David, It looks like LockRecord does what you'd want to get this port done. If a single-threaded port is all you want you can probably use the logic in the os_win.c file.
The difference in the Win32 and Posix models are the following: Win32: locks are held by file handles Posix: locks are held by processes Win32: different threads can have their own locks if they have private file handles Posix: all threads have to coordinate their locks, and delay closing file handles until no more locks are held I try to avoid Posix locks whenever I can. Good luck, Gé David Pitcher wrote: > Thanks for responding Gé > > There are the usual options of buffered and unbuffered file i/o in > AmigaOS. A given file can be opened either in a shared mode, or an > exclusive mode by a process, but it can also be locked first and then > opened. It cannot be locked individually for a given pthread running in > that process. > > __For coarse grain locking there is Lock( filename, mode )__ > > Lock( ) allows you to lock a given file by name, and you get a lock > descriptor. That lock descriptor can either be SHARED_LOCK ( ACCESS_READ > ) or EXCLUSIVE_LOCK ( ACCESS_WRITE ), indicating more of the intention > of the descriptor rather than causing any limitation on the outcome of a > Read or Write operation on any resulting file descriptor. In any case > the lock descriptor has to be held while its in use. > > You can then access the file descriptor from that lock descriptor safe > in the knowledge that it is yours. > > The problem being that it locks the whole file, rather than individual > records/ranges inside it. This is how I currently implement it to > prevent two different processes both running on the same database from > overwriting each other. > > It works to a fashion, but its not sophisticated like I think it should > be - and reading your reply, it could be. > > __For fine grain lock there is LockRecord( ... ) and LockRecords( ... )__ > > LockRecord( ... ) allows you to lock a given range to yourself ( which I > didn't actually realise I had as an option to be honest until I went > back to the developer documentation for the OS just now ) in either > EXCLUSIVE or SHARED mode. > > LockRecords( ... ) allows you to lock multiple ranges to yourself at > once ( kind of like a lockset ). > > Both of those have optional timeouts, and IMMED suboptions to either > wait for a lock or return straight away if its already locked. > > Now Im not totally sure whether or not the lock record option treats > individual threads as different potential lock holders, thats something > Ill try in a minute ( and it isn't clear from the documentation either > ). But it certainly locks it system wide. > > So following your reply, it indicates that I should follow the Win32 > implementation pattern? Then if I can confirm if threads are treated as > individual lockholders or not I can use the AmigaOS pthread.library to > multi-thread it. If not, it stays single threaded but at least > potentially atomic system wide - which should be enough to make it a > decent enough port. > > Dave.
