Locking and concurrent edits

Not sure if / how this should be handled.

 

The basic problem is if two or more people are performing edits concurrently. What should happen at save time, ie two edit sessions start at the same time. Session 1 changes a few lines and saves. Session 2 is not aware of any changes made by session 1 and when saved will completely remove them...

 

I have thought through the following process (up to a point), but need some help on how to handle...

 

Edit

• Does a lock file exist
  • No -> perform action 1
  • Yes -> Is lock file less than ''nn'' seconds old (average time on edits)
    • No -> perform action 1
    • Yes -> Someone else is already editing. Issue a message to this effect and offer chance to continue edit or wait (y/n)
      • No -> simply show page again
      • Yes -> perform action 1

 

action 1

• create lock file, ie <pagename>.<timestamp>.lock
• begin the edit session

 

Save

• Has file been saved since my session began ? (possibly pass ,timestamp> via php_sessions)
• No -> Save file, and remove lock file for my <timestamp>
• Yes -> Someone else has saved since I began editing.....

 

OK this is where I am stuck. What actions should be taken now ?

• perform a compare and try and accomodate previous changes ? if so, HOW!!!!
  • What if: create a diff of first save from original version, create a diff of second save from original version. If no lines conflict between the two, apply both diffs to original and save. If conflict (like both change same line) then present diffs to second author for manual merging.
• simply overwrite what someone else has done ?
• decline the save and force new edit session using new file ?
• Present the author of the last change a diff like view of the page in preview mode and have him to fix it. http://www.holomind.de/phpnet/diff.php and http://www.holomind.de/phpnet/diff.src.php might help.