Issue1026

I've mentioned before that I thought our list object wasn't thread safe 
at all, but it somewhat is -- many PySequenceList methods are 
synchronized.

Some list operations apparently aren't going through PySequenceList and 
aren't thread safe. One I can reproduce somewhat occurs when I throw a 
bunch of connections/threads at a Pylons hello world app (ab -n 1000 -c 
20)

18:02:35,413 INFO  [paste.httpserver.ThreadPool] Cannot use 
kill_thread_limit as ctypes/killthread is not available
serving on 0.0.0.0:5000 view at http://127.0.0.1:5000
java.lang.IndexOutOfBoundsException: Index must be between 0 and 1, but 
was 5
        at org.python.core.AbstractArray.remove(AbstractArray.java:360)
        at org.python.core.PyObjectList.remove(PyObjectList.java:127)
        at 
org.python.core.PySequenceList.remove(PySequenceList.java:107)
        at org.python.core.PyList.del(PyList.java:100)
        at org.python.core.PyList.list_remove(PyList.java:579)
        at org.python.core.PyList$list_remove_exposer.__call__(Unknown 
Source)
        at org.python.core.PyObject.invoke(PyObject.java:2744)
        at 
paste.httpserver$py.worker_thread_callback$51(/Users/pjenvey/src/python/
pylons-related/Paste/paste/httpserver.py:859)
        at 
paste.httpserver$py.call_function(/Users/pjenvey/src/python/pylons-
related/Paste/paste/httpserver.py)
        at org.python.core.PyTableCode.call(PyTableCode.java:178)
        at org.python.core.PyTableCode.call(PyTableCode.java:399)
        at org.python.core.PyTableCode.call(PyTableCode.java:294)
        at org.python.core.PyFunction.__call__(PyFunction.java:212)
        at org.python.core.PyMethod.__call__(PyMethod.java:101)
        at org.python.core.PyObject._callextra(PyObject.java:395)
        at threading$py.run$40(/Users/pjenvey/src/java/jython-
trunk/dist/Lib/threading.py:200)
        at threading$py.call_function(/Users/pjenvey/src/java/jython-
trunk/dist/Lib/threading.py)
        at org.python.core.PyTableCode.call(PyTableCode.java:178)
        at org.python.core.PyTableCode.call(PyTableCode.java:399)
        at org.python.core.PyTableCode.call(PyTableCode.java:294)
        at org.python.core.PyFunction.__call__(PyFunction.java:212)
        at org.python.core.PyMethod.__call__(PyMethod.java:101)
        at org.python.core.PyObject.__call__(PyObject.java:254)
        at org.python.core.PyObject.invoke(PyObject.java:2731)
        at 
threading$py._Thread__bootstrap$41(/Users/pjenvey/src/java/jython-
trunk/dist/Lib/threading.py:209)
        at threading$py.call_function(/Users/pjenvey/src/java/jython-
trunk/dist/Lib/threading.py)
        at org.python.core.PyTableCode.call(PyTableCode.java:178)
        at org.python.core.PyTableCode.call(PyTableCode.java:399)
        at org.python.core.PyTableCode.call(PyTableCode.java:294)
        at org.python.core.PyFunction.__call__(PyFunction.java:212)
        at org.python.core.PyMethod.__call__(PyMethod.java:101)
        at org.python.core.PyObject.__call__(PyObject.java:244)
        at org.python.core.FunctionThread.run(FunctionThread.java:19)
Exception in thread worker 11:Traceback (most recent call last):
  File "/Users/pjenvey/src/java/jython-trunk/dist/Lib/threading.py", 
line 209, in _Thread__bootstrap
    self.run()
  File "/Users/pjenvey/src/java/jython-trunk/dist/Lib/threading.py", 
line 200, in run
    self._target(*self._args, **self._kwargs)
  File "/Users/pjenvey/src/python/pylons-
related/Paste/paste/httpserver.py", line 859, in worker_thread_callback
    self.idle_workers.remove(thread_id)
java.lang.IndexOutOfBoundsException: 
java.lang.IndexOutOfBoundsException: Index must be between 0 and 1, but 
was 5

I meant I can reproduce it somewhat easily

New backing implementation of list (and tuple) in trunk as of r6245.
This *may* fix the issue, I'm not certain what thread safety this
particular use case requires (since it's of course not well defined in
Python).

Regardless, the call path is now significantly simplified.

This didn't fix it. We need to make remove thread safe, as well as any 
other basic operations people expect to be thread safe from CPython. The 
ol' effbot FAQ entry is the closest thing to a specification that we 
have here

http://effbot.org/pyfaq/what-kinds-of-global-value-mutation-are-thread-
safe.htm

We can readily just make all the publicly visible methods in PyList 
synchronized, that should accomplish what is discussed in the effbot 
FAQ, without the limitations discussed about using the GIL to effect 
this sort of behavior.

One option that we may wish to exploit is to use other backing 
implementations for PyList.list, namely CopyOnWriteArrayList.

CopyOnWriteArrayList would be a future option of course...

Sure on the synchronization. gListAllocatedStatus looked like it should 
be volatile, too

I highly doubt CopyOnWriteArrayList would be appropriate as list 
mutations are pretty frequent. Trying it wouldn't hurt I guess

Also if we're abandoning MergeState we should probably just nuke that 
file.

CopyOnWriteArrayList would only be an option as a backing store, for the 
usual scenario where readers are the predominant activity. I don't think 
this really needs to be considered until we have optimized for JDK 7 for 
example.

I'll nuke MergeState, with JDK 7 we get back timsort anyway.

Relevant methods are now synchronized as of r6279.

Marking as pending until we have a robust test of expected atomicity of
list ops.

Relevant methods are now synchronized as of r6279.

Marking as pending until we have a robust test of expected atomicity of
list ops.

Nuked MergeState in r6281.

Closing out, based on pjenvey reporting that it's working for him. We 
should have some good robust tests for this, but they're particularly 
tough for thread safety.