Threads and local variables

[Carlos G�mez]

Hi ranchers

why the local variables are thread safe ??

Thanks in advance.

[Henry Wong]

Originally posted by Carlos G�mez:
Hi ranchers

why the local variables are thread safe ??

Thanks in advance.

Local variables are private to the method -- every method calls gets their own copy. Hence, every thread that calls a method, will get their own copy.

Note: they may *not* be thread safe. It is possible to assign an object reference (that is a local variable) to a shared object. While changing the local reference variable is threadsafe, changing the shared object that it refers to, may not be.

Henry

[bala nannaka]

Every thread is associated with one thread context . that is nothing but a stack .in which all the local variables are stored.so every thread has its own thread context so there is a no problem for thread safety

[Stan James]

Let's open up Henry's point with a couple examples. Here the local variable map is pretty safe because we create the map locally, use it locally and don't let anybody else see it.

public void doSomething()
{
   Map localMap = new HashMap(); 
   do something with the map
}

But in the next one, we don't know who else might be using the map object. The object that passed it in to us may be using it on another thread. So just assigning it to a local variable won't help make it safe.

public void doSomething( Map map )
{
   Map localMap = map;
   do something with map
}

And in this next one, we expose the map to somebody else who might do something unsafe with it:

public void doSomething()
{
   Map localMap = new HashMap();
   otherObject.someMethod( localMap );
   do somethign with map
}

So a local variable is only safe if we keep it local.

[Carlos G�mez]

yeah, thank you ranchers !!