Deadlocks may be caused by Declarative Services
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Key: FELIX-490
URL: https://issues.apache.org/jira/browse/FELIX-490
Project: Felix
Issue Type: Bug
Components: Declarative Services
Affects Versions: 1.0.0
Reporter: Felix Meschberger
The Declarative Services implementation has an AbstractComponentManager class
which implementa the lifecycles of components in methods like enable, activate,
deactivate, disable and dispose. All methods come in two flavors an (private)
internal on which is synchronized and executes the action and a public
unsynchronized one calling the internal one on a separate thread.
All internal methods are generally called only from the separate thread so are
guaranteed to run sequentially on after the other due to the queing in the
thread. One exception is the deactivate method which is always called directly
and not in the separate thread. So a component may be deactivated while it is
actually being activated. This is why the internal methods are synchronized -
to delay a deactivation in case an activation already active.
The problem is, that activate calls in to the framework to get at services or
to register services. At the same time the deactivate method may be called from
within the framework for example because a required or static dependency has
been unregistered. This may now create a deadlock between the activate method
trying to register a service and the service unregistration trying to call the
deactivate method.
The fix is to look at a more finegrained synchronization mechanism in the
AbstractComponentManager.
Similar behaviour is reported in FELIX-489, which is currently analysed looking
from the framework to the outside.
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