Re: Session file locking not working properly in multithreaded environment

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On Friday, 10 May 2019 19:31:28 UTC+2, Tim Roberts wrote:
>
>
> The zc.lockfile I'm looking at certainly opens a new fd each time, but 
> the source I'm looking at doesn't have a UnixLockFile class, as your log 
> shows. 
>
> Your log shows to calls to _lock_file, but it doesn't show that the both 
> succeed.  Do they? 
>
>
> yes, both succeed. The log I showed was truncated a little bit too early. 
Both threads then worked on the same session file simultaneously, resulting 
in the described behavior that one thread reads incomplete data from the 
session file because the other thread hasn't finished yet writing to it.


As I said I was still working on cherrypy 15. And you are right, in the 
most current cherrypy version zc.lockfile.LockFile() is used. However I run 
into the same problems with cherrypy 18. That is probably due to the fact 
that "The zc.lockfile package provides a basic portable implementation of 
*interprocess* locks using lock files" as its project description states. 


Since in most cases people run cherrypy with multiple threads we might need 
to think about a locking implementation that also supports inter-thread 
locking of a file. Otherwise IMO the locking for file sessions only makes 
half sense.
 

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<div dir=3D"ltr">On Friday, 10 May 2019 19:31:28 UTC+2, Tim Roberts  wrote:=
<blockquote class=3D"gmail_quote" style=3D"margin: 0;margin-left: 0.8ex;bor=
der-left: 1px #ccc solid;padding-left: 1ex;"><br>The zc.lockfile I&#39;m lo=
oking at certainly opens a new fd each time, but=20
<br>the source I&#39;m looking at doesn&#39;t have a UnixLockFile class, as=
 your log=20
<br>shows.
<br>
<br>Your log shows to calls to _lock_file, but it doesn&#39;t show that the=
 both=20
<br>succeed.=C2=A0 Do they?
<br>
<br>
<br></blockquote><div><p>yes, both succeed. The log I showed was truncated =
a little bit
      too early. Both threads then worked on the same session file
      simultaneously, resulting in the described behavior that one
      thread reads incomplete data from the session file because the
      other thread hasn&#39;t finished yet writing to it.</p><p><br>
    </p>
    <p>As I said I was still working on cherrypy 15. And you are right,
      in the most current cherrypy version zc.lockfile.LockFile() is
      used. However I run into the same problems with cherrypy 18. That
      is probably due to the fact that &quot;The zc.lockfile package provid=
es
      a basic portable implementation of
      <b>interprocess</b> locks using lock files&quot; as its project
      description states. <br></p><p><br>
    </p>
    <p>Since in most cases people run cherrypy with multiple threads we
      might need to think about a locking implementation that also
      supports inter-thread locking of a file. Otherwise IMO the locking
      for file sessions only makes half sense.</p>=C2=A0</div></div>

<p></p>

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