Issue 36487: Make C-API docs clear about what the "main" interpreter is (original) (raw)

I should have added something like this earlier, but here are key points to consider covering:

• "main" interpreter is the original, created when the runtime initializes
• historically almost always the only Python interpreter in a process
  • this is changing (more projects using subinterpreters, PEP 554)
  • in the "python" executable, subinterpreters available via extension modules (but uncommon)
• it has extra responsiblities:
  • signal handling, in main thread
  • "pending calls", in main thread
    • not necessarily something to publicize :)
  • running in the "main" thread
    • can be taken over by a sub-interpreter, but not likely
  • execution during runtime initialization
  • usually (always?) the active interpreter during runtime finalization
  • others?
• no strong link between interpreters (e.g. main <--> sub <--> sub)
  • no record of what interpreter was active (if any) when a subinterpreter was created
  • no "parent" interpreter
  • thread states may share thread ID
• a bunch of stuff in the C-API and in the runtime still assumes that the main interpreter is running in the current OS thread
• other stuff?

Not all of that necessarily belongs there in the docs, but a lot of it does. :)