operating system - Single instance of application

Question

In general, what are the ways that we can make sure a single instance of application? This is not specific to any programming language. I just want to know how we can prevent starting the second instance of an application?

question from:https://stackoverflow.com/questions/65914077/single-instance-of-application

Answer 1

I can think of two ways:

1. Application side: Create a lockfile somewhere on a specified location. If it already exists, another instance is running, otherwise create the lockfile. If the program exits, delete the lockfile. (For example X or firefox do this)

2. OS side: (Although this wouldn't be that practical)

2.1. For all started binaries, store some hash value somewhere. If an binary is already started, (E.g. the hash value is already available), don't start it.

2.2. This will fail quite often, as you could run only ONE JVM, ONE Python interpreter and so on. So to improve this, the OS could add the commandline arguments for example to the hash value.