On Tue, Jul 12, 2016 at 11:54:18AM -0700, Charles Hixson via Digitalmars-d-learn wrote: > I want to open a file with an exclusive lock. It would be important > that no other thread be able to access the file in write mode, and > desirable that no other thread be able to access the file in read > mode. (Ditto for other processes.) > > stdio.file.lock (or is it stdio.file.File.lock?) seems to demand a > range of chunks to lock, but the file is not fixed in length. Is it > appropriate to just specify the maximum possible number of bytes (i.e. > ulong.max)?
Whether this is even possible depends on your OS. I don't know of any cross-platform way of file-locking that is guaranteed to work everywhere. In Posix there's fcntl(F_RDLCK / F_WRLCK), which I believe is the underlying OS call for File.lock. However, this is only an *advisory* lock, i.e., any other processes accessing the file must also call flock(), otherwise none of its protections apply. It only works between cooperating processes. Linux does have a mandatory locking feature, but it requires the kernel to be specially configured for it, and the filesystem must also support it (and must be mounted with the correct options). Unfortunately it's Linux-specific and probably won't work for any other OS. Windows may have some file-locking mechanism that does what you want, but I'm not familiar with the intricacies of how it works. T -- Why waste time reinventing the wheel, when you could be reinventing the engine? -- Damian Conway
