Pil0tXia opened a new pull request, #4344:
URL: https://github.com/apache/eventmesh/pull/4344
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Fixes #4341.
### Feature Description
When creating a new WebHookConfig, the `writeToFile` method is invoked to
create a file and write data. The `fileWatchRegister` can monitor file
creation, modification, and deletion. It calls the `cacheInit` method during
creation and modification events to store the WebHookConfig in
`cacheWebHookConfig`.
### Bug Phenomenon
Under normal circumstances, when copying the `webhook.github.eventmesh.all`
configuration file, both ENTRY_CREATE and ENTRY_MODIFY events are generated as
expected:
The bug occurs when calling the `insertWebHookConfig` endpoint for the first
time to create a WebHookConfig. Only the ENTRY_CREATE event is captured
(abnormal; expected behavior is to have both events):
At this point, the file is empty, and the `cacheInit` method writes null to
`cacheWebHookConfig`:
However, the loop ends after one iteration, and `fileWatchRegister` does not
call the `cacheInit` method again after the file has been written with
WebHookConfig data. Consequently, `cacheWebHookConfig` does not have a valid
value, and using the `queryWebHookConfigById` endpoint will not retrieve the
WebHookConfig.
### Initial Solution
I resolved this bug by adding a slight delay after capturing the file event:
```java
try {
assert service != null;
key = service.take();
Thread.sleep(1000);
} catch (InterruptedException e) {
log.error("Interrupted", e);
}
```
With this delay, both ENTRY_CREATE and ENTRY_MODIFY events are captured. The
`for (final WatchEvent<?> event : key.pollEvents())` loop iterates twice,
allowing complete file data reading and the correct creation of WebHookConfig.
This behavior is correct and matches expectations.
### Bug Cause
The bug arises when the JVM retrieves file system events faster than file
write speed. In such cases, the obtained file events and data are incomplete.
When the JVM retrieves file system events slower than file write speed, the
events and data are complete.
In other words, when `fileWatchRegister` captures a file creation event,
without adding a delay, `key.pollEvents()` will return only an ENTRY_CREATE
event, not waiting long enough for the file's content to be fully written to
disk.
File write speed is beyond control, and a fixed delay isn't a robust
solution. Interestingly, I found that this bug doesn't fully reproduce on a
different machine.
### Better Solution
My code should be more robust. A better solution is to ensure the file is
fully created and written before executing actions. Therefore, I listen to the
"ENTRY_MODIFY" event of the file rather than performing `cacheInit(file)` in
the "ENTRY_CREATE" event. This approach provides more certainty in waiting for
complete file writes.
### Documentation
- Does this pull request introduce a new feature? (yes / no)
- If yes, how is the feature documented? (not applicable / docs / JavaDocs /
not documented)
- If a feature is not applicable for documentation, explain why?
- If a feature is not documented yet in this PR, please create a followup
issue for adding the documentation
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