Some objects have built-in locking that prevents the execution of other threads from using that object instance.
For example, canvas objects (TCanvas and descendants) have a Lock method that prevents other threads from accessing the canvas until the Unlock method is called.
The VCL also includes a thread-safe list object, TThreadList. Calling TThreadList::LockList returns the list object while also blocking other execution threads from using the list until the UnlockList method is called. Calls to TCanvas::Lock or TThreadList::LockList can be safely nested. The lock is not released until the last locking call is matched with a corresponding unlock call in the same thread.
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