Computed vars do not write to invocation array in a threadsafe way

[welshm]

    public var currentDate: Date {
		get {	invocations.append(.p_currentDate_get); return __p_currentDate ?? givenGetterValue(.p_currentDate_get, "CurrentDateProviderMock - stub value for currentDate was not defined") }
	}

whereas functions do

    open func cancelTrigger() {
        addInvocation(.m_cancelTrigger)
		let perform = methodPerformValue(.m_cancelTrigger) as? () -> Void
		perform?()
    }