"William A. Rowe, Jr." <[EMAIL PROTECTED]> writes: > At 07:08 AM 10/20/2002, Bill Stoddard wrote: > >Why do we need to call SetFilePointer to each call of apr_file_write()? In > >the common case where only threads in a single process write to a file, > >calling SetFilePointer is a waste of cycles. If threads from multiple > >processes are writing to a file, then we are broken unless the application > >explicitly serializes access to apr_file_write() > > I'll take a wild guess... > > Unix append mode -always- writes to the end of the file, even when it is > in use by multiple processes. Win32 has no absolute, atomic append > mode for it's file open. > > But you are correct, there is a race here that even the 'emulation' falls > down.
Maybe APR_APPEND needs to be cheap/simple append a la stdio append: we seek to the end of the file at open time and forget about it after that. Then we need new APR_WRITE_AT_END or something better named which is the expensive atomic append. For Unix, this enables O_APPEND on the file and the kernel handles the details. For Win32, this enables acquire-global-mutex + setfileptr + release-global-mutex prior to every write. But then that has issues with non-related processes sharing the mutex. -- Jeff Trawick | [EMAIL PROTECTED] Born in Roswell... married an alien...
