I can't find a way to have a script create a file in a directory to be served by Apache without exposing itself to race conditions. I can't use tempnam because that doesn't give me control over the file extension. I can't use file_exits because that will race. I can't use fopen because I can't use O_EXCL|O_CREAT.

I can work around this by creating subdirectories, because mkdir fails if the directory already exists. But putting one file per directory is hardly ideal.

Having a way to use O_EXCL|O_CREAT --- that is, open a file for writing, creating it, and failing if it already exists all atomicly --- would be a big help.