الرؤية وعلاقة happens-before

في هذا الدرس

explain why a thread may not see another's write.

الموضوعات المخطط لها

• CPU caches and compiler reordering mean a write may not be visible to other threads.
• The Java Memory Model defines happens-before: if A happens-before B, B sees A's writes.
• Practical edges: unlock then lock of the same monitor; write then read of a volatile; Thread.start() and join(); executor submit then task run, and task completion then Future.get().
• Without such an edge, a loop on a plain flag may never stop.
• Visibility and atomicity are different problems.