'Re: Review Request 121710: Avoid risk of starting two kscreen_launchers at the same having race cond'

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List:       kde-panel-devel
Subject:    Re: Review Request 121710: Avoid risk of starting two kscreen_launchers at the same having race cond
From:       "David Edmundson" <david () davidedmundson ! co ! uk>
Date:       2015-01-02 11:20:08
Message-ID: 20150102112008.30561.22249 () probe ! kde ! org
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This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/121710/
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(Updated Jan. 2, 2015, 11:20 a.m.)

Status
------

This change has been marked as submitted.

Review request for Plasma, Solid and Daniel Vrátil.

Repository: libkscreen

Description
-------

Avoid risk of starting two kscreen_launchers at the same having a race condition.

There were three possible bugs:
CheckIsAlreadyRunning tried to register a service and check if it worked.
This could clash with another process checking at the same time. Causing them both to \
fail saying another is running Similarly, a daemon doing actual registering could \
clash with another daemon just checking if the name is free, and then it would fail \
saying we can't init()  
There was also a risk that two launchers pass the check that nothing is running, then \
both try to activate a session. DBus server handles this fine and one will gracefully \
fail. Without this patch the second launcher would just die without returning the \
path of the service that was activated causing the relevant app to do nothing.

--

IMHO, you'd be better off having a fixed service name and using DBus activation for \
exactly these reasons. You could put the different backends at different object \
paths, and have a method on the root object that says which object path to use rather \
than using the stdout of a launcher. That's a discussion for another day though.

Diffs
-----

  src/backendlauncher/backendloader.cpp e7da8cd 
  src/backendlauncher/main.cpp f8bf323 

Diff: https://git.reviewboard.kde.org/r/121710/diff/

Testing
-------

Send it to bshah. Plasmashell started for him. Previously it didn't.

Thanks,

David Edmundson

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      This is an automatically generated e-mail. To reply, visit:
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<div>Review request for Plasma, Solid and Daniel Vrátil.</div>
<div>By David Edmundson.</div>

<p style="color: grey;"><i>Updated Jan. 2, 2015, 11:20 a.m.</i></p>

<div style="margin-top: 1.5em;">
 <b style="color: #575012; font-size: 10pt;">Repository: </b>
libkscreen
</div>

<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
 <table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0">  <tr>
  <td>
   <pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Avoid risk of starting two kscreen_launchers at the \
same having a race condition.</p> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">There were three \
possible bugs: CheckIsAlreadyRunning tried to register a service and check if it \
worked. This could clash with another process checking at the same time. Causing them \
both to fail saying another is running Similarly, a daemon doing actual registering \
could clash with another daemon just checking if the name is free, and then it would \
fail saying we can't init()</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">There was also a risk that two \
launchers pass the check that nothing is running, then both try to activate a \
session. DBus server handles this fine and one will gracefully fail. Without this \
patch the second launcher would just die without returning the path of the service \
that was activated causing the relevant app to do nothing.</p> <p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">--</p> <p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">IMHO, you'd be better off having a fixed service name \
and using DBus activation for exactly these reasons. You could put the different \
backends at different object paths, and have a method on the root object that says \
which object path to use rather than using the stdout of a launcher. That's a \
discussion for another day though.</p></pre>  </td>
 </tr>
</table>

<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing </h1>
<table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" style="border: \
1px solid #b8b5a0">  <tr>
  <td>
   <pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Send it to bshah. Plasmashell started for him. \
Previously it didn't.</p></pre>  </td>
 </tr>
</table>

<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">

 <li>src/backendlauncher/backendloader.cpp <span style="color: \
grey">(e7da8cd)</span></li>

 <li>src/backendlauncher/main.cpp <span style="color: grey">(f8bf323)</span></li>

</ul>

<p><a href="https://git.reviewboard.kde.org/r/121710/diff/" style="margin-left: \
3em;">View Diff</a></p>

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