Synchronized

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Mr B - 14 Mar 2007 16:38 GMT

In my application I have two methods which can be run by an infinite
number of threads, the operation of the method is to output an array
of contents one line at a time. If I use the keyword synchronized on
the Display1 method then this works fine and not the outputs get
interupted by the other Display1 threads, likewise with Display2. But
is there are way that just these two particular methods can also not
interrupt each other aswell? At the moment they are giving me mixed
up output from the two seperate methods.

Thanks
Daniel

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Gordon Beaton - 14 Mar 2007 16:45 GMT

> If I use the keyword synchronized on the Display1 method then this
> works fine and not the outputs get interupted by the other Display1
> threads, likewise with Display2. But is there are way that just
> these two particular methods can also not interrupt each other
> aswell? At the moment they are giving me mixed up output from the
> two seperate methods.

Instead of declaring the method synchronized, wrap the method body in
a synchronized block where you specify what object to synchronize on,
e.g.:

public void display() {
synchronized (obj) {
// do something here
}
}

Every block of code that synchronizes this way *and* specifies the
*same* obj will be mutually exclusive.

As was recommended elsewhere in this thread, I suggest you get
yourself a copy of Doug Lea's Concurrent Programming in Java.

/gordon

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[ don't email me support questions or followups ]
g o r d o n + n e w s @ b a l d e r 1 3 . s e

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Eric Sosman - 14 Mar 2007 16:49 GMT

Mr B wrote On 03/14/07 11:38,:

> In my application I have two methods which can be run by an infinite
> number of threads,

Impressive. How long does it take to start them all?

> the operation of the method is to output an array
> of contents one line at a time. If I use the keyword synchronized on
[quoted text clipped - 3 lines]
> interrupt each other aswell? At the moment they are giving me mixed
> up output from the two seperate methods.

Synchronize on the same object. When you write
`synchronized' at the start of a method or block of code,
it means `synchronized(this)' or `synchronized(theClassObj)'
for a static method. If Display1 and Display2 synchronize
on different objects, nothing prevents them from running
at the same time.

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Eric.Sosman@sun.com

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Ashoka! - 15 Mar 2007 04:17 GMT

> Mr B wrote On 03/14/07 11:38,:
>
[quoted text clipped - 20 lines]
> --
> Eric.Sos...@sun.com

Just to add instead of adding synchronized key word to the method use

void Display1(Object x, any other parameters)
{
Synchronize(x)
{

//code goes here

}
}

void Display2(Object x, any other parameters)
{
Synchronize(x)
{

//code goes here

}
}

where x is any object but both functions must get same instance of x
e.g.

void main()
{
String lock = "This is the common lock";
display1(lock);//obvously these two calls are synchronus but you get
my point of same instance right?
display2(lock);
}

also look at the sempahore class for much better control of multiple
threads.

I hope this helps,
Usman

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Synchronized

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