Check if the Main Thread is still alive from another thread

Question

How can I check if the Main Thread is alive from another ( non-daemon, child ) thread?

The child thread is a non-daemon thread and I'd like to check if the Main thread is still running or not, and stop this non-daemon thread based on the result.

( Making the thread daemon is not good for my situation because my thread writes to stdout which creates problems when the thread is set as a daemon)

Using python 2.7

Answer 1

• For Python 2.7 you can try this:

  for i in threading.enumerate():
     if i.name == "MainThread":
         print i.is_alive()
  

  The usage of lower camel case in function names is deprecated and so you should be using i.is_alive() instead of i.isAlive().

• If you like one-liners try this:

  is_main_thread_active = lambda : any((i.name == "MainThread") and i.is_alive() for i in threading.enumerate())
  

  Then call is_main_thread_active() to check if the Main Thread is active.

  For one time use, however, you could use this directly without creating a function.

  any((i.name == "MainThread") and i.is_alive() for i in threading.enumerate())

• Check this page for more info about threading.

• In python 3.4 a dedicated function to return the main thread exists and so you can use this one liner to see if your main thread is still alive..

  threading.main_thread().is_alive()
  

Hope this helps you.

Answer 2

apart from what Raghav's said, you can also save the main thread in a global variable from inside it like:

mainThread = threading.currentThread() # current_thread() in py 3

then use mainThread.isAlive().