This was forbidden, but AndreyK points out cases in which LLParamSingleton::
initSingleton() should in fact be allowed to circle back to its own instance()
method. Use a recursive_mutex instead of plain mutex to permit that; remove
LL_ERRS preventing it.
Add LLParamSingleton::instance() method that calls
LLParamSingleton::getInstance(). Inheriting LLSingleton::instance() called
LLSingleton::getInstance() -- not at all what we want.
Add LLParamSingleton unit tests.
Simplify LLSingleton::SingletonLifetimeManager to SingletonInitializer: that
struct has not been responsible for deletion ever since LLSingletonBase
acquired dependency-ordered deleteAll().
Move SingletonData::mInitState changes from SingletonLifetimeManager to
constructSingleton() method. Similarly, constructSingleton() now sets
SingletonData::mInstance instead of making its caller store the pointer.
Add variadic arguments to LLSingleton::constructSingleton() so we can reuse it
for LLParamSingleton.
Add finishInitializing() method to encapsulate logic reused for
getInstance()'s INITIALIZING and DELETED cases.
Make LLParamSingleton a subclass of LLSingleton, just as LLLockedSingleton is
a subclass of LLParamSingleton. Make LLParamSingleton a friend of LLSingleton,
so it can access private members of LLSingleton without also granting access
to any DERIVED_CLASS subclass. This eliminates the need for protected
getInitState().
LLParamSingleton::initParamSingleton() reuses LLSingleton::constructSingleton()
and finishInitializing(). Its getInstance() method completely replaces
LLSingleton::getInstance(): in most EInitStates, LLParamSingleton::getInstance()
is an error.
Use a std::mutex to serialize calls to LLParamSingleton::initParamSingleton()
and getInstance(). While LLSingleton::getInstance() relies on the "initialized
exactly once" guarantee for block-scope static declarations, LLParamSingleton
cannot rely on the same mechanism.
LLLockedSingleton is now a very succinct subclass of LLParamSingleton -- they
have very similar functionality.
Giving the LLSINGLETON() macro variadic arguments eliminates the need for a
separate LLPARAMSINGLETON() macro, while continuing to support existing usage.
Nat Goodspeed