Function IntrusivePtr.compareExchangeStrong

Compares the IntrusivePtr pointers pointed-to by this and expected.

bool compareExchangeStrong(MemoryOrder success = MemoryOrder.seq, MemoryOrder failure = success, E, D, This) (
  scope ref E expected,
  scope D desired
) scope
if (isIntrusivePtr!E && !is(E == shared) && isIntrusivePtr!D && !is(D == shared) && (isMoveConstructable!(D, This) && isMutable!This) && (isCopyConstructable!(This, E) && isMutable!E) && (This.isWeak == D.isWeak) && (This.isWeak == E.isWeak));

If they are equivalent (store the same pointer value, and either share ownership of the same object or are both empty), assigns desired into this using the memory ordering constraints specified by success and returns true. If they are not equivalent, assigns this into expected using the memory ordering constraints specified by failure and returns false.

More info in c++ std::atomic.

Examples

static class Foo{
    long i;
    ControlBlock!(int, int) c;

    this(long i)pure nothrow @safe @nogc{
        this.i = i;
    }

    bool opEquals(this This)(long i)const @trusted{
        import std.traits : Unqual;
        auto self = cast(Unqual!This)this;
        return (self.i == i);
    }


}
alias Type = Foo;
static foreach(enum bool weak; [true, false]){
    //fail
    {
        IntrusivePtr!Type a = IntrusivePtr!Type.make(123);
        IntrusivePtr!Type b = IntrusivePtr!Type.make(42);
        IntrusivePtr!Type c = IntrusivePtr!Type.make(666);

        static if(weak)a.compareExchangeWeak(b, c);
        else a.compareExchangeStrong(b, c);

        assert(*a == 123);
        assert(*b == 123);
        assert(*c == 666);

    }

    //success
    {
        IntrusivePtr!Type a = IntrusivePtr!Type.make(123);
        IntrusivePtr!Type b = a;
        IntrusivePtr!Type c = IntrusivePtr!Type.make(666);

        static if(weak)a.compareExchangeWeak(b, c);
        else a.compareExchangeStrong(b, c);

        assert(*a == 666);
        assert(*b == 123);
        assert(*c == 666);
    }

    //shared fail
    {
        shared IntrusivePtr!(shared Type) a = IntrusivePtr!(shared Type).make(123);
        IntrusivePtr!(shared Type) b = IntrusivePtr!(shared Type).make(42);
        IntrusivePtr!(shared Type) c = IntrusivePtr!(shared Type).make(666);

        static if(weak)a.compareExchangeWeak(b, c);
        else a.compareExchangeStrong(b, c);

        auto tmp = a.exchange(null);
        assert(*tmp == 123);
        assert(*b == 123);
        assert(*c == 666);
    }

    //shared success
    {
        IntrusivePtr!(shared Type) b = IntrusivePtr!(shared Type).make(123);
        shared IntrusivePtr!(shared Type) a = b;
        IntrusivePtr!(shared Type) c = IntrusivePtr!(shared Type).make(666);

        static if(weak)a.compareExchangeWeak(b, c);
        else a.compareExchangeStrong(b, c);

        auto tmp = a.exchange(null);
        assert(*tmp == 666);
        assert(*b == 123);
        assert(*c == 666);
    }
}