[zeromq-dev] Assertion failed: nbytes == sizeof (command_t) (mailbox.cpp:246) during orderly shutdown.

[Mike Pearce]

♫
Hi,

Thanks for your emails regard this.

I attach a test that creates the error. Unfortunately the error is part of a
race condition and I found that it occurs more frequently if
zmq::mailbox_t::recv function can loop faster. I added a debug output to
show when nbytes==0 but this reduced the error frequency and so I added
another debug which skips this additional test for the most common condition
(i.e. nbytes==sizeof(command_t)). This means that the bottom of the function
now looks like :

#endif
if (nbytes == sizeof (command_t)) return 0;   // I added this as a quicker
exit for the code
    //  Sanity check for success.
    errno_assert (nbytes != -1);
if (nbytes!= sizeof (command_t)) printf("nbytes=%d\n",nbytes);  // Here I
test and output my printf in the case where the error occurs
    //  Check whether we haven't got half of command.
    zmq_assert (nbytes == sizeof (command_t));

    return 0;

If you prefer then you do not need to add any additional statements for the
error to occur but I found this debug output rather useful.

Sorry also that the test is using QT. I am guessing that QT is making a big
difference regard this race condition and so I am not sure of any advantage
to remove it,

I am also seeing a much worse problem and when you run the test you may also
see this. zmq_term hangs in mailbox which is awaiting the reaper thread to
clean up but it never comes back and so nothing exits. I have yet to
understand what is happening as I need to also avoid this problem but I do
not have sufficient information yet to be able to report the issue. If you
have any ideas on this fault then it will also be most helpful.

Thanks,

Mike.
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