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KAFKA-10899: Producer's BufferPool closing check #9817

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unlizhao wants to merge 1 commit into from
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KAFKA-10899: Producer's BufferPool closing check #9817

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7 changes: 6 additions & 1 deletion clients/src/main/java/org/apache/kafka/clients/producer/internals/BufferPool.java
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Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,7 @@ public class BufferPool {
private final Metrics metrics;
private final Time time;
private final Sensor waitTime;
private boolean closed;
private volatile boolean closed;

/**
* Create a new buffer pool
Expand Down Expand Up @@ -212,10 +212,15 @@ protected void recordWaitTime(long timeNs) {
/**
* Allocate a buffer. If buffer allocation fails (e.g. because of OOM) then return the size count back to
* available memory and signal the next waiter if it exists.
*
* if producer is closing, will throw close-exception
*/
private ByteBuffer safeAllocateByteBuffer(int size) {
boolean error = true;
try {
if (this.closed) {
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@chia7712 chia7712 Jan 6, 2021

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It is not holding the lock so this pool can be closed anytime. How we know the "best" place to check the close flag?

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@unlizhao unlizhao Jan 7, 2021

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@chia7712 thanks for your reviewed. This is what I thought when I wrote this code

In the PR of #3053, for efficiency, the operation of allocating memory is moved out of the locked code block.
Subsequent modifications should be based on this consensus, and do some time-consuming operations without locking.

So what we can do is to try our best to check whether the memory can be allocated before allocating, and reduce the operation of allocating memory, just like the 'fail-fast' mechanism.

In this scenario, both BufferPool#allocate() and BufferPool#close() compete for locks.
Here we can think that lock blocking is more likely to occur in concurrent cases.

Finally, even if the memory is allocated in the close state, there is a plan to release the memory. Therefore, this COMMIT is like an optimization rather than bug-fix

throw new KafkaException("Producer closed while allocating memory");
}
ByteBuffer buffer = allocateByteBuffer(size);
error = false;
return buffer;
Expand Down