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<div class="moz-cite-prefix">On 09/29/2012 03:52 PM, Benjamin Wang
(gendwang) wrote:<br>
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<div class="WordSection1">
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:9.6pt"><span
style="color:#1F497D" lang="EN-US">OK. Now I am using JNA to
access libvirt. If we add another mutex which used to access
ˇ°initializedˇ± parameter. This mutex must be
pthread_mutex_init firstly and only once.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">But
it seems that there is no way to change libvirt code. I do
it as following:<o:p></o:p></span></p>
<p class="MsoListParagraph"
style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo1">
<!--[if !supportLists]--><span style="color:#1F497D"
lang="EN-US"><span style="mso-list:Ignore">1.<span
style="font:7.0pt "Times New Roman"">
</span></span></span><!--[endif]--><span
style="color:#1F497D" lang="EN-US">Changing libvirt JNA code
in Connect.java<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Old
Code:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
public Connect(String uri) throws LibvirtException {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
VCP = libvirt.virConnectOpen(uri);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
// Check for an error<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
processError();<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
ErrorHandler.processError(Libvirt.INSTANCE);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">New
Code:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
public Connect(String uri) throws LibvirtException {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
synchronized(this.getClass()) {<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
VCP = libvirt.virConnectOpen(uri);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
// Check for an error<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
processError();<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
ErrorHandler.processError(Libvirt.INSTANCE);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">
}<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">This
can make sure only that one thread can execute Connect. For
a server application, we only need one time. So the
performance is OK<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoListParagraph"
style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0
level1 lfo1">
<!--[if !supportLists]--><span style="color:#1F497D"
lang="EN-US"><span style="mso-list:Ignore">2.<span
style="font:7.0pt "Times New Roman"">
</span></span></span><!--[endif]--><span
style="color:#1F497D" lang="EN-US">Changing libvirt code in
libvirt.c<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Old
Code:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">static
int initialized = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">New
Code:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">static
int volatile initialized = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">This
can make sure the initialization will be executed once.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Would
you give your comments for this solution?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">B.R.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Benjamin
Wang<o:p></o:p></span></p>
<span style="font-size: 12pt; font-family: "Times New
Roman","serif";" lang="EN-US"><br>
</span></div>
</blockquote>
<br>
As far as I know the operations on <code>volatile</code>
variable is not atomic,<br>
the usage of <code>volatile</code> keyword as a portable
synchronization mechanism is discouraged by C.<br>
But in Java, it is a global ordering on the reads and writes to
a volatile variable.<br>
So, maybe, your first solution is pretty enough good.<br>
<br>
Guannan<br>
<br>
<br>
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