Re: [exim] data-phase efficiency

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Autor: Ian FREISLICH
Data:  
A: exim-users
CC: Jeremy Harris
Assumpte: Re: [exim] data-phase efficiency
Philip Hazel wrote:
> On Tue, 17 May 2005, Jeremy Harris wrote:
>
> > alarm(300)                              = 0
> > write(6, "mMR5AToGQBc3mGQLHkBBLmVYZAbZJ4iP"..., 8190) = 8190
> > alarm(0)                                = 300

> >
> > Could a select(or poll) for writability be used instead of
> > alarm, saving one syscall/cycle?
>
> I am a simple-minded programmer who likes to do things the easy way. As
> far as I can see, select() doesn't have an interface for asking "can I
> write 8190 bytes within 5 minutes?", which is what is needed here.


You need to do the following (non blocking descriptors rule):

    fcntl(s, F_SETFL, O_NONBLOCK);


    pollfd.fd = s
    pollfd.events = POLLWRNORM | POLLERR | POLLHUP | POLLNVAL;
do {
    read = fread(buffer,1,sizeof(buffer),spool_file);
    if (read > 0) {
        offset = 0;
again:
    result = poll(&pollfd, 1, 300);
    if (result == -1 && errno == EINTR)
        continue;
    else if (result < 1) {
        if (result == -1)
            log_write(0, LOG_MAIN|LOG_PANIC,
                "%s on connection", strerror(errno));
        else {
            log_write(0, LOG_MAIN|LOG_PANIC, "timed out writing");
        }
        goto bail;


    }
    if (pollfd.revents & (POLLERR | POLLHUP | POLLNVAL))
        goto bail;
    wrote = send(s,buffer + offset,read - offset,0);
    if (offset + wrote != read) {
        offset += wrote;
        goto again;
    }
}
while (!feof(spool_file) && !ferror(spool_file));


...

bail:
    // clean up.



Ian

--
Ian Freislich