The big power of multithreaded programming lies in the fact that all threads can access all the memory in the program. When we create a new thread that will process some program data, we don't need any special preparations. We just create the thread and that data will be available to it.
This, however, is also the biggest weakness of multithreaded programming. If multiple threads are accessing the same data, they can easily interfere with each other. One thread can overwrite the data of another thread or it can modify the structure that another thread is using. This results in all kinds of problems, including random crashes at unexpected locations.
As an example, imagine this situation. A first thread is walking some list and processing elements with the following code:
for i := 0 to FList.Count - 1 do
DoSomethingWith(FList[i]);
FList is a global object and...