Restricting D applications to a single instance
Ali Çehreli
acehreli at yahoo.com
Mon Feb 22 08:00:06 UTC 2021
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
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