A gotcha with fcntl file locking


Today I ran into an issue with fcntl(2) file locking[1] on Linux. A little research confirmed my fear:

From On the Brokenness of File Locking:

The worst part however is that POSIX locks are automatically released if a process calls close() on any (!) of its open file descriptors for that file.

The whole post is well worth a read.

  1. Which is what OpenJDK uses for FileChannel#lock.