On Saturday, 18 May 2013 at 16:58:19 UTC, Idan Arye wrote:
OK, I implemented everything and made a pull request: https://github.com/D-Programming-Language/phobos/pull/1294
Nice, but the singleton implementation seems somewhat over-complicated, and the low-lock singleton is broken, possibly as a result of the former problem.
You need two variables of type T (assuming T is the target class). One should be __gshared, the other thread-local. When "instance()" is called, first check if the thread-local variable is non-null, if so just return it. Otherwise enter a synchronized block, check if the __gshared variables is null (and if so initialise it) then copy its value to the thread-local variable and finally return it.
For a "hasInstance" method to make any sense, the caller must be able to synchronize on the same object that "instance()" uses to synchronize on when it accesses the __gshared variable. Otherwise the return value is out of date before it's even been returned.
