Very Computer

by **Alan Murph** » Sat, 31 Mar 2001 20:37:39

Hi,

whats mechanism can be used to take a record lock on a file (using the
fcntl() call), in a posix multi threaded application. Seems to me that
these locks are process based, and therfore multiple threads within the same
process are treated as the same thing.

Any pointer would be appreciated

Thanks Alan

by **Dave Butenho** » Sat, 31 Mar 2001 23:25:18

> whats mechanism can be used to take a record lock on a file (using the
> fcntl() call), in a posix multi threaded application. Seems to me that
> these locks are process based, and therfore multiple threads within the same
> process are treated as the same thing.

> Any pointer would be appreciated

This has been discussed several times before. Yes, fcntl() locks are
process-based, for a number of reasons historical and pragmatic. Some people
have successfully built a two-level file locking strategy that uses mutexes
between threads within a process and fcntl() between processes. Essentially,
you reference count the fcntl() lock(s) so that the process holds an fcntl()
lock whenever any thread within the process has an area locked; if more than
one thread within the process is interested in the same file area, they
synchronized among themselves using a mutex. I believe that sample code may
have been posted. Search the newsgroup archives, if you can find a good server.
(I don't know what the state of Deja is now; it was always a good one, and may
be again if the transfer of control has been straightened out.)

| Compaq Computer Corporation POSIX Thread Architect |
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Very Computer

Using fcntl() record locks with threads

Using fcntl() record locks with threads

Using fcntl() record locks with threads