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Class FlightRecorder

java.lang.Object

jdk.jfr.FlightRecorder

public final class FlightRecorder extends Object

Class for accessing, controlling, and managing Flight Recorder.

This class provides the methods necessary for creating, starting, stopping, and destroying recordings.

Since:: 9

Method Summary

Modifier and Type	Method	Description
`static void`	`addListener(FlightRecorderListener changeListener)`	Adds a recorder listener and captures the `AccessControlContext` to use when invoking the listener.
`static void`	`addPeriodicEvent(Class<? extends Event> eventClass, Runnable hook)`	Adds a hook for a periodic event.
`List<EventType>`	`getEventTypes()`	Returns an immutable list that contains all currently registered events.
`static FlightRecorder`	`getFlightRecorder()`	Returns the Flight Recorder for the platform.
`List<Recording>`	`getRecordings()`	Returns an immutable list of the available recordings.
`static boolean`	`isAvailable()`	Returns `true` if the Java Virtual Machine (JVM) has Flight Recorder capabilities.
`static boolean`	`isInitialized()`	Returns `true` if Flight Recorder is initialized.
`static void`	`register(Class<? extends Event> eventClass)`	Registers an event class.
`static boolean`	`removeListener(FlightRecorderListener changeListener)`	Removes a recorder listener.
`static boolean`	`removePeriodicEvent(Runnable hook)`	Removes a hook for a periodic event.
`Recording`	`takeSnapshot()`	Creates a snapshot of all available recorded data.
`static void`	`unregister(Class<? extends Event> eventClass)`	Unregisters an event class.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

getRecordings

public List<Recording> getRecordings()

Returns an immutable list of the available recordings.

A recording becomes available when it is created. It becomes unavailable when it is in the CLOSED state, typically after a call to Recording.close().

Returns:: a list of recordings, not null

takeSnapshot

public Recording takeSnapshot()

Creates a snapshot of all available recorded data.

A snapshot is a synthesized recording in a STOPPED state. If no data is available, a recording with size 0 is returned.

A snapshot provides stable access to data for later operations (for example, operations to change the interval or to reduce the data size).

The following example shows how to create a snapshot and write a subset of the data to a file.

try (Recording snapshot = FlightRecorder.getFlightRecorder().takeSnapshot()) {
    if (snapshot.getSize() > 0) {
        snapshot.setMaxSize(100_000_000);
        snapshot.setMaxAge(Duration.ofMinutes(5));
        snapshot.dump(Paths.get("snapshot.jfr"));
    }
}

The caller must close the recording when access to the data is no longer needed.

Returns:: a snapshot of all available recording data, not null

register

public static void register(Class<? extends Event> eventClass)

Registers an event class.

If the event class is already registered, then the invocation of this method is ignored.

Parameters:: eventClass - the event class to register, not null
Throws:: IllegalArgumentException - if class is abstract or not a subclass of Event; SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

unregister

public static void unregister(Class<? extends Event> eventClass)

Unregisters an event class.

If the event class is not registered, then the invocation of this method is ignored.

Parameters:: eventClass - the event class to unregistered, not null
Throws:: IllegalArgumentException - if a class is abstract or not a subclass of Event; SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

getFlightRecorder

public static FlightRecorder getFlightRecorder() throws IllegalStateException, SecurityException

Returns the Flight Recorder for the platform.

Returns:: a Flight Recorder instance, not null
Throws:: IllegalStateException - if Flight Recorder can't be created (for example, if the Java Virtual Machine (JVM) lacks Flight Recorder support, or if the file repository can't be created or accessed); SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

addPeriodicEvent

public static void addPeriodicEvent(Class<? extends Event> eventClass, Runnable hook) throws SecurityException

Adds a hook for a periodic event.

The implementation of the hook should return as soon as possible, to avoid blocking other Flight Recorder operations. The hook should emit one or more events of the specified type. When a hook is added, the interval at which the call is invoked is configurable using the "period" setting.

Parameters:: eventClass - the class that the hook should run for, not null; hook - the hook, not null
Throws:: IllegalArgumentException - if a class is not a subclass of Event, is abstract, or the hook is already added; IllegalStateException - if the event class has the Registered(false) annotation and is not registered manually; SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

removePeriodicEvent

public static boolean removePeriodicEvent(Runnable hook) throws SecurityException

Removes a hook for a periodic event.

Parameters:: hook - the hook to remove, not null
Returns:: true if hook is removed, false otherwise
Throws:: SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("registerEvent")

getEventTypes

public List<EventType> getEventTypes()

Returns an immutable list that contains all currently registered events.

By default, events are registered when they are first used, typically when an event object is allocated. To ensure an event is visible early, registration can be triggered by invoking the register(Class) method.

Returns:: list of events, not null

addListener

public static void addListener(FlightRecorderListener changeListener)

Adds a recorder listener and captures the AccessControlContext to use when invoking the listener.

If Flight Recorder is already initialized when the listener is added, then the method FlightRecorderListener.recorderInitialized(FlightRecorder) method is invoked before returning from this method.

Parameters:: changeListener - the listener to add, not null
Throws:: SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

removeListener

public static boolean removeListener(FlightRecorderListener changeListener)

Removes a recorder listener.

If the same listener is added multiple times, only one instance is removed.

Parameters:: changeListener - listener to remove, not null
Returns:: true, if the listener could be removed, false otherwise
Throws:: SecurityException - if a security manager exists and the caller does not have FlightRecorderPermission("accessFlightRecorder")

isAvailable

public static boolean isAvailable()

Returns true if the Java Virtual Machine (JVM) has Flight Recorder capabilities.

This method can quickly check whether Flight Recorder can be initialized, without actually doing the initialization work. The value may change during runtime and it is not safe to cache it.

Returns:

true, if Flight Recorder is available, false otherwise

See Also:

isInitialized

public static boolean isInitialized()

Returns true if Flight Recorder is initialized.

Returns:

true, if Flight Recorder is initialized, false otherwise

See Also:

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/21/docs/api/jdk.jfr/jdk/jfr/FlightRecorder.html