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From "Saxon" <sa...@saxon.cx>
Subject apr_poll_setup
Date Sat, 23 Mar 2002 07:37:18 GMT
Hi,

I was wondering about the 'num' parameter of apr_poll_setup(). The header
(apr_network_io.h) says it's "The number of socket descriptors to be
polled".

However, in win32's poll.c apr_poll_setup() first allocates num
apr_pollfd_t's, then sets values in the first apr_pollfd_t, ie allocates an
fd_set for each of read, write and except. After that, it's only the
fd_set's in the first apr_pollfd_t that get used. In winsock2.h the fd_set
is defined as:

typedef struct fd_set {
    u_int fd_count;                 /* how many are SET? */
    SOCKET  fd_array[FD_SETSIZE];   /* an array of SOCKETs */
} fd_set;

FD_SETSIZE defaults to 64, but can be set to a different value before
including winsock2.h, and it will use that. So, the actual number of sockets
which can be polled is 64. The num parameter to apr_poll_setup() is ignored,
except for allocating some wasted memory.

I had a quick look at unix's poll.c, and the version which uses select (ie
if HAVE_POLL is zero) does much the same thing. I had a look through the
headers on my Linux machine, and while fd_set is a different structure, it
also contains space for a fixed number of sockets, but this time the limit
is 1024.

Or maybe I've missed the point entirely :)

This is all based on a cvs snapshot I downloaded yesterday, called
apr_20020322112848.tar.gz.

bye,
Saxon



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