访问列表项时，UI和辅助线程同步

Question

I have a List which has data to process. And I have 2 threads,

UI Thread : Updates/Adds the List item,

Thread 1 : Once item added into list it sends the item one by one to another thread 2,

Thread 2 : Does it's work and updates the item accordingly and Once it completes it's work, it checks list and if the corresponding item still exists in the list, If it exists it process the data.

From UI thread when closing the window, I am removing the items from map which are added from the UI. So that the thread 2 won't proceed the items which are removed from list.

And from the UI destruct or, I am deleting the item instances which are added in list.

The issue is, Thread 2 is already processing an item, In the mean time Window is closed and also the destructor deleted the item which is in processing by thread 2.

So the processing of the data by the thread 2 crashes.

I have done this in MFC. How to synchronize these 2 threads (UI deletion and Thread 2). I know there are different Thread synchronization methods in MFC. Which method is best for this scenario?

Answer 1

When you want to halt the operation (perhaps when the user clicks the Close button), first you tell the thread to exit. That can be done with a bool or a event (SetEvent) that the thread checks regularly. After you tell the thread to exit you must not delete the UI or any data being used by thread until you are sure the thread has exited. Use the thread handle in WaitForSingleObject to wait for the thread to exit. WaitForSingleObject suspends the calling thread until the thread handle signals that the thread has exited. Then you can continue the delete and UI shutdown.