The QtLockedFile class extends QFile with advisory locking functions.
Поправь ссылку.
В unix-е можно делать только "лёгкие" локировки. Что QtLockedFile и делает:
The file locks are advisory. This means that nothing prevents
another process from manipulating a locked file using QFile or
file system functions offered by the OS. Serialization is only
guaranteed if all processes that access the file use
QLockedFile. Also, while holding a lock on a file, a process
must not open the same file again (through any API), or locks
can be unexpectedly lost.
Хотя, может
andrew.k этого будет вполне достаточно.