Sounds good to me.
El 14/02/2013 1:46, KIU Shueng Chuan escribió:
Are we okay with using assertions to catch both
- programming errors
- rare but known situations not handled in the code? (in this case
resource exhaustion)
How about this: Have make_fdpair() return -1 (and release the critical
section) on error returns from the calls to connect() and accept() only.
The failure will be caught by signaler_t() which calls make_fdpair()
On Wed, Feb 13, 2013 at 7:22 PM, Pau <[email protected]
<mailto:[email protected]>> wrote:
Hi, thanks
I do not want to look bungler, but wouldn't be a shortcut to
implement asserts that clean the event before aborting?
El 13/02/2013 9:54, KIU Shueng Chuan escribió:
Hi Pau,
The system-wide critical section is currently implemented using a
win32 Event which, as you observed, has the possibility of
resulting in a deadlock in the following situation:
1) Process A takes the Event
2) Process B tries to take the Event and blocks
3) Process A aborts within the critical section (due to an
assertion being raised)
4) Since Process B has opened the Event, the OS will not clean up
the Event.
5) Process B and any subsequent process will now block forever
for the Event.
As I mentioned in the previous mail, if the critical section were
to be implemented using a Mutex instead, then in step 5, Process
B would be able to enter the critical section with a return code
of WAIT_ABANDONED from WaitForSingleObject. (Or at least that's
what I read from MSDN)
Note: If Process A aborted due to some exhaustion of resources,
then Process B would likely hit the same assertion too.
The question is how to convert the Event to a Mutex and yet not
break compatibility with existing applications using older
versions of the library.
On Wed, Feb 13, 2013 at 3:28 PM, Pau <[email protected]
<mailto:[email protected]>> wrote:
Hi,
I am back with the asserts happening inside a critical
section in signaler.cpp.
The problem still is that in signale.cpp make_fdpair(..)
creates system-wide critical section and does a number of
things that can generate a wsa_assert() or win_assert()
before releasing the session.
I have seen that in the trunk someone has added a
CloseHandle(sync) at the end of the function, I do not know
if it had something related with this but I understand that
the problem is still there. wsa_assert() and wsa_windows()
end up in RaiseException (0x40000015,
EXCEPTION_NONCONTINUABLE, 1, extra_info) which I understand
is a cul de sac that has no way out to clean up before leaving.
I guess we need a special assert function to use inside this
critical but I'd like a more documented opinion (Kiu?).
thanks,
Pau Ceano
El 21/01/2013 23:37, KIU Shueng Chuan escribió:
Hi Pau, a fix for the assertion on connection to port 5905
is in trunk branch.
I think the dangling critical section possibility could be
fixed by changing the Event to a Mutex. When an assertion
occurs the mutex would just be abandoned. However this
change will cause backward compatibility issues with older
versions.
On Jan 22, 2013 2:04 AM, "Pieter Hintjens" <[email protected]
<mailto:[email protected]>> wrote:
Hi Pau,
So there are two different problems here, one is that
we're hitting a
socket limit on WXP, and the other is that the asserts
are happening
inside a critical section.
I don't think we can fix the first one easily but we can
presumably
assert in a smarter way. Do you want to try making a
patch for this?
-Pieter
On Mon, Jan 21, 2013 at 6:23 PM, Pau <[email protected]
<mailto:[email protected]>> wrote:
>
> Hi,
>
>
> I am using (not yet in production) ZMQ on Windows and
I have found what
> I think is a big problem for Windows users.
> We use WXP and W7 and Visual C++ different versions.
ZMQ version 3.2.0
> (as far as I see the same problem happens in 3.2.2)
>
> I do not fully understand ZMQ internals but I've seen
that every time a
> socket is created the function make_fdpair(..) is
called and in
> signaler.cpp(line244) a system event
"zmq-signaler-port-sync" is created.
> This event is used as a system-wide critical section
and, so all
> applications that try to create an event will
WaitForSingleObject (sync,
> INFINITE) until SetEvent (...) is called.
> The problem is that the code between:
> HANDLE sync = CreateEvent (NULL, FALSE, TRUE, TEXT
> ("zmq-signaler-port-sync"));
> and
> SetEvent (sync);
> is full of wsa_asserts(..) that will terminate the
application if
> something goes wrong.
>
> It is clear that terminating the application not
leaving the system-wide
> critical section is a bad idea because all
applications in the system
> will hang and you will have to stop all them to start
again.
> I understand that no errors should happen but anyway
to escape from the
> error is not a good idea in this case.
>
> I do not know all possible reasons to generate a fatal
wsa_assert(..)
> but there is at least one:
>
> I have seen that in XP it is possible that line 301
rc = connect (*w_,
> (sockaddr *) &addr, sizeof (addr)); returns an error
when a socket tries
> to connect to 5905 and this has happened many times.
> Windows uses port numbers starting near 1400 and XP
has a limit at 5000.
> In W7 this does not look as a problem because maximum
is 65000
> It sounds as if the number was big enough but apart
from the fact that
> ZMQ uses a big number of connections (at least in my
tests) I have
> experienced that Windows jumps port numbers by 7, so
5000 happens
> sometimes with catastrophic consequences.
>
> best,
>
> Pau Ceano
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