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Erlang / Erlang Advanced Interview questions

Explain the internal working of code:purge/1 and code:soft_purge/1?

Both functions remove the old (previous) version of a module from memory, freeing it up so a future reload has room, but they differ in how they treat processes still executing that old code.

code:purge/1code:soft_purge/1
Unconditionally kills any process still running the old version. Checks first; if any process is still running the old version, it does nothing and returns false.
Guarantees the old version is gone afterward. Only purges if it's already safe — returns true only when nothing was running it.

Release upgrade tooling typically calls soft_purge first, in a retry loop, giving in-flight processes time to naturally cycle back through their own module (and switch to the new version) before resorting to a hard purge that would forcibly terminate anything still lagging behind.

What does code:soft_purge/1 do if a process is still running the old module version?
Why do release upgrade tools usually prefer soft_purge in a retry loop before falling back to purge?

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