c++ - Some doubts about operator new() and handles in msvc?

Question

void* __CRTDECL operator new(size_t const size)
{
    for (;;)
    {
        if (void* const block = malloc(size))
        {
            return block;
        }

        if (_callnewh(size) == 0)
        {
            if (size == SIZE_MAX)
            {
                __scrt_throw_std_bad_array_new_length();
            }
            else
            {
                __scrt_throw_std_bad_alloc();
            }
        }

        // The new handler was successful; try to allocate again...
    }
}

I know that this endless loop is to wait for the memory to be allocated successfully and then return the pointer. However, my operating system knowledge is very weak (non-major), so I would like to ask everyone about the endless loop here. How is the second if of analyzed (such as the processing of the handle here, etc.).

Thanks

Answer 1

_callnewh will call a handle to handle memory allocation failure. This handle can try to release some memory or wait for a period of time or directly throw an exception?. If the handle call returns _callnewh(size) != 0，那么new会再一次尝试申请，如果调用失败_callnewh(size) == 0 successfully, the relevant exception is thrown.

if (size == SIZE_MAX)说明申请的对象数太多（size_t理论上能表达任何对象的数量）。elseIt is a general application failure. std_bad_array_new_length and std_bad_alloc refer to the corresponding exceptions in the standard library.

Related interface: _set_new_handler