fsync is a straightforward wrapper around the same C function
(implemented on Windows API as _commit() with identical signature).
From the man pages:
fsync() transfers ("flushes") all modified in-core data of (i.e.,
modified buffer cache pages for) the file referred to by the file
descriptor fd to the disk device (or other permanent storage
device) so that all changed information can be retrieved even if
the system crashes or is rebooted. This includes writing through
or flushing a disk cache if present. The call blocks until the
device reports that the transfer has completed.
RFC: https://wiki.php.net/rfc/fsync_function
Closes GH-6650.
cbcfd86026