On 2/21/21 7:28 PM, Preetpal wrote: > I decided to implement what I meant (single application (executable) > instance restriction) using the Windows API (since my application only > runs on Windows currently anyways):
I achieve it with 'flock' (man 2 flock) on Linux. My case is different thoug: It allows me to have single writer and many readers of program data, which is kept inside a cache directory. All instances start with read permissionss to exclude any potential writer. Once a writer grabs the lock for writing, no other writer or reader can exist, etc. A nice side effect that I realized was since there is only one writer, the lock file itself stores progress information so that other instances can say something like "Waiting for the writer to finish: 75%" by reading from the lock file itself. :)
Works like a charm except flock operations are not atomic; so some care is needed. For example, the writer cannot assume there were no other writers when it "drops" its access right to a reader. It has to check some signature to make sure that everything is expected.
Ali
