[GitHub] zhouxinyu opened a new pull request #220: [ROCKETMQ-332] MappedFileQueue#findMappedFileByOffset is not thread safe, which will cause message loss.

[GitBox <gi...@apache.org>]

zhouxinyu opened a new pull request #220: [ROCKETMQ-332] MappedFileQueue#findMappedFileByOffset is not thread safe, which will cause message loss.
URL: https://github.com/apache/rocketmq/pull/220
 
 
   ## What is the purpose of the change
   
   Fix concurrent bug in MappedFileQueue#findMappedFileByOffset, which may cause message loss
   
   ## Brief changelog
   
   
   The `findmappedfilebyoffset` method may return the wrong mapped file or null if the delete behavior occurs concurrently.
   
   So change the find process:
   
   1. Find the target mapped file by calculated index.
   2. Verify the target mapped file is right.
   3. Iterate the whole list and find the right mapped file.
   
   In most cases, it's a O(1) method and will be degrade to O(n) if the concurrent issue occurs.
   
   ## Verifying this change
   
   Review the source code and run the unit/it tests
   
   Follow this checklist to help us incorporate your contribution quickly and easily:
   
   - [x] Make sure there is a [JIRA issue](https://issues.apache.org/jira/projects/ROCKETMQ/issues/) filed for the change (usually before you start working on it). Trivial changes like typos do not require a JIRA issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue. 
   - [x] Format the pull request title like `[ROCKETMQ-XXX] Fix UnknownException when host config not exist`. Each commit in the pull request should have a meaningful subject line and body.
   - [x] Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
   - [x] Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add integration-test in [test module](https://github.com/apache/rocketmq/tree/master/test).
   - [x] Run `mvn -B clean apache-rat:check findbugs:findbugs checkstyle:checkstyle` to make sure basic checks pass. Run `mvn clean install -DskipITs` to make sure unit-test pass. Run `mvn clean test-compile failsafe:integration-test`  to make sure integration-test pass.
   - [x] If this contribution is large, please file an [Apache Individual Contributor License Agreement](http://www.apache.org/licenses/#clas).
   

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