Fix: Race Condition and NullReferenceException in P4Server.LastResult…

[SolarianZ]

Fix: Race Condition and NullReferenceException in P4Server.LastResults Property

Description

The current implementation of the LastResults property suffers from two critical thread-safety issues.

1. NullReferenceException in Getter

If the get accessor is called before the set accessor has initialized the _lastResultsCache field, a NullReferenceException will be thrown. This occurs because the code attempts to call _lastResultsCache.ContainsKey(...) when _lastResultsCache is null.

2. Critical Race Condition in Setter

The set accessor contains a flawed double-checked locking pattern. If two or more threads enter the setter simultaneously when _lastResultsCache is null:

• Both threads will pass the if (_lastResultsCache == null) check.
• Each thread will create its own separate Dictionary instance and assign it to _lastResultsCache.
• Consequently, the threads will lock on different object instances, completely defeating the purpose of the lock.

This race condition leads to lost updates and unpredictable behavior, as the threads are not synchronizing access to a single shared resource.