What difficulties may arise if all threads work with a shared global variable?

If multiple threads work with a shared global variable without synchronization, the following problems can occur:

• Data races — when two threads read and write to the variable simultaneously, resulting in unpredictable outcomes.
• Unpredictable program behavior — due to data inconsistency.
• Visibility issues — one thread may not see updates made by another.
• Errors and crashes — for example, data structure corruption.

To prevent these problems, synchronization mechanisms are used: locks (mutex), atomic operations, message queues, or other access control tools.