Re: what is the point of volatile?
Lew wrote:
apm35@student.open.ac.uk wrote:
Can anyone tell me what the value is of 'volatile' please? It seems to
me to be a lazy way of protecting a private data member without having
to write a synchronized getter and setter. But it only works for types
that can be updated atomically. This sounds a bit tricky to me....
The point of volatile is to provide a kind of lightweight synchronization.
I don't know why you call it "lazy". Nor is it limited to private
members; volatility is orthogonal to access.
Reads from a volatile member are guaranteed to see previous writes to
that variable. In fact, reads from a volatile variable guarantee that
all writes prior to the latest write to that variable are visible. This
is not so for non-volatile variables. That is the new (as of 5) memory
model for Java.
It's worth pointing out that volatile doesn't mean atomic:
volatile int a;
++a; // Still two separate accesses to a
I didn't fully understood volatile until I read about it in the book
Java Concurrency In Practice
<http://virtualinfinity.net/wordpress/technical-book-recommendations/java-concurrency-in-practice/>
The only real use I've found for it is for a simple
you-should-shut-down-now flag to a tight-looped thread. That thread
only needs to read, and other threads only need to write.
--
Daniel Pitts' Tech Blog: <http://virtualinfinity.net/wordpress/>