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Core issues of JAVA concurrency overview

It is not caused by the loophole in the program, but by the underlying mechanism of the operating system.

Atomicity:

Visibility issues:

The cache is changed, but the cache is not visible to another thread

The question of order:

Normally, the object should be created first, and then assigned; the compiler optimizes the instruction execution order for some reason, and then changes the execution order, as follows:

Solution

Visibility:

Order:

This principle takes effect automatically when volatile and lock are added, that is, visibility and atomicity are solved, and visibility is solved incidentally.

Atomicity:

From the operating system point of view, the name of the monitor is pipe program.

If the problem of atomicity is solved, both visibility and order can be solved.

Concurrent tool

There will be an ABA problem in the way of CAS, that is, it has been modified twice and changed back to the original value, but the check has not changed. There will be a problem with the referenced object. The address of the referenced object has not changed, but the referenced things have changed.

Other options

ThreadLocal, the thread is the Key, and the value is the thread's data. Each thread takes things and stores things, which are separated by the thread key.

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