dbus_connection_send_with_reply_and_block eats 100% CPU then eventually times out

[Ralf Habacker]

Am 31.01.2015 um 13:08 schrieb Alex Brooks:
>
> Hi Ralf,
>
> Do you have a wlan0 on that computer?
>
no, wlp3s0 .. need to use -i i wlps3so
>
> (also note that the method in question (signalpoll)  is new in
> wpa_supplicant v2.3).
>
-> updated
+ need to run as root

> On 31 Jan 2015 19:27, "Ralf Habacker" <ralf at habacker.de
> <mailto:ralf at habacker.de>> wrote:
>
>
>     Am 31.01.2015 um 05:04 schrieb Alex Brooks:
>     > Hi,
>     >
>     > I've been fighting for a long time with what now looks like a
>     libdbus
>     > bug.
>     > I have a cut-down test program which calls a dbus method of
>     > wpa_supplicant at 100Hz, it does this happily for several hours then
>     > at some point the behaviour changes: any future calls sit at
>     100% CPU
>     > for 25sec then time out.
>
who eat's the cpu
- dbus-daemon
- wpa_supplicant
- your client app
>
>     > I don't think the problem is on the wpa_supplicant side: other
>     clients
>     > can simultaneously make this call without any problems, and
>     restarting
>     > the client fixes it.
>
you did a strace of the related processes ?
>
>     > [I'm running at 100Hz because the faster I run this loop, the
>     faster> it reproduces the problem.  CPU load sits below 20% before
>     I hit the
>     > bug].
>
the test case contains

    while ( true )  {
...
      usleep(0.1 * 1e6);
   }

which is 10H z

got it running as root

Ralf
>
>     >
>     > I posted details and a sample program as a Qt bug report (I'm using
>     > the QDBus wrapper and thought it might be a Qt bug initially):
>     > https://bugreports.qt.io/browse/QTBUG-43550
>     >
>     > Does anyone have any thoughts?
>     I compiled the testcase on opensuse 13.1 x86_64 and did run:
>
>     sudo ./signalpoll
>     getNetDevObjectPath(wlan0)
>     getNetDevObjectPath : GetInterface result:  QDBusMessage(type=Error,
>     service="", error name="fi.w1.wpa_supplicant1.InterfaceUnknown", error
>     message="wpa_supplicant knows nothing about this interface.",
>     signature="", contents=([]) )
>     terminate called after throwing an instance of 'std::string'
>
>     Regards
>      Ralf m
>

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