Semaphore files have their uses:
- What if the file you want to lock doesn't exist yet?
- What if you want to lock all the files in a directory?
- What if you want to lock another resource that isn't even a file, or doesn't lend itself to being flock()ed?
Also, if you are going to just lock the file you want to modify instead of using a semaphore file, why are you opening the file, flock()ing the filehandle, then opening the file again?
Open the file with the permissions you'll need to perform the operations you've got planned, flock() it, do the operation, close the file.
Advisory locking never "plays well with others" if one of the those "others" ignores a lock, be it on a semaphore file, or the file itself.
Generally, advisory locks are good enough.
I'd be surprised if there isn't a way of controlling other processes, and making sure that they go through filehandling/locking properly.
BazB
Update: Correction. Removed discussion on bad example (since author _knows_ it's bad :-)
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