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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US">I’m developing a C# application that controls VMs, starts them, stops them and runs programs in them. It should also reset the VM to a previously saved snapshot.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">But I get a NullReferenceException because the Console object of my session is null, although I call LockMachine.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Here is the code with which I try to reset the machine after it has been powered down.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">public</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">void</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> Reset(</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">string</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
snapshotName = </span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"BeforeTest"</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> {<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">Logger</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.WriteLine(</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"Resetting
the VM"</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">var</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> writeSession =
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">new</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">SessionClass</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">();<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> m_Machine.LockMachine(writeSession,
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">LockType</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.LockType_Write);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> <o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> </span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">int</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
waitCycles = 0;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">while</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> (writeSession.State
!= </span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">SessionState</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.SessionState_Locked
& waitCycles < 100)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> {<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">Thread</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.Sleep(10);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> waitCycles++;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> }<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">if</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> (writeSession.State
!= </span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">SessionState</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.SessionState_Locked)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">throw</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">new</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">VirtualMachineException</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">(</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"The
VM could not be locked!"</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">var</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> console = writeSession.Console;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">if</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">(console ==
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">null</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">throw</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">new</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">VirtualMachineException</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">(</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"The
Console is null!"</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">);
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#00B050;background:white;mso-highlight:white">//This is where the problem is found</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">var</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> snapshot = m_Machine.FindSnapshot(snapshotName);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">if</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> (snapshot ==
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">null</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">throw</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">new</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">VirtualMachineException</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">(</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"Could
not find Snapshot \""</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> + snapshotName +
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"\""</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">var</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> progress = console.RestoreSnapshot(snapshot);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> progress.WaitForCompletion(30000);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> writeSession.UnlockMachine();<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> waitCycles = 0;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:blue;background:white;mso-highlight:white">while</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> (writeSession.State
!= </span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">SessionState</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.SessionState_Unlocked
& waitCycles < 100)<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> {<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">Thread</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.Sleep(10);<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> waitCycles++;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> }<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"><o:p> </o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#2B91AF;background:white;mso-highlight:white">Logger</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">.WriteLine(</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"
The VM has been reset to the snapshot \""</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white"> + snapshotName +
</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:#A31515;background:white;mso-highlight:white">"\""</span><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">);<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">
</span><span style="font-size:9.5pt;font-family:Consolas;color:black;background:white;mso-highlight:white">}</span><span style="font-size:9.5pt;font-family:Consolas;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.5pt;font-family:Consolas;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I’m using VirtualBox 4.3.12 and the COM API. How can I properly restore a snapshot? Why Is the Console null?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Best Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Daniel<o:p></o:p></span></p>
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