Writing a unit test for a singleton implementation

[Idan Arye]

I'm making an idioms 
library(http://forum.dlang.org/thread/fofbrlqruxbevnxchxdp@forum.dlang.org) 
to add to Phobos, and one of the idioms is the singleton design 
pattern. Since I'm gonna send it to Phobos, it needs to have a 
unit test. Here is my unit test:

     static class Foo
     {
         mixin LowLockSingleton;

         this()
         {
             Thread.sleep(dur!"msecs"(500));
         }
     }

     Foo[10] foos;

     foreach(i; parallel(iota(foos.length)))
     {
         foos[i] = Foo.instance;
     }

     foreach(i; 1 .. foos.length)
     {
         assert(foos[0] == foos[i]);
     }


This unit test works - it doesn't fail, but if I remove the 
`synchronized` from my singleton implementation it does fail.

Now, this is my concern: I'm doing here a 500 millisecond sleep 
in the constructor, and this sleep is required to guarantee a 
race condition. But I'm not sure about two things:

  - Is it enough? If a slow or busy computer runs this test, the 
500ms sleep of the first iteration might be over before the 
second iteration even starts!

  - Is it too much? Phobos has many unit tests, and they need to 
be run many times by many machines - is it really OK to add a 
500ms delay for a single item's implementation?


Your opinion?