zhouxinyu commented on pull request #3848:
URL: https://github.com/apache/rocketmq/pull/3848#issuecomment-1040031406
> @zhouxinyu It may have difficulty doing the lazy mapping safely while the
mapped file is being used concurrently, which may need to introduce a lock.
>
> The current code is clear, avoiding the anxiety of concurrent error, and
is used for a long time in the production env.
>
> BTW, if you have a simple way to implement the lazy mapping, it is ok to
show it in detail.
Yeap, a lock is necessary for this lazy mapping solution, implementing it is
not too complex, we convert direct access `this.mappedByteBuffer` to a getter
method `this.getBuffer`:
```
public MappedByteBuffer getBuffer() {
if (this.mappedByteBuffer != null) {
return this.mappedByteBuffer;
}
synchronized (this) {
if (this.mappedByteBuffer == null) {
this.mappedByteBuffer = this.fileChannel.map();
}
}
return this.mappedByteBuffer;
}
```
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