public static class Operator.OperatorStates extends Object
The state of a given Operator may also be changed independently of its
application through sbadmin.
Informally, an Operator transitions through states as follows. The
initial state of an Operator is NOT_YET_STARTED. In this
state an Operator has been instantiated and its init()
method has been called.
From NOT_YET_STARTED an Operator transitions to the
STARTED state. An Operator starts either because its
containing application has started or because it has been started through
sbadmin. An Operator receives two callbacks from the
StreamBase runtime when it starts, resume() and
resumed(). First, the runtime calls the
resume() method. Once resume() has returned,
any threads that the Operator has registered are started, if need be.
Next, the Operator transitions to the STARTED state. The
Operator then receives a second callback, resumed().
From the STARTED state, the Operator may transition to the
SUSPENDED state. An Operator may transition to
SUSPENDED because its application has suspended or because
it has been explicitly suspended with sbadmin. The
StreamBase runtime also makes call backs on suspend; first the
suspend() callback is made, then the Operator transitions to
the SUSPENDED state, then the suspended()
callback is made.
From SUSPENDED, an Operator can transition back to
STARTED. This is referred to as 'resuming'. An Operator can
resume when its application resumes or when it is explicitly resumed
through sbadmin.
An Operator get the same callbacks from the runtime when it starts and
when it resumes, resume() and resumed().
Essentially then, these two transitions, starting and resuming, are
equivalent. This implies then that any code that should be run just once
for an instance of an Operator belongs in its init() method,
rather than in the resume() or resumed()
methods.
An Operator can transition between STARTED and
SUSPENDED any number of times.
SHUTDOWN is an Operator's terminal state. An Operator can
enter the SHUTDOWN state from any of its other states. The
StreamBase runtime calls back to the method shutdown prior
to entering SHUTDOWN.
An instance of an Operator can not be recovered from a state of
SHUTDOWN. Once shut down, an Operator can be 'restarted'
using the sbadmin restart command. However, this causes a
new Operator instance to be constructed and its init()
method to be called. Any state held by the prior instance of the Operator
is lost.
| Modifier and Type | Field and Description |
|---|---|
static int |
NONE |
static int |
NOT_YET_STARTED
The initial state of an Operator.
|
static int |
SHUTDOWN
The terminal state of the Operator.
|
static int |
STARTED
The Operator has been started; resume() has been called.
|
static int |
SUSPENDED
The Operator has been suspended; suspend() has been called.
|
public static final int NONE
public static final int NOT_YET_STARTED
public static final int STARTED
public static final int SUSPENDED
public static final int SHUTDOWN