[jboss-as7-dev] Graceful Shutdown (Revision 2)

[Jason T. Greene]

*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.

-- 
- DML
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