Re: Volatile happens before question
On 1/17/2012 8:49 AM, Knute Johnson wrote:
On 1/17/2012 8:33 AM, markspace wrote:
On 1/17/2012 8:18 AM, Knute Johnson wrote:
Does this work in reverse too?
For example,
Thread 1
int b = 0;
volatile boolean a = false;
...
...
a = true;
b = 1;
Thread 2
int bStore = b;
if (!a) {
System.out.println("The value of b is " + bStore);
}
Will this always print either "The value of b is 0" or nothing.
Yes
I'm pretty sure Peter got the correct answer which is "no." I want to
stick my answers in a separate reply, so I'll just add that this is an
easy mistake to make and if both Peter and you hadn't already provided
some insights I probably would have flubbed it up myself.
Reasoning about synchronization can be pretty hard. Make sure you
consider carefully all possibilities when analyzing multi-threaded
programs for bugs.
OK, I'll bite, if a is false how can b be anything but 0?
And if b = 1 could be reordered before a = true then b would be flopping
all over the place because as soon as a = true b would again have to be 0.
--
Knute Johnson
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