Possible synchronization issue with BundleContext.getBundle()
-------------------------------------------------------------
Key: FELIX-2748
URL: https://issues.apache.org/jira/browse/FELIX-2748
Project: Felix
Issue Type: Bug
Components: Framework
Affects Versions: framework-3.0.6
Reporter: Sahoo
On 12/26/10 23:24, Sahoo wrote:
> Hi,
>
> Looking at the code, it seems to me that BundleContext.getBundle() can return
> a bundle even though the BundleContext has been invalidated. I say this based
> on the following reasoning:
>
> public BundleContext.getBundle()
> {
> checkValidity();
>
> return m_bundle;
> }
>
> private void checkValidity() // non-synchronized method
> {
> if (m_valid) // m_valid is a non-volatile field
> {
> switch (m_bundle.getState())
> {
> case Bundle.ACTIVE:
> case Bundle.STARTING:
> case Bundle.STOPPING:
> return;
> }
> }
>
> throw new IllegalStateException("Invalid BundleContext.");
>
> }
>
> protected void invalidate() { m_valid = false; }
>
> class Bundle {
> public int getState() // non-synchronized method
> {
> return m_state;
> }
> }
>
> time t1: thread1 has access to bundleContext.
> time t2: thread2 calls b.update()
> time t3: bundle has been stopped and is now in STARTING state. thread1 calls
> bundleContext.getBundle().
> Since m_valid is not a volatile field, it can see m_valid as true, although
> thread2 would have set it to false. Since m_state is volatile, it sees its
> value as STARTING. So, it fails to detect invalidation of the bundle and is
> returned with the bundle object instead of IllegalStateException.
>
> Am I missing anything here?
No, I think you are correct.
I'll have to think about it a little more, but I think the real issue here is
the fact that the validity of the bundle context has to be more directly tied
to the bundle. They can't be treated as independent values, because even if
they were both volatile or synchronized, you could still end up with a change
in state between checking each value.
I think the simpler BundleContext.checkValidity() method should be something
like:
m_bundle._getBundleContext() == this
Which says as long as "this" bundle context is the bundle's bundle context,
then it is valid. I think. I'll still need to think about it. :-)
Want to open a bug on this issue?
Is this a theoretical exercise or are you suffering from this?
-> richard
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