synchronized { }

[Steven Schveighoffer]

"cemiller" wrote
> On Thu, 26 Jun 2008 16:42:32 -0700, BCS wrote:
>
>> Reply to cemiller,
>>
>>> I use it on occasion. It can be useful for singleton:
>>>  if(!foo)
>>> {
>>> synchronized
>>> {
>>> if(!foo)
>>> foo = new Foo();
>>> }
>>> }
>>> return foo;
>>> especially useful because you don't need an object instance.
>>>
>>
>> Hmmm. Slight variation on my last suggestion, Allow synchronized to take 
>> any global symbol as the mutex
>>
>> if(!foo)
>> {
>>   synchronized(Foo)  // global mutex on Foo
>>   {
>>     if(!foo)
>>       foo = new Foo();
>>   }
>> }
>>
>> Or if you need more resolution:
>>
>> class Foo
>> {
>>   alias void single;
>> }
>>
>> ...
>>   synchronized(Foo.single)  // global mutex on Foo.single
>> ...
>
>
> I could synchronized(typeid(Foo)) but I don't think D guarantees that each 
> type has its own instance and monitor. This could potentially be a 
> substitute; create a type and lock on it, no runtime allocation, not many 
> language changes needed.

I think this is guaranteed as long as you are not loading D from multiple 
DLLs.

In any case, Tango avoids needing this statement by making mutexes fully 
accessible objects.  If you need a mutex without having it attached to an 
object, it's easy:

Mutex m = new Mutex;

synchronized(m)
{
}

-Steve