The usual pattern for a singleton class is something like\
static Foo &getInst()
{
static Foo *inst = NULL;
if(inst == NULL)
inst = new Foo(...);
return *inst;
}
However, it's my understanding that this solution is not thread-safe, since 1) Foo's constructor might be called more than once (which may or may not matter) and 2) inst may not be fully constructed before it is returned to a different thread.
One solution is to wrap a mutex around the whole method, but then I'm paying for synchronization overhead long after I actually need it. An alternative is something like
static Foo &getInst()
{
static Foo *inst = NULL;
if(inst == NULL)
{
pthread_mutex_lock(&mutex);
if(inst == NULL)
inst = new Foo(...);
pthread_mutex_unlock(&mutex);
}
return *inst;
}
If you are using C++11, here is a right way to do this:
Foo& getInst()
{
static Foo inst(...);
return inst;
}
Suggest if better methods available?
static Foo &getInst()
{
static Foo *inst = NULL;
if(inst == NULL)
inst = new Foo(...);
return *inst;
}
However, it's my understanding that this solution is not thread-safe, since 1) Foo's constructor might be called more than once (which may or may not matter) and 2) inst may not be fully constructed before it is returned to a different thread.
One solution is to wrap a mutex around the whole method, but then I'm paying for synchronization overhead long after I actually need it. An alternative is something like
static Foo &getInst()
{
static Foo *inst = NULL;
if(inst == NULL)
{
pthread_mutex_lock(&mutex);
if(inst == NULL)
inst = new Foo(...);
pthread_mutex_unlock(&mutex);
}
return *inst;
}
If you are using C++11, here is a right way to do this:
Foo& getInst()
{
static Foo inst(...);
return inst;
}
Suggest if better methods available?