clebertsuconic commented on a change in pull request #2522: ARTEMIS-2239
Zero-copy NIO/MAPPED TimedBuffer
URL: https://github.com/apache/activemq-artemis/pull/2522#discussion_r251006945
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File path:
artemis-journal/src/main/java/org/apache/activemq/artemis/core/io/buffer/TimedBuffer.java
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@@ -358,13 +358,7 @@ public boolean flushBatch() {
bytesFlushed.addAndGet(pos);
}
- final ByteBuffer bufferToFlush =
bufferObserver.newBuffer(bufferSize, pos);
- //bufferObserver::newBuffer doesn't necessary return a buffer
with limit == pos or limit == bufferSize!!
- bufferToFlush.limit(pos);
- //perform memcpy under the hood due to the off heap buffer
- buffer.getBytes(0, bufferToFlush);
-
- bufferObserver.flushBuffer(bufferToFlush, pendingSync,
callbacks);
+ bufferObserver.flushBuffer(buffer.byteBuf(), pendingSync,
callbacks);
Review comment:
I wish it was that simple.
that's only viable if your write operation is synchronous.
That's probably ok with NIO or Mapped, but it's definitely not ok with
libaio.
If you allow the inner buffer to be reused like that, TimedBuffer will be
making changes to a buffer that's been submitted to the kernel, and you may
endup with wrong data.
And that kind of race is hard to catch.
You can only that do this kind of thing on NIO or Mapped, assuming their
buffers will be copied to the file right away.
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