In my case, Emulator: Process finished with exit code 0 error started after I pressed on Restart in the Emulator.
It happened because in Android Studio 3.0 and up versions, the emulator saves the states of the current screen to launch it very quickly at next time. So when I pressed on Restart it closes emulator by saving state as Restart. So when I launch/start the emulator, it executes the Save States as Restart and then after emulator is not started automatically. So basically it stuck in to Save States of Restart.
I don't want to delete existing emulator and create a new one.
My default Boot Option of Emulator was Quick boot in AVD.
By doing Cold Boot Now from AVD (Android Virtual Device) Manager, it starts emulator again in normal mode without Save State.
Cold boot start emulator as from power up.