Tom Watson created FELIX-6616:
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Summary: Dynamic greedy 1..1 references may activate with no
reference service bound
Key: FELIX-6616
URL: https://issues.apache.org/jira/browse/FELIX-6616
Project: Felix
Issue Type: Bug
Components: Declarative Services (SCR)
Affects Versions: scr-2.2.6
Reporter: Tom Watson
Assignee: Tom Watson
Fix For: scr-2.2.8
If using a 1..1 cardinality for a dynamic greedy reference there is a timing
issue possible which will cause SCR to unbind all reference when activating the
component.
The timing window involves at least two threads.
1) thread 1 is in the process of activating the component with a 1..1 dynamic
greedy reference to service X (ranking=1)
2) thread 2 is in the process of registering another service X with a higher
service ranking=100
When this happens thread 1 determines it should bind service X ranking 1.
Thread 1 creates the service component instance and enables the tracking of all
the dependencies. It then proceeds to bind all the required services. Before
binding service X ranking=1 thread 2 registers service X ranking=100. Thread 2
then finds the created service component instance that thread 1 has created
(but is still in the process of binding all the services) and then thread 2
binds service X ranking=100. At this point thread 2 thinks the component
actually got bound to service X ranking=1 so it begins to unbind it. Before
unbinding, if thread 1 proceeds it will bind service X ranking=1. So now the
component itself (depending on the implementation) will start using X
ranking=1. But then thread 2 proceeds and it will unbind service X ranking=1.
So basically we are left with this flow:
1) bind X ranking=100
2) bind X ranking=1
3) unbind X ranking =1
At this point the component will be confused and think it likely has no
services to use.
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