[libvirt-users] is libvirt java binding thread safe?

[Matthias Bolte]

2010/9/3 Daniel P. Berrange <berrange at redhat.com>:
> On Fri, Sep 03, 2010 at 01:02:09PM +0200, Matthias Bolte wrote:
>> Ah, okay, now I understand what you want to say.
>>
>> You have two threads A and B. When A runs on its own then it's just
>> fine, but when you add B (that triggers an exception on purpose and
>> ignores it) then A picks it up and reports it. This is the point where
>> thread safety comes to mind.
>>
>> libvirt stores errors in thread-local-storage. It uses
>> pthread_key_create/pthread_{get,set}specific for this (or
>> TlsAlloc/Tls{Get,Set}Value on Windows).
>>
>> I think what's happening here is that all your threads in Java share
>> the same thread-local-storage. Therefore, thread A can pickup the
>> error triggered by thread B, that should not happen.
>>
>> I'm not sure how to fix that.
>
> Looking at the java code, I believe the problem is that the java
> bindings are *not* using the threadsafe error APIs:
>
> In Connect.java
>
>    /**
>     * call the error handling logic. Should be called after every libvirt call
>     *
>     * @throws LibvirtException
>     */
>    protected void processError() throws LibvirtException {
>        ErrorHandler.processError(libvirt, VCP);
>    }
>
> Which calls into
>
>    public static void processError(Libvirt libvirt, ConnectionPointer conn) throws LibvirtException {
>        virError vError = new virError();
>        int errorCode = libvirt.virConnCopyLastError(conn, vError);
>
> And virConnCopyLastError is *not* threadsafe:
>
>
> /**
>  * virConnCopyLastError:
>  * @conn: pointer to the hypervisor connection
>  * @to: target to receive the copy
>  *
>  * Copy the content of the last error caught on that connection
>  *
>  * This method is not protected against access from multiple
>  * threads. In a multi-threaded application, always use the
>  * global virGetLastError() API which is backed by thread
>  * local storage.
>
> Regards,
> Daniel

Hm that might explain it, I'll check if that's the cause.

Matthias