Liya Fan created ARROW-6723:
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Summary: [Java] Reduce the range of synchronized block when
releasing an ArrowBuf
Key: ARROW-6723
URL: https://issues.apache.org/jira/browse/ARROW-6723
Project: Apache Arrow
Issue Type: Improvement
Components: Java
Reporter: Liya Fan
Assignee: Liya Fan
When releasing an ArrowBuf, we will run the following piece of code:
private int decrement(int decrement) {
allocator.assertOpen();
final int outcome;
synchronized (allocationManager) {
outcome = bufRefCnt.addAndGet(-decrement);
if (outcome == 0) {
lDestructionTime = System.nanoTime();
allocationManager.release(this);
}
}
return outcome;
}
It can be seen that we need to acquire the lock for allocation manager lock, no
matter if we need to release the buffer. In addition, the operation of
decrementing refcount is only carried out after the lock is acquired. This
leads to unnecessary resource contention, and may degrade performance.
We propose to change the code like this:
private int decrement(int decrement) {
allocator.assertOpen();
final int outcome;
outcome = bufRefCnt.addAndGet(-decrement);
if (outcome == 0) {
lDestructionTime = System.nanoTime();
synchronized (allocationManager) {
allocationManager.release(this);
}
}
return outcome;
}
Note that this change can be dangerous, as it lies in the core of our code
base, so we should be careful with it. On the other hand, it may have
non-trivial performance implication. As far as I know, when a distributed task
is getting closed, a large number of ArrowBuf will be closed simultaneously. If
we reduce the range of the synchronization block, we can significantly improve
the performance.
What do you think?
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