Ensure access to the `filesLoader` field of `BasicDirectoryModel` is synchronized.
Without synchronization, a thread checks if `filesLoader` is not null and creates a new `FilesLoader` thread. If the thread is pre-empted between these two operations, another thread or even several threads can see the `null` value and create new `FilesLoader` threads. The same way, `BasicDirectoryModel.invalidateFileCache` needs to be synchornized to interrupt the current `filesLoader` and assign `null`. This bug allows reproducing `ConcurrentModificationException` seen in [JDK-8323670](https://bugs.openjdk.org/browse/JDK-8323670) and [JDK-8307091](https://bugs.openjdk.org/browse/JDK-8307091) using the test in PR #18109. ------------- Commit messages: - Remove volatile modifier from DoChangeContents in FilesLoader - Remove synchronized modifier from DoChangeContents.run - Declare addStart and remStart in DoChangeContents as final - Reverse condition in DoChangeContents.run to decrease indentation - Remove cancelRunnables - Declare newFiles as final - Remove redundant fileSystem variable in FilesLoader.run0 - Create FilesLoader inside synchronized section Changes: https://git.openjdk.org/jdk/pull/18111/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18111&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8325179 Stats: 61 lines in 1 file changed: 14 ins; 23 del; 24 mod Patch: https://git.openjdk.org/jdk/pull/18111.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/18111/head:pull/18111 PR: https://git.openjdk.org/jdk/pull/18111
