A WPF UI has a user control that use COMs and DirectShow.NET. The WPF UI display the time used to transform a video frame.
I declare a float in the WPF UI. The float is passed by reference to my COM filter. The COM filter increments the float, each time a frame is transformed.
A timer is used to display the float to the screen every x mili seconds.
Also, keep in mind that multiple frames are modified per second, which means that the float is written multiple time per second. This is why I decided to not go with events and go with a reference float instead.
The same float is being read and written by two different threads, which cause a crash. The faster the read timer, the faster the crash occurs... for obvious reasons.
Do I need to somehow lock the float in both threads ? If so, how ?
If possible, I want to keep the float a simple variable, not make it a property and not make it a class member. ( else it would require multiple changes in my COM, but I will do it if it's the only way. )
PS: I've read MultiThreading COMObject and UI Thread (C#) but couldn't understand it and not sure if it applies to my case.
Luaan said in the comments,
Also, don't forget that .NET is allowed to move the objects in memory. The address you passed doesn't necessarily still point to the float. In fact, for newly created objects, it's almost guaranteed that they will move on the next heap compaction.
This made me realise that it is wrong to pass variables by reference from C# to a C++ COM, for a long process.
Instead of sending my variables by reference for a long process ( about a minute ), I call the method every second with the variables passed by reference to get samples of the values.
Also, the COM writes all the values to a file. So I can compute the exact sum at the end.
Doing so removed the COM errors of writing to a float that has been moved by heap compaction.