Re^2: detecting directory in perl

[MidLifeXis]

A common idiom would also be to open a tempfile with a sufficiently randomized name (see File::Temp, do your writing there, and then after obtaining a lock on the output file, rename or move the tempfile into place over the output file. (emphasis added)

Race condition waiting to happen (at least as I am reading your statement). Have the lock signal the ability to modify the file (lock first, write second). If you don't lock first, you risk clobbering someone else's changes:

• You create a tmp file
• They create a tmp file
• They lock
• They overwrite
• They unlock
• You lock
• You overwrite
• You unlock

The changes made by "They" are now gone. Lock before read just to ensure that you have the newest data. Otherwise, I agree.

[davido]

You lock the target before creating a temp, and as a final step move the temp in place over the target. If you fail to get a lock on the target to begin with, stop there.

After re-reading my post I see that my words didn't reflect the process I had in my head when I wrote them. I've updated. Thanks for noticing and bringing it to my attention! :)