Package javax.crac
Successful checkpointing and restoration may require that no checkpointed state exist that might not be validly reproducible when restoring instances from the image. Coordination enables application to proactively discard problematic state ahead of checkpointing, and to reestablish needed state upon restoration. A Java implementation may provide detection of some subsets of state that are known to prevent successful checkpoints.
For example, a state of opened file descriptors or socket may be impossible to store in the image. The implementation may detect such resources and then prevent checkpoint. The application must then close file descriptors and sockets to be successfully checkpointed. Files and sockets may be opened back after restore, then the application is responsible for processing possible exceptions.
Resource
is an interface for receiving checkpoint/restore notifications.
In order to be notified, Resource
needs to be registered in a Context
.
Core
is a core interface for coordination. It provides the global Context
which can be used as default choice.
The global Context
have properties listed below, one can define a custom Context
and register it with the global one.
Core
has also a method to request checkpoint.
Methods of Resource
are invoked as a notification of checkpoint and restore.
If a Resource
is incapable to process notification, corresponding method throws an exception.
The global Context
ensures that exceptions are propagated to a requester of checkpoint/restore.
Context
is a Resource
, that allows other Resource
s to be registered with it.
Context
defines how Resource
s are notified and may provide different guarantees compared to the global Context
, such as order of notification.
A class may extend Context
and define custom rules of notification processing by overriding Resource
method.
Since a Context
may be registered with other Context
, they form a Context
hierarchy.
Checkpoint can requested by Core.checkpointRestore
or by some other way.
Then checkpoint notification of the global Context
is performed.
If the global Context
have not thrown CheckpointException
, the current Java instance is used to create the image in a platform dependent way.
The current instance is terminated.
Later, a new instance is created by some means, for example via Java launcher in a special mode.
The new instance is started at the point where the image was created, it is followed by the restore notification.
Exceptions from restore notification are provided as suppressed ones by a RestoreException
(in a sense of Throwable.addSuppressed(java.lang.Throwable)
).
If the global Context
throws an exception during checkpoint notification then restore notificaion starts immediately without the image creation.
In this case, exceptions from checkpoint and restore notifications are provided as suppressed ones by CheckpointException
.
UnsupportedOperationException
is thrown if the service is not supported.
No notification is performed in this case.
Global Context Properties
Java Runtime maintains the globalContext
with following properties.
An implementor is encouraged to define Context
with the properties of the global Context
.
- The
Context
maintains a weak reference to registeredResource
. - Order of checkpoint notification is the reverse order of registration. Restore notification order is the reverse of checkpoint one, that is, forward order of registration.
- For single
Resource
registered in thisContext
:Resource
is always notified of checkpoint, regardless of otherResource
notifications have thrown an exception or not,Resource
is always notified of restore, regardless of its checkpoint or others' restore notification have thrown an exception or not.- When an exception is thrown during notificaion, it is caught by the
Context
and is suppressed by aCheckpointException
orRestoreException
, depends on the throwing method. - When the
Resource
is aContext
and it throwsCheckpointException
orRestoreException
, exceptions suppressed by the original exception are suppressed by anotherCheckpointException
orRestoreException
, depends on the throwing method.
- All exceptions thrown by
Resource
are suppressed byCheckpointException
orRestoreException
thrown by theContext
.
- Since:
- TBD
-
ClassDescriptionThis exception works as an aggregate for all errors found during checkpoint; these are recorded as suppressed exceptions.A
Resource
that allows otherResource
s to be registered with it.The coordination service.An interface for receiving checkpoint/restore notifications.This exception works as an aggregate for all errors found during checkpoint; these are recorded as suppressed exceptions.