Creating instances of Component class is unsafe in multi-thread

[Jun Omae]

The fetch/store operations are not atomic for ComponentManager.components in trac/core.py:115-121,161​. The operations are unsafe in multi-thread.

Trac 0.12rc1 and 0.11.7 have the problem.

Test code

#! /usr/bin/python

import sys
import time
from threading import Thread, Event

from trac import __version__ as VERSION
from trac.core import Component, ComponentManager


class MTComponent(Component):
    def __init__(self):
        pass

class TestThread(Thread):
    def __init__(self, manager, event):
        Thread.__init__(self)
        self.manager = manager
        self.event = event

    def run(self):
        manager = self.manager
        self.event.wait()
        obj = MTComponent(manager)
        self.id = id(obj)

def main():
    print 'Python %s' % sys.version
    print 'Trac %s' % VERSION

    for i in range(0, 100):
        manager = ComponentManager()
        event = Event()
        event.clear()
        threads = []
        for j in range(0, 64):
            thr = TestThread(manager, event)
            threads.append(thr)
            thr.start()
        sys.setcheckinterval(1)
        event.set()
        for thr in threads:
            thr.join()
        ids = set(thr.id for thr in threads)
        if len(ids) != 1:
            print '#%d: Unsafe in multi-thread - %r' % (i, ids)

main()

Result

Python 2.4.3 (#1, Sep  3 2009, 15:37:12)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-46)]
Trac 0.12rc1
#12: Unsafe in multi-thread - set([-1211591892, -1211592340])
#13: Unsafe in multi-thread - set([-1211591796, -1211592116])
#14: Unsafe in multi-thread - set([-1211592180, -1211591700, -1211591732])
#20: Unsafe in multi-thread - set([-1211591348, -1211591732])
#42: Unsafe in multi-thread - set([-1211591188, -1211592308, -1211591156])
#46: Unsafe in multi-thread - set([-1211590932, -1211592052])
#52: Unsafe in multi-thread - set([-1211590548, -1211590516])
#57: Unsafe in multi-thread - set([-1211590196, -1211590964])
#60: Unsafe in multi-thread - set([-1211590004, -1211592116])
#70: Unsafe in multi-thread - set([-1211589300, -1211589684, -1211589332])
#73: Unsafe in multi-thread - set([-1211589140, -1211590868])
#76: Unsafe in multi-thread - set([-1211588948, -1211591220])
#83: Unsafe in multi-thread - set([-1211555700, -1211591860])
#84: Unsafe in multi-thread - set([-1211555764, -1211555636])
#86: Unsafe in multi-thread - set([-1211555508, -1211555700])
#96: Unsafe in multi-thread - set([-1211590548, -1211588820])