kaisun2000 commented on a change in pull request #1295:
URL: https://github.com/apache/helix/pull/1295#discussion_r483319148
##########
File path:
zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/ZkClient.java
##########
@@ -222,22 +226,16 @@ protected ZkClient(IZkConnection zkConnection, int
connectionTimeout, long opera
_asyncCallRetryThread.start();
LOG.debug("ZkClient created with _uid {}, _asyncCallRetryThread id {}",
_uid, _asyncCallRetryThread.getId());
- connect(connectionTimeout, this);
-
- // initiate monitor
- try {
- if (monitorKey != null && !monitorKey.isEmpty() && monitorType != null
&& !monitorType
- .isEmpty()) {
- _monitor =
- new ZkClientMonitor(monitorType, monitorKey, monitorInstanceName,
monitorRootPathOnly,
- _eventThread);
- _monitor.register();
- } else {
- LOG.info("ZkClient monitor key or type is not provided. Skip
monitoring.");
- }
- } catch (JMException e) {
- LOG.error("Error in creating ZkClientMonitor", e);
+ if (monitorKey != null && !monitorKey.isEmpty() && monitorType != null &&
!monitorType
+ .isEmpty()) {
+ _monitor =
+ new ZkClientMonitor(monitorType, monitorKey, monitorInstanceName,
monitorRootPathOnly,
+ _eventThread);
Review comment:
Maybe I mis-understand what do you mean. Can you draw the code a little
bit more specific?
from the above pseduo code
```
_monitor = new ZkClientMonitor();
// Comment that we need to update the _monitor in the event lock to avoid
missing any records about event thread.
connect(connectTimeout, this, _monitor);
_monitor.register()
```
Assertion: construction of ZkMonitor and ZkThreadMonitor and their
registration must be done before the first doAsyncSync() is sent out, or you
have race condition of missing some read/write.
In the above pseudo code, `_monitor.register()` is too late, the first
sycn() is already out and it may complete earlier than this register(). This
violate the above assertion. You may miss one increase of read counter.
I may not fully understand your idea. Let us be more specific. As long as it
works, I can change it to that way.
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