QFileSystemWatcher::addPath() is slow on my arm macbook. It causes a freeze in Qt Creator (QTCREATORBUG-33191) and I managed to construct a reproducer without Qt Creator, see attached zip.

The reproducer creates 1000 files in a temporary directory, watches the directory, then modifies the files in the temporary directory, and gets a directoryChanged signal (up to here everything good).
After receiving the directoryChanged signal, it will do QFileSystemWatcher::addPath().
Expected behavior: addPath() returns in a timely fashioin
Observed behavior: addPath() spends more than 6 seconds in FSEventStreamFlushSync()

I get following output from the reproducer:

[     0.000] Creating files
[     0.099] Done!
[     0.099] Creating watch!
[     0.133] Done!
[     0.133] Running event loop!
[     0.184] Modifying folder!
[     0.244] Done!
[     0.251] Directory Changed!
[     0.251] Adding path in onDirectoryChanged
[     6.918] Done!

Note the 6 seconds difference between "Adding path in onDirectoryChanged" and "Done!".

Also note that in QTCREATORBUG-33191, the CMake extension actually watches a folder with ~9000 files when opening the qt project and building qtdeclarative, and there we wait for more than 6 seconds.