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/OpenJDK 21

Class Recording

java.lang.Object
jdk.jfr.Recording
All Implemented Interfaces:
Closeable, AutoCloseable 
public final class Recording extends Object implements Closeable
Provides means to configure, start, stop and dump recording data to disk.

The following example shows how configure, start, stop and dump recording data to disk. 

Configuration c = Configuration.getConfiguration("default");
try (Recording r = new Recording(c)) {
    r.start();
    System.gc();
    Thread.sleep(5000);
    r.stop();
    r.dump(Files.createTempFile("my-recording", ".jfr"));
}
Since:
9

Constructor Summary

Constructor Description
Recording()
Creates a recording without any settings.
Recording(Map<String,String> settings)
Creates a recording with settings from a map of name-value pairs.
Recording(Configuration configuration)
Creates a recording with settings from a configuration.

Method Summary

Modifier and Type Method Description
void close()
Releases all data that is associated with this recording.
Recording copy(boolean stop)
Returns a clone of this recording, with a new recording ID and name.
EventSettings disable(Class<? extends Event> eventClass)
Disables event.
EventSettings disable(String name)
Disables event with the specified name.
void dump(Path destination)
Writes recording data to a file.
EventSettings enable(Class<? extends Event> eventClass)
Enables event.
EventSettings enable(String name)
Enables the event with the specified name.
Path getDestination()
Returns the destination file, where recording data is written when the recording stops, or null if no destination is set.
boolean getDumpOnExit()
Returns whether this recording is dumped to disk when the JVM exits.
Duration getDuration()
Returns the specified duration for this recording, or null if no duration is set.
long getId()
Returns a unique ID for this recording.
Duration getMaxAge()
Returns the length of time that the data is kept in the disk repository before it is removed.
long getMaxSize()
Returns the maximum size, measured in bytes, at which data is no longer kept in the disk repository.
String getName()
Returns the name of this recording.
Map<String,String> getSettings()
Returns settings used by this recording.
long getSize()
Returns the current size of this recording in the disk repository, measured in bytes.
Instant getStartTime()
Returns the time when this recording was started.
RecordingState getState()
Returns the recording state that this recording is currently in.
Instant getStopTime()
Returns the time when this recording was stopped.
InputStream getStream(Instant start, Instant end)
Creates a data stream for a specified interval.
boolean isToDisk()
Returns true if this recording uses the disk repository, false otherwise.
void scheduleStart(Duration delay)
Starts this recording after a delay.
void setDestination(Path destination)
Sets a location where data is written on recording stop, or null if data is not to be dumped.
void setDumpOnExit(boolean dumpOnExit)
Sets whether this recording is dumped to disk when the JVM exits.
void setDuration(Duration duration)
Sets a duration for how long a recording runs before it stops.
void setMaxAge(Duration maxAge)
Determines how far back data is kept in the disk repository.
void setMaxSize(long maxSize)
Determines how much data is kept in the disk repository.
void setName(String name)
Sets a human-readable name (for example, "My Recording").
void setSettings(Map<String,String> settings)
Replaces all settings for this recording.
void setToDisk(boolean disk)
Determines whether this recording is continuously flushed to the disk repository or data is constrained to what is available in memory buffers.
void start()
Starts this recording.
boolean stop()
Stops this recording.

Methods declared in class java.lang.Object

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

Constructor Details

Recording

public Recording(Map<String,String> settings)
Creates a recording with settings from a map of name-value pairs.

A newly created recording is in the RecordingState.NEW state. To start the recording, invoke the start() method.

Parameters:
settings - settings as a map of name-value pairs, 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 is used and FlightRecorderPermission "accessFlightRecorder" is not set.
See Also:

Recording

public Recording()
Creates a recording without any settings.

A newly created recording is in the RecordingState.NEW state. To start the recording, invoke the start() method.

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 is used and FlightRecorderPermission "accessFlightRecorder" is not set.

Recording

public Recording(Configuration configuration)
Creates a recording with settings from a configuration.

The following example shows how create a recording that uses a predefined configuration. 

Recording r = new Recording(Configuration.getConfiguration("default"));
The newly created recording is in the RecordingState.NEW state. To start the recording, invoke the start() method.
Parameters:
configuration - configuration that contains the settings to be use, 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 is used and FlightRecorderPermission "accessFlightRecorder" is not set.
See Also:

Method Details

start

public void start()
Starts this recording.

It's recommended that the recording options and event settings are configured before calling this method. The benefits of doing so are a more consistent state when analyzing the recorded data, and improved performance because the configuration can be applied atomically.

After a successful invocation of this method, this recording is in the RUNNING state.

