[Octave-bug-tracker] [bug #56828] urlread/urlwrite/webread functions are not interruptible with Ctrl+C

[Kai Torben Ohlhus]

Follow-up Comment #2, bug #56828 (project octave):

Confirmed too.  As you observed in comment #1, this problem seems to be
related to the actual change of the macro
"BEGIN_INTERRUPT_IMMEDIATELY_IN_FOREIGN_CODE" to do effectively nothing at the
moment.

https://hg.savannah.gnu.org/hgweb/octave/file/60bb69799591/liboctave/util/quit.h#l196
https://hg.savannah.gnu.org/hgweb/octave/file/60bb69799591/liboctave/util/url-transfer.cc#l376

I grepped for all occurrences of this macro, and it is indeed only used for
urltransfer and some parse factorization functions.  Thus the damage is
limited, but also visible for the sparse functions, which are also not
stoppable, when inside the foreign code.


$ ./octave-4.2.2 --no-gui
GNU Octave, version 4.2.2
[...]
octave:1> [Q, R] = qr (sprand (10000, 10000, 1/10));
^C^CPress Control-C again to abort.

octave:1> exit

$ ./octave-4.4.1 
GNU Octave, version 4.4.1
[...]
octave:1> [Q, R] = qr (sprand (10000, 10000, 1/10));
^C^C^C
^C
octave:1>


Each ^C represents an attempt to stop the function.  On the other hand, the
following simplified C program can be stopped at any time by ctrl+c.


#include <curl/curl.h>

int main () {
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL,
     
"http://slowwly.robertomurray.co.uk/delay/10000/url/http://www.gnu.org/";);
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
  return 0;
}


Thus as you observed, Octave must be able to permit the external library to
detect ctrl+c again.  I need to get familiar with how Octave handles it
signals in this situation.


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