org.csstudio.utility.pv

Interface PV

All Known Implementing Classes:

EPICSv3PV

public interface PV

A control system PV.

When 'start'ed, the PV will attempt to connect or do whatever is needed to obtain the meta information like units, precision, ... Then it will subscribe to updates of the current value.

While the PVListener might receive events on a non-UI thread, all the calls to the PV should come from the UI thread to prevent possible deadlocks. (The JNI CA client has deadlocked when both UI and non-UI threads called into it at the 'same' time).

Author:

Kay Kasemir

Method Summary

Modifier and Type	Method and Description
void	addListener(PVListener listener) Add a new listener.
void	blockUntilFirstUpdate(int timeout) The calling thread will be blocked until the first update is received from the PV.
String	getName() Return the name of this PV.
String	getStateInfo() Internal state information on the PV.
IValue	getValue() Get the value.
IValue	getValue(double timeoutSeconds) Synchronous 'get'.
boolean	isConnected() Returns true if this PV is connected or false otherwise.
boolean	isRunning() Returns true if this PV has been started and not yet stopped.
boolean	isWriteAllowed() Returns true if we have write access to the PV or false if we cannot write to the PV.
void	removeListener(PVListener listener) Remove a listener.
void	setValue(Object newValue) Set PV to given value.
void	start() Start the PV: connect, get meta data, subscribe to updates, invoke PVListener for incoming values, ...
void	stop() Stop the PV: disconnect, ...

Method Detail

getValue

IValue getValue(double timeoutSeconds)
         throws PVException

Synchronous 'get'.

Attempts to get a value within the given timeout. Either returns a value within the timeout, or throws an exception at the timeout.

When called for a new channel, i.e. on a channel where neither get nor start have been called, it will also perform the connection attempt, and leave the channel connected after getting a value. To force a disconnect, call stop.

Parameters:

timeoutSeconds - timeout in seconds

Returns:

the value read from the IOC

Throws:

PVException - on error

addListener

void addListener(PVListener listener)

Add a new listener.

Parameters:

listener - the listener to add

removeListener

void removeListener(PVListener listener)

Remove a listener.

Parameters:

listener - the listener to remove

start

void start()
    throws PVException

Start the PV: connect, get meta data, subscribe to updates, invoke PVListener for incoming values, ...

Throws:

PVException - if an error occurs during connection

isRunning

boolean isRunning()

Returns true if this PV has been started and not yet stopped.

Returns:

true if this pv is running or false otherwise.

isConnected

boolean isConnected()

Returns true if this PV is connected or false otherwise.

Returns:

true when connected. While isRunning, we are subscribed for value updates, but we might still be disconnected, at least temporarily.

isWriteAllowed

boolean isWriteAllowed()

Returns true if we have write access to the PV or false if we cannot write to the PV.

Returns:

true if we have write access to the PV

getStateInfo

String getStateInfo()

Internal state information on the PV.

Especially when isConnected() is false, this information might help to diagnose the problem: Did the PV never connect? Was it once connected, but some error occurred?

Returns:

Some human readable state info

stop

void stop()

Stop the PV: disconnect, ... When the PV is no longer needed, one should 'stop' it to release resources.

getValue

IValue getValue()

Get the value.

This is the most recent value. Check isConnected() to see if this is valid, or use inside a PVListener.pvValueUpdate(PV).

Returns:

Returns the most recent value, or null if there is none.

setValue

void setValue(Object newValue)
       throws PVException

Set PV to given value. Should accept Double, Double[], Integer, String, maybe more.

Parameters:

newValue - Value to write to PV

Throws:

PVException - on error

getName

String getName()

Return the name of this PV.

Returns:

the name of the PV

blockUntilFirstUpdate

void blockUntilFirstUpdate(int timeout)
                    throws PVException

The calling thread will be blocked until the first update is received from the PV. If the PV already has a value, the call will return immediately. If no update is received in the given timeout, the method throws an exception.

Parameters:

timeout - the maximum timeout to wait for the update in milliseconds

Throws:

PVException - if no value was received in the specified timeout