Re: transactions stall after March 6 commit to improve wakeup and wait code in multi

> >> Any chance you can for example modify an existing example source code to 
> >> reproduce this behavior? Then we would have a good reproducer to work with!
> 
> I'll see what I can do. 

This might be easier than I thought to reproduce.

I use an easy handle with no options set whatsoever, not even a URL.
Apparently, this is legal and just means performing the transaction is a
no-op.  At least that's what Curl did before that March commit.

But following the commit, if I add that handle to a multi manager,
'curl_multi_fdset' says there is a file descriptor which I have to wait for to
become ready before that transaction can proceed, and that file descriptor
never becomes ready.

I don't know where to find a published example of using curl_multi_fdset to
use as a reproducer, but I made a very simple one that must look a lot like
any such example.  Code is below.

When I run this against old libcurl, it prints, "There are no file descriptors
to wait for" and exits.  With new libcurl, it prints, "libcurl supplied a file
descriptor [...] waiting now ..." and then hangs.

-------------------------------------------------------------------------------
#include <assert.h>
#include <stdio.h>
#include <sys/select.h>

#include <curl/curl.h>
#include <curl/easy.h>
#include <curl/multi.h>

int
main(int , const char ** ) {

    CURLMcode rc;

    printf("Hello world.\n");

    CURL * const curlSessionP = curl_easy_init();

    assert(curlSessionP);

    CURLM * const curlMultiP = curl_multi_init();

    assert(curlMultiP);

    rc = curl_multi_add_handle(curlMultiP, curlSessionP);

    assert(rc == CURLM_OK);

    fd_set readFdSet, writeFdSet, exceptFdSet;
    int maxFd;

    rc = curl_multi_fdset(curlMultiP,
                          &readFdSet, &writeFdSet, &exceptFdSet,
                          &maxFd);

    assert(rc == CURLM_OK);

    if (maxFd == -1)
        // With libcurl 8.19, this is the case.
        fprintf(stderr, "There are no file descriptors to wait for\n");
    else {
        fprintf(stderr, "libcurl supplied a file descriptor to "
                "wait for (maxFd=%u).  Waiting now ...\n", maxFd);

        pselect(maxFd + 1, &readFdSet, &writeFdSet, &exceptFdSet,
                NULL /* timeout */, NULL /* signal mask */);

        // Problem: This 'pselect never completes

        fprintf(stderr, "A file descriptor is ready.\n");
    }

    return 0;
}
-------------------------------------------------------------------------------



--
Bryan Henderson                                   Omak, Washington
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