directory
> buffers.add(buffer);
> directory.sizeInBytes += size;
> sizeInBytes += size;
> }
> else
> buffers.add(buffer);
> return buffer;
> }
>
> But in working on LUCENE-2095, I'm seeing a deadlock, because that
> method first syncs on RAMFile and then tries to sync on directory,
> while the MockRAMDirectory.crash method, and I think maybe other
> places, do the reverse. I remember also hitting a different deadlock
> from this in the past, and working around it.
>
> I'd like to break the deadlock by changing RAMFile to this:
>
> final byte[] addBuffer(int size) {
> byte[] buffer = newBuffer(size);
> synchronized(this) {
> buffers.add(buffer);
> sizeInBytes += size;
> }
>
> if (directory != null) {
> synchronized (directory) {
> directory.sizeInBytes += size;
> }
> }
> return buffer;
> }
>
> But, then, the addition of the buffer and the change of sizeInBytes is
> no longer atomic wrt the directory (as the comment says).
>
> So my question is... is this change OK? Why is/was it so crucial that
> the sizeInBytes & RAMFile's buffers really change only atomically?
> Ie, it seems harmless if RAMDirectory.sizeInBytes() might not include
> a buffer that's in the process of being added...?
>
> (I do see TestRAMDirectory.testRAMDirectorySize requires this
> atomicity, but, I can fix the test to only check the size in the
> end...).
>
> Mike
>
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