Wednesday, April 24, 2013

Race Conditions Resulting in Double Free

In working with Qt and its slot and signals, I've encountered quite a few double free errors despite my use of QSharedPointer. One particularly puzzling situation, I have stumbled upon involves the following model:

  1. An object, say controller, owns another object, say agent
  2. Controller subscribes to a event (signal) from agent called closing
  3. If the agent issues a closing signal, the controller removes it from a list of known agents (effectively freeing it as a result of the QSharedPointer).
  4. If the controller is closing, it calls close on the agents and then removes them from its list.
The double free occurs when the controller closes before the agents, effectively causing the agent to notify the controller it is being closed while both are being destructed. This probably occurs because the Qt signal disconnect code would happen in the base destructor (QObject), which would be called after the Session destructor. The easy resolution was to disconnect all signals except destroyed.
Posted by David Wolinsky at 9:18 PM

3 comments:

  1. MarianJuly 3, 2024 at 4:32 AM

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  2. MarianJuly 3, 2024 at 4:38 AM

    Race situations can have a significant effect on software security and reliability, such as those that result in a double free. These problems frequently result from concurrent processes that are not properly synchronized. Investigate scholarly insights for a deeper grasp; occasionally, you may need to buy dissertation discussion resources that go into complex solutions for such important programming problems.

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  3. Mary WalkerJuly 6, 2024 at 5:21 AM

    It appears that the race condition that is causing the double free issue you are experiencing is quite complex. To ensure proper handling, it may be beneficial to explore advanced synchronization techniques or even redesign certain parts of your system. If anyone has encountered a similar problem or has insights, I would greatly appreciate your advice. By the way, if anyone can provide help with dissertation, that would be fantastic.

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