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Guaranteed atomicity
Principle: Synchronized ensures that only one thread at a time acquires the lock and can access the synchronized code block.
Guaranteed visibility
Principle: When synchronized is executed, the corresponding lock atomic operation refreshes the value of the shared variable
Ensure order
Why reorder
To make the program more efficient, the compiler and CPU reorder the code in the program
The as – if – serial semantics
No matter how the compiler and CPU reorder, you must ensure that the program’s home country results are correct in the case of a single thread.
summary
With synchronized, reordering still occurs, except that we have synchronized code blocks that ensure that only one thread executes the code in synchronized code fast, thereby ensuring orderliness.
extension
Adding the volatile keyword before the num and ready shared variables also ensures order.