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<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">Hello folks,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">we’re facing the following issue:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">An application does not receive DBUS signals via the DBUS file descriptor while waiting for a dbus-method response.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">The basic setup: Two applications are communicating via DBUS, using a
<b>select() loop waiting for events on the</b> <b>dbus-fd</b>.<br>
The faulty procedure:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo10">
<![if !supportLists]><span lang="EN-US" style="font-size:11.0pt;line-height:110%"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="font-size:11.0pt;line-height:110%;color:#009759">Triggered by a timer event, Application A</span><span lang="EN-US" style="font-size:11.0pt;line-height:110%"> calls the dbus-method “transmit” of
<span style="color:#F6960F">application B</span>.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo10">
<![if !supportLists]><span lang="EN-US" style="font-size:11.0pt;line-height:110%"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="font-size:11.0pt;line-height:110%">During processing of the “transmit”-method,
<span style="color:#F6960F">application B</span> broadcasts a dbus-signal on which
<span style="color:#009759">application A</span> is matched on.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo10">
<![if !supportLists]><span lang="EN-US" style="font-size:11.0pt;line-height:110%"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="font-size:11.0pt;line-height:110%">Afterwards,
<span style="color:#F6960F">application B</span> sleeps for 5ms and then finishes its “transmit”-method by sending a response message towards
<span style="color:#009759">application A.</span><o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l1 level1 lfo10">
<![if !supportLists]><span lang="EN-US" style="font-size:11.0pt;line-height:110%"><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="font-size:11.0pt;line-height:110%">The dbus-fd of
<span style="color:#009759">Application A</span> does not trigger the <b>select() afterwards</b> (same for
<b>epoll() </b>if implemented so).<br>
Though …<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l1 level2 lfo10">
<![if !supportLists]><span lang="EN-US" style="font-size:11.0pt;line-height:110%;font-family:"Courier New""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="font-size:11.0pt;line-height:110%">… when triggering
<b>sd_bus_process() </b>manually, the signal is being receved in <span style="color:#1F497D">
a</span>pplication A, meaning that the signal was in fact received and queued, but the event was not signalled.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:72.0pt;text-indent:-18.0pt;mso-list:l1 level2 lfo10">
<![if !supportLists]><span lang="EN-US" style="font-size:11.0pt;line-height:110%;font-family:"Courier New""><span style="mso-list:Ignore">o<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US" style="font-size:11.0pt;line-height:110%">… other processes, not being “blocked” by waiting for a response-message, do also receive the signal.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">We saw this behavior on multiple platforms, e.g. Linux kubuntu 4.4.0-137-generic with 229-4ubuntu21.1 and Debian Buster 4.18.0-2-am64 with systemd 239-10.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">Attached you can find a simple example, including application
<span style="color:#009759">A</span> / <span style="color:#F6960F">B</span>, a makefile and the correlating *.conf-files.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">Thanks in advance<span style="color:#1F497D"> and
</span>best regards, <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;line-height:110%">Jan Mueller<span style="color:#1F497D"><o:p></o:p></span></span></p>
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