On Monday, 5 March 2018 at 19:51:33 UTC, Steven Schveighoffer wrote:
On 3/5/18 2:25 PM, Marc wrote:

Can __gshared be used instead of static in the singleton pattern? I, comming from C++, ignorantly, have never used _gshared so I went to static instead of (being static also means thread-safe, as far I know)...

static in D is thread safe, because it's thread-local. __gshared is shared between threads, so it's not thread safe, but has the exact same type as just static data.

Can you use it for singleton? Sure, classic singleton is shared between threads. But using thread-local data, you can solve the singleton problem in a better way:


Note, it still uses __gshared, which means it doesn't protect you from race conditions when you actually USE the singleton object. This means you need some synchronization inside the methods.


Singletons are always smelly code tbh.

Especially in D with thread-local storage.

I can't think of a situation where you truly need singletons in D.

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