Re: [jboss-as7-dev] Graceful Shutdown (Revision 2)
Are you sure explicity granting "permits" through a "Shutdown Manager"
the way to go? Having to interact with a central service that grants
permits per-request is very worrisome. The subsystem may already have a
better way to do graceful shutdown, or just cannot follow a permit pattern.
Is it not simpler and gives more flexibility to a subsystem to drive
this via events rather than explicit callbacks to a Shutdown Manager?
i.e.
class Suspending extends ShutdownEvent
{
void iFinishedSuspending(); // the callback to the Shutdown Manager
}
GIves the subsystem flexibility on how best to implement a graceful
shutdown.
On 6/26/12 11:00 AM, Jason T. Greene wrote:
*EDITED*
We've worked out the rough outline of how graceful shutdown will work in
AS7.
The process of graceful shutdown actually is reflected by a number of
states:
1. Running - all services acting normally
2. Suspending - services refuse new "permits" (see below), existing
permits are allowed to be retained (and threads running under such a
permit may still acquire new permits)
3. Suspended - no permits are present and none may be issued
4. Shutting Down - our existing server stop process / reload admin mode
The following transitions are allowed:
1. Running → Suspending: Transition occurs at user request (to suspend
or gracefully shut down).
2. Suspending → Suspended: Transition occurs when all permits are cleared.
3. Suspending → Running: Transition occurs at user request (to exit
suspend mode or cancel graceful shutdown before it completes).
4. Suspended → Running: Transition occurs at user request (to exit
suspend mode).
5. Suspended → Shutting Down: Transition occurs automatically (if a
graceful shutdown was requested) or at user request (if a shut down
request of any kind is entered in the Suspended state).
6. Running → Shutting Down: Transition occurs at user request (to shut
down the server "un-gracefully").
7. Suspending → Shutting Down (User aborts a graceful shutdown)
These "permits" are issued by the "Shutdown Manager", whose job is
to
manage these states. They are issued corresponding to the following events:
1. The invocation of an EJB method
2. The creation of a web session
3. A creation of a transaction
4. MessageEndpoint and WorkManager aquire permit allowing for release()
from a thirdparty to indicate connection close.
When a permit cannot be issued due to the server shutting down, a
standard exception message should be produced so that the user can see a
familiar error message regardless of what mechanism is used to access
the server.
--
Bill Burke
JBoss, a division of Red Hat
http://bill.burkecentral.com