jdk.dio.watchdog

Interface WatchdogTimer

All Superinterfaces:

java.lang.AutoCloseable, java.nio.channels.Channel, java.io.Closeable, Device<WatchdogTimer>

All Known Subinterfaces:

WindowedWatchdogTimer

public interface WatchdogTimer
extends Device<WatchdogTimer>

The WatchdogTimer interface provides methods for controlling a watchdog timer that can be used to force the device to reboot (or depending on the platform, the Java Virtual Machine to restart).

A WatchdogTimer instance may represent a virtual watchdog timer. If the device has a single physical watchdog timer, all of the virtual watchdog timers are mapped onto this one physical watchdog timer. It gets set to expire when the virtual watchdog with the earliest timeout is scheduled to expire. The corresponding watchdog timer device is therefore shared and several applications can concurrently acquire the same watchdog timer device.

A watchdog timer may be identified by the numerical ID and by the name (if any defined) that correspond to its registered configuration. A WatchdogTimer instance can be opened by a call to one of the DeviceManager.open(id,...) methods using its ID or by a call to one of the DeviceManager.open(name,...) methods using its name.
If a watchdog timer is virtualized, a particular platform implementation may allow for several WatchdogTimer instances representing each a virtual instance of that same physical watchdog timer to be opened concurrently using the same device ID, or, alternatively, it may assign each virtual watchdog timer instance a distinct device ID (and a common name).

Once the device opened, the application can start using it and can especially start the timer using the WatchdogTimer.start method and subsequently refresh the timer periodically using the WatchdogTimer.refresh method

When done, an application should call the WatchdogTimer.close method to close the watchdog timer. Any further attempt to access or control a watchdog timer which has been closed will result in a ClosedDeviceException been thrown.

Field Summary

Fields inherited from interface jdk.dio.Device

BIG_ENDIAN, LITTLE_ENDIAN, MIXED_ENDIAN

Method Summary

Methods

Modifier and Type	Method and Description
boolean	causedLastReboot() Checks if the last device reboot (or JVM restart) was caused by the watchdog timing out.
long	getMaxTimeout() Gets the maximum timeout that can be set for the watchdog timer.
long	getTimeout() Get the current timeout for the watchdog timer.
void	refresh() Refreshes the watchdog timer.
void	start(long timeout) Starts the watchdog timer with the specified timeout.
void	stop() Stops this watchdog timer.

Methods inherited from interface jdk.dio.Device

close, getDescriptor, isOpen, tryLock, unlock

Method Detail

causedLastReboot

boolean causedLastReboot()
                         throws java.io.IOException,
                                UnavailableDeviceException,
                                ClosedDeviceException

Checks if the last device reboot (or JVM restart) was caused by the watchdog timing out.

Returns:

true if the watchdog timer caused the last device reboot (or JVM restart).

Throws:

java.io.IOException - if some other I/O error occurs.

UnavailableDeviceException - if this device is not currently available - such as it is locked by another application.

ClosedDeviceException - if the device has been closed.

getMaxTimeout

long getMaxTimeout()
                   throws java.io.IOException,
                          UnavailableDeviceException,
                          ClosedDeviceException

Gets the maximum timeout that can be set for the watchdog timer.

Returns:

the maximum time interval (in milliseconds) that can be set for the watchdog timer.

Throws:

java.io.IOException - if some other I/O error occurs.

UnavailableDeviceException - if this device is not currently available - such as it is locked by another application.

ClosedDeviceException - if the device has been closed.

getTimeout

long getTimeout()
                throws java.io.IOException,
                       UnavailableDeviceException,
                       ClosedDeviceException

Get the current timeout for the watchdog timer. A value of zero indicates that the watchdog timer is disabled.

Returns:

the time interval (in milliseconds) until watchdog times out.

Throws:

java.io.IOException - if some other I/O error occurs.

UnavailableDeviceException - if this device is not currently available - such as it is locked by another application.

ClosedDeviceException - if the device has been closed.

refresh

void refresh()
             throws java.io.IOException,
                    UnavailableDeviceException,
                    ClosedDeviceException

Refreshes the watchdog timer. This method must be called periodically to prevent the watchdog from timing out and rebooting the device (or restarting the JVM).

This method has no effect if the timer is currently disabled.

Throws:

java.io.IOException - if some other I/O error occurs.

UnavailableDeviceException - if this device is not currently available - such as it is locked by another application.

ClosedDeviceException - if the device has been closed.

start

void start(long timeout)
           throws java.io.IOException,
                  UnavailableDeviceException,
                  ClosedDeviceException

Starts the watchdog timer with the specified timeout. If the watchdog timer is not refreshed by a call to refresh prior to the watchdog timing out, the device will be rebooted (or the JVM restarted).

Calling this method twice is equivalent to stopping the timer as per a call to stop() and starting it again with the new specified timeout.

Parameters:

timeout - the time interval (in milliseconds) until watchdog times out.

Throws:

java.io.IOException - if some other I/O error occurs.

java.lang.IllegalArgumentException - if timeout is not greater than 0.

UnavailableDeviceException - if this device is not currently available - such as it is locked by another application.

ClosedDeviceException - if the device has been closed.

stop

void stop()
          throws java.io.IOException,
                 UnavailableDeviceException,
                 ClosedDeviceException

Stops this watchdog timer.

This method returns silently if the timer is already disabled.

Throws:

java.io.IOException - if some other I/O error occurs.

UnavailableDeviceException - if this device is not currently available - such as it is locked by another application.

ClosedDeviceException - if the device has been closed.