New submission from Oleksiy Markovets:
INTRODUCTION
While embedding python script in c++ application I faced random crashes
with error:
Fatal Python error: Py_EndInterpreter: not the last thread
Aborted
Even though I explicitly join each thread created with *threading*
module. Please see attachment, this is simplest python script +
c++ code which demonstrates problem.
By using threading.setprofiler I was able to make problem appear each run.
If you uncomment time.sleep(1) problem won't reproduce.
Note:
In main.cpp I manually create separate interpreter because in real-life
application is multi-threaded and different thread uses different interpreters
for at least some sand-boxing.
INVESTIGATION
I did some investigation, and here is what I found out:
* Each new thread is started by calling *thread_PyThread_start_new_thread* from
threadmodule.c.
Basically this function creates new thread which executes *t_bootstrap* and
adds this
thread to interpreter's thread list.
* *t_bootstrap* executes python function *Thread.__bootstrap* and when it's
done, removes
thread from interpreter's thread list.
* *Thread.__bootstrap* runs *Thread.run()* (actually python code which should
be executed
in separate thread) and when it's done calls *Thread.__stop* (which by mean of
condition
variable sets Boolean flag Thread.__stopped)
* *Thread.join* doesn't wait thread to exit, it only waits for
*Thread.__stopped* flag
to be set.
So here is race condition:
When main thread finished *Thread.join* it's only guaranteed that *Thread.run*
is finished, but *t_bootstrap* still may be running (interpreter's thread list
is not cleared).
POSSIBLE SOLUTION
To call Thread.__stop from *t_bootstrap* (instead of Thread.__bootstrap) after
removing thread from interpreter's thread list.
Or do not use detached threads and call something like *pthread_join* in
*Thread.join*.
Which is IMHO much clearer approach but also requires much more efforts.
--
components: Extension Modules
files: main.cpp
messages: 246035
nosy: Oleksiy Markovets
priority: normal
severity: normal
status: open
title: Race condition and crash when embedding multi-thread script
type: crash
versions: Python 2.7
Added file: http://bugs.python.org/file39840/main.cpp
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