On 05/11/2012 10:30 AM, Jacopo Cappellato wrote:
> On May 11, 2012, at 4:51 PM, Adam Heath wrote:
>
>> ==
>> result = parsedScripts.get(key)
>> if (result == null) {
>> syncyronized (parsedScripts) {
>> result = parsedScripts.get(key)
>> if (result == null) {
>> result = genResult()
>> parsedScripts.put(key, result)
>> }
>> }
>> }
>> return result
>> ==
>>
>> DCL is about the protected resource, parsedScripts. Please try again.
>>
>> The clue here it to look at what is being protected by the
>> synchronized keyword.
>
> Just to be sure I understand: are you saying that the above code is an
> example of the DCL anti-pattern and it is wrong?
I'm not saying that. Others are saying that, and I'm just repeating it.
http://en.wikipedia.org/wiki/Double-checked_locking
==
class Foo {
private Helper helper = null;
public Helper getHelper() {
if (helper == null) {
synchronized(this) {
if (helper == null) {
helper = new Helper();
}
}
}
return helper;
}
// other functions and members...
}
==
In my example, the protected variable is parsedScripts(instead of
this), the get/put on the map is setting the variable on the class.
