> On 17 Sep 2020, at 15:51, Dennis Lee Bieber <wlfr...@ix.netcom.com> wrote:
>
> On Wed, 16 Sep 2020 13:39:51 -0400, Alberto Sentieri <2...@tripolho.com>
> declaimed the following:
>
>
>> devices tested simultaneously, I soon run out of file descriptor. Well,
>> I increased the number of file descriptor in the application and then I
>> started running into problems like “ValueError: filedescriptor out of
>> range in select()”. I guess this problem is related to a package called
>
>
> https://man7.org/linux/man-pages/man2/select.2.html
> """
> An fd_set is a fixed size buffer.
> """
> and
> """
> On success, select() and pselect() return the number of file
> descriptors contained in the three returned descriptor sets (that
> is,
> the total number of bits that are set in readfds, writefds,
> exceptfds).
> """
> Emphasis "number of bits that are set" -- the two together implies that
> these are words/longwords/quadwords used a bitmaps, one fd per bit, and
> hence inherently limited to only as many bits as the word-length supports.
The limit has nothing to do with word size. The bits are passed as unsigned
char arrary.
Here is the piece expelling the limit:
select() can monitor only file descriptors numbers that are less than
FD_SETSIZE; poll(2) <https://man7.org/linux/man-pages/man2/poll.2.html>
and epoll(7) <https://man7.org/linux/man-pages/man7/epoll.7.html> do not have
this limitation. See
BUGS.
FD_SETSIZE is typically 1024.
Barry
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