fsync() is a function similar to
fflush(), however where
fflush() only instructs the application to flush its internal buffers out to the OS,
fsync() further instructs the OS to flush its buffers to physical storage, ensuring a completed and persisted write before returning any success. PHP provides plain stream wrappers for most common file system functions inherited from C and is indeed one of few major languages to not provide any interface to
fsync. This RFC proposes implementing
fsync in core.