imageSourceThumbnailOptions() is called to build the dictionary of the async image decoding options. It uses the static variable `options` which is initialized the first time this function is called. If this function is called from multiple threads at the same time, more than one thread can see that the static variable `options` is initialized and may initialize it then. Setting the variable from these threads are not be atomic. So we may be end up with invalid pointer for this static variable.