You can lock a file for such purposes as maintaining a hit counter on a website, by using OmniMark's omvfs library.
To lock a file for such a hit counter, create a program like this one:
import "omvfs.xmd" prefixed by vfs. process local vfs.file counter-file local stream hit-count ; set up a vfs.file for the counter set counter-file to vfs.open "counter.txt" for vfs.read-write-mode vfs.lock counter-file ; read and increment the hit-count set hit-count to "d" % vfs.read counter-file + 1 ; output the hit-count output hit-count ; output the updated counter vfs.move-cursor counter-file to 0 set vfs.write counter-file to hit-count vfs.unlock counter-file ; a catch block for handling errors in this program catch #external-exception identity catch-id message catch-msg put #ERROR 'An error occurred while accessing a VFS file' put #ERROR '%g(catch-id) : %g(catch-msg)%n'
This program does the following:
hit-count, and the VFS file
counter-fileto the file named "counter.txt" by using open.
counter-filefor the duration of this program.
hit-countby adding 1 to the contents of
counter-fileto the value of
hit-countusing write, thus updating the file "c:\counter.txt".
counter-filewith the omvfs library function unlock so another process can update it.