Throws:
IllegalStateException - if recording is already started or is in the CLOSED state

scheduleStart

public void scheduleStart(Duration delay)
Starts this recording after a delay.

After a successful invocation of this method, this recording is in the DELAYED state.

Parameters:
delay - the time to wait before starting this recording, not null
Throws:
IllegalStateException - if the recording is not it the NEW state

stop

public boolean stop()
Stops this recording.

When a recording is stopped it can't be restarted. If this recording has a destination, data is written to that destination and the recording is closed. After a recording is closed, the data is no longer available.

After a successful invocation of this method, this recording will be in the STOPPED state.

Returns:
true if recording is stopped, false otherwise
Throws:
IllegalStateException - if the recording is not started or is already stopped
SecurityException - if a security manager exists and the caller doesn't have FilePermission to write to the destination path
See Also:

getSettings

public Map<String,String> getSettings()
Returns settings used by this recording.

Modifying the returned Map will not change the settings for this recording.

If no settings are set for this recording, an empty Map is returned.

Returns:
recording settings, not null

getSize

public long getSize()
Returns the current size of this recording in the disk repository, measured in bytes.

The size is updated when recording buffers are flushed. If the recording is not written to the disk repository the returned size is always 0.

Returns:
amount of recorded data, measured in bytes, or 0 if the recording is not written to the disk repository

getStopTime

public Instant getStopTime()
Returns the time when this recording was stopped.
Returns:
the time, or null if this recording is not stopped

getStartTime

public Instant getStartTime()
Returns the time when this recording was started.
Returns:
the time, or null if this recording is not started

getMaxSize

public long getMaxSize()
Returns the maximum size, measured in bytes, at which data is no longer kept in the disk repository.
Returns:
maximum size in bytes, or 0 if no maximum size is set

getMaxAge

public Duration getMaxAge()
Returns the length of time that the data is kept in the disk repository before it is removed.
Returns:
maximum length of time, or null if no maximum length of time has been set

getName

public String getName()
Returns the name of this recording.

By default, the name is the same as the recording ID.

Returns:
the recording name, not null

setSettings

public void setSettings(Map<String,String> settings)
Replaces all settings for this recording.

The following example shows how to set event settings for a recording. 

    Map<String, String> settings = new HashMap<>();
    settings.putAll(EventSettings.enabled("jdk.CPUSample").withPeriod(Duration.ofSeconds(2)).toMap());
    settings.putAll(EventSettings.enabled(MyEvent.class).withThreshold(Duration.ofSeconds(2)).withoutStackTrace().toMap());
    settings.put("jdk.ExecutionSample#period", "10 ms");
    recording.setSettings(settings);
The following example shows how to merge settings. 
    Map<String, String> settings = recording.getSettings();
    settings.putAll(additionalSettings);
    recording.setSettings(settings);
Parameters:
settings - the settings to set, not null

getState

public RecordingState getState()
Returns the recording state that this recording is currently in.
Returns:
the recording state, not null
See Also:

close

public void close()
Releases all data that is associated with this recording.

After a successful invocation of this method, this recording is in the CLOSED state.

Specified by:
close in interface AutoCloseable
Specified by:
close in interface Closeable

copy

public Recording copy(boolean stop)
Returns a clone of this recording, with a new recording ID and name.

Clones are useful for dumping data without stopping the recording. After a clone is created, the amount of data to copy is constrained with the setMaxAge(Duration) method and the setMaxSize(long)method.

Parameters:
stop - true if the newly created copy should be stopped immediately, false otherwise
Returns:
the recording copy, not null

dump

public void dump(Path destination) throws IOException
Writes recording data to a file.

For a dump to succeed, the recording must either be 1) running, or 2) stopped and to disk. If the recording is in any other state, an IOException is thrown.

Parameters:
destination - the location where recording data is written, not null
Throws:
IOException - if recording data can't be copied to the specified location, for example, if the recording is closed or the destination path is not writable
SecurityException - if a security manager exists and the caller doesn't have FilePermission to write to the destination path
See Also:

isToDisk

public boolean isToDisk()
Returns true if this recording uses the disk repository, false otherwise.

If no value is set, true is returned.

Returns:
true if the recording uses the disk repository, false otherwise

setMaxSize

public void setMaxSize(long maxSize)
Determines how much data is kept in the disk repository.

To control the amount of recording data that is stored on disk, the maximum amount of data to retain can be specified. When the maximum limit is exceeded, the Java Virtual Machine (JVM) removes the oldest chunk to make room for a more recent chunk.

If neither maximum limit or the maximum age is set, the size of the recording may grow indefinitely.

