in cxx/fbjni/detail/CoreClasses-inl.h [485:498]
static void allocate(
alias_ref<typename jtype_traits<T>::array_type> array,
jsize start,
jsize length,
T** elements,
size_t* size,
jboolean* isCopy) {
(void)start;
(void)length;
const auto env = Environment::current();
*elements = static_cast<T*>(env->GetPrimitiveArrayCritical(array.get(), isCopy));
FACEBOOK_JNI_THROW_EXCEPTION_IF(!elements);
*size = array->size();
}