Java - use of volatile only makes sense in multiprocessor systems?

Use of volatile only makes sense in multiprocessor systems. is this wrong?

i'm trying to learn about thread programming, so if you know any good articles/pdfs 开发者_如何学Python... i like stuff that mentions a bit about how the operating system works as well not just the language's syntax.

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No. Volatile can be used in multi-threaded applications. These may or may not run on more than one processor.

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volatile is used to ensure all thread see the same copy of the data. If there is only one thread reading/writing to a field, it doesn't need to be volatile. It will work just fine, just be a bit slower.

In Java you don't have much visibility as to the processor architecture, generally you talk in terms of threads and multi-threading.

I suggest Java Concurrency in Practice, it good whatever your level of knowledge, http://www.javaconcurrencyinpractice.com/

The whole point of using Java is you don't need to know most of the details of how threads work etc. If you learn lots of stuff you don't use you are likely to forget it. ;)

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Volatile makes sense in a multithreaded programm, running these threads on a single processor or multiple processors does not make a difference. The volatile keyword is used to tell the JVM (and the Java Memory Model it uses) that it should not re-order or cache the value of a variable with this keyword. This guarantees that Threads using a volatile variable will never see a stale version of that variable.

See this link on the Java Memory Model in general for more details. Or this one for information about Volatile.

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No. Volatile is used to support concurrency. In certain circumstances, it can be used instead of synchronization.

This article by Brian Goetz really helped me understand volatile. It has several examples of the use of volatile, and it explains under what conditions it can be used.