Parameters:
maxSize - the amount of data to retain, 0 if infinite
Throws:
IllegalArgumentException - if maxSize is negative
IllegalStateException - if the recording is in CLOSED state

setMaxAge

public void setMaxAge(Duration maxAge)
Determines how far back data is kept in the disk repository.

To control the amount of recording data stored on disk, the maximum length of time to retain the data can be specified. Data stored on disk that is older than the specified length of time is removed by the Java Virtual Machine (JVM).

If neither maximum limit or the maximum age is set, the size of the recording may grow indefinitely.

Parameters:
maxAge - the length of time that data is kept, or null if infinite
Throws:
IllegalArgumentException - if maxAge is negative
IllegalStateException - if the recording is in the CLOSED state

setDestination

public void setDestination(Path destination) throws IOException
Sets a location where data is written on recording stop, or null if data is not to be dumped.

If a destination is set, this recording is automatically closed after data is successfully copied to the destination path.

If a destination is not set, Flight Recorder retains the recording data until this recording is closed. Use the dump(Path) method to manually write data to a file.

Parameters:
destination - the destination path, or null if recording should not be dumped at stop
Throws:
IllegalStateException - if recording is in the STOPPED or CLOSED state.
SecurityException - if a security manager exists and the caller doesn't have FilePermission to read, write, and delete the destination file
IOException - if the path is not writable

getDestination

public Path getDestination()
Returns the destination file, where recording data is written when the recording stops, or null if no destination is set.
Returns:
the destination file, or null if not set.

getId

public long getId()
Returns a unique ID for this recording.
Returns:
the recording ID

setName

public void setName(String name)
Sets a human-readable name (for example, "My Recording").
Parameters:
name - the recording name, not null
Throws:
IllegalStateException - if the recording is in CLOSED state

setDumpOnExit

public void setDumpOnExit(boolean dumpOnExit)
Sets whether this recording is dumped to disk when the JVM exits.
Parameters:
dumpOnExit - if this recording should be dumped when the JVM exits

getDumpOnExit

public boolean getDumpOnExit()
Returns whether this recording is dumped to disk when the JVM exits.

If dump on exit is not set, false is returned.

Returns:
true if the recording is dumped on exit, false otherwise.

setToDisk

public void setToDisk(boolean disk)
Determines whether this recording is continuously flushed to the disk repository or data is constrained to what is available in memory buffers.
Parameters:
disk - true if this recording is written to disk, false if in-memory

getStream

public InputStream getStream(Instant start, Instant end) throws IOException
Creates a data stream for a specified interval.

The stream may contain some data outside the specified range.

If the recording is not to disk, a stream can't be created and null is returned.

Parameters:
start - the start time for the stream, or null to get data from start time of the recording
end - the end time for the stream, or null to get data until the present time.
Returns:
an input stream, or null if no data is available in the interval, or the recording was not recorded to disk
Throws:
IllegalArgumentException - if end happens before start
IOException - if a stream can't be opened
See Also:

getDuration

public Duration getDuration()
Returns the specified duration for this recording, or null if no duration is set.

The duration can be set only when the recording is in the RecordingState.NEW state.

Returns:
the desired duration of the recording, or null if no duration has been set.

setDuration

public void setDuration(Duration duration)
Sets a duration for how long a recording runs before it stops.

By default, a recording has no duration (null).

Parameters:
duration - the duration, or null if no duration is set
Throws:
IllegalStateException - if recording is in the STOPPED or CLOSED state

enable

public EventSettings enable(String name)
Enables the event with the specified name.

If multiple events have the same name (for example, the same class is loaded in different class loaders), then all events that match the name are enabled. To enable a specific class, use the enable(Class) method or a String representation of the event type ID.

Parameters:
name - the settings for the event, not null
Returns:
an event setting for further configuration, not null
See Also:

disable

public EventSettings disable(String name)
Disables event with the specified name.

If multiple events with same name (for example, the same class is loaded in different class loaders), then all events that match the name is disabled. To disable a specific class, use the disable(Class) method or a String representation of the event type ID.

Parameters:
name - the settings for the event, not null
Returns:
an event setting for further configuration, not null

enable

public EventSettings enable(Class<? extends Event> eventClass)
Enables event.
Parameters:
eventClass - the event to enable, not null
Returns:
an event setting for further configuration, not null
Throws:
IllegalArgumentException - if eventClass is an abstract class or not a subclass of Event

disable

public EventSettings disable(Class<? extends Event> eventClass)
Disables event.
Parameters:
eventClass - the event to enable, not null
Returns:
an event setting for further configuration, not null
Throws:
IllegalArgumentException - if eventClass is an abstract class or not a subclass of Event

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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/Recording.html