OpenJDK 27 · jdk.internal.perf.Perf · APIdia, the JavaDoc alternative

Modifier and Type	Class and Description
private static class	Perf.CleanerAction

Modifier and Type	Field and Description
private static Perf	instance

Access	Constructor and Description
private	Perf()

Method Summary

Modifier and Type	Method and Description
public ByteBuffer	Returns: ByteBuffer a direct allocated byte buffer attach(int an integer that uniquely identifies the target local Java virtual machine. lvmid) Attach to the instrumentation buffer for the specified Java virtual machine.
private native ByteBuffer	Returns: ByteBuffer a direct allocated byte buffer attach0(int an integer that uniquely identifies the target local Java virtual machine. lvmid) Native method to perform the implementation specific attach mechanism.
public native ByteBuffer	Returns: ByteBuffer a direct allocated byte buffer that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units createByteArray(String the name of this entry. name, int the variability characteristic for this entry. variability, int the units for this entry. units, byte[] the initial value for this entry. value, int the maximum length of this byte array. maxLength) Create a `byte` vector entry in the instrumentation buffer with the given variability characteristic, units, and initial value.
public native ByteBuffer	Returns: ByteBuffer a direct allocated ByteBuffer object that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units createLong(String the name of this entry. name, int the variability characteristic for this entry. variability, int the units for this entry. units, long the initial value for this entry. value) Create a `long` scalar entry in the instrumentation buffer with the given variability characteristic, units, and initial value.
public ByteBuffer	Returns: ByteBuffer a direct allocated ByteBuffer that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units createString(String the name of this entry. name, int the variability characteristic for this entry. variability, int the units for this entry. units, String the initial value for this entry. value, int the maximum string length for this string instrument. maxLength) Create a `String` entry in the instrumentation buffer with the given variability characteristic, units, and initial value.
public ByteBuffer	Returns: ByteBuffer a direct allocated ByteBuffer that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units createString(String the name of this entry. name, int the variability characteristic for this entry. variability, int the units for this entry. units, String the initial value for this entry. value) Create a `String` entry in the instrumentation buffer with the given variability characteristic, units, and initial value.
private native void	detach(ByteBuffer A direct allocated byte buffer created by the `attach` method. bb) Native method to perform the implementation specific detach mechanism.
public static Perf	Returns: A reference to the singleton Perf instance. getPerf() Return a reference to the singleton Perf instance.
public native long	Returns: the number of ticks of machine dependent resolution since the start of the Java virtual machine. highResCounter() Return the value of the High Resolution Counter.
public native long	Returns: the frequency of the High Resolution Counter. highResFrequency() Returns the frequency of the High Resolution Counter, in ticks per second.
private static native void	registerNatives()

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

instance	back to summary
private static Perf instance

Perf	back to summary
private Perf()

Method Detail

attach back to summary

attach	back to summary
public ByteBuffer attach(int lvmid) throws IOException Attach to the instrumentation buffer for the specified Java virtual machine. This method will attach to the instrumentation buffer for the specified virtual machine. It returns a `ByteBuffer` object that is initialized to access the instrumentation buffer for the indicated Java virtual machine. The `lvmid` parameter is a integer value that uniquely identifies the target local Java virtual machine. It is typically, but not necessarily, the process id of the target Java virtual machine. If the `lvmid` identifies a Java virtual machine different from the one running this method, then the coherency characteristics of the buffer are implementation dependent. Implementations that do not support named, coherent, shared memory may return a `ByteBuffer` object that contains only a snap shot of the data in the instrumentation buffer. Implementations that support named, coherent, shared memory, may return a `ByteBuffer` object that will be changing dynamically over time as the target Java virtual machine updates its mapping of this buffer. If the `lvmid` is 0 or equal to the actual `lvmid` for the Java virtual machine running this method, then the returned `ByteBuffer` object will always be coherent and dynamically changing. Parameters lvmid:int an integer that uniquely identifies the target local Java virtual machine. Returns:ByteBuffer ByteBuffer a direct allocated byte buffer Exceptions IOException: An I/O error occurred while trying to acquire the instrumentation buffer. IllegalArgumentException: The lvmid was invalid. OutOfMemoryError: The instrumentation buffer could not be mapped into the virtual machine's address space. See Also `java.nio.ByteBuffer`

public ByteBuffer attach(int lvmid) throws IOException

Attach to the instrumentation buffer for the specified Java virtual machine.

This method will attach to the instrumentation buffer for the specified virtual machine. It returns a ByteBuffer object that is initialized to access the instrumentation buffer for the indicated Java virtual machine. The lvmid parameter is a integer value that uniquely identifies the target local Java virtual machine. It is typically, but not necessarily, the process id of the target Java virtual machine.

If the lvmid identifies a Java virtual machine different from the one running this method, then the coherency characteristics of the buffer are implementation dependent. Implementations that do not support named, coherent, shared memory may return a ByteBuffer object that contains only a snap shot of the data in the instrumentation buffer. Implementations that support named, coherent, shared memory, may return a ByteBuffer object that will be changing dynamically over time as the target Java virtual machine updates its mapping of this buffer.

If the lvmid is 0 or equal to the actual lvmid for the Java virtual machine running this method, then the returned ByteBuffer object will always be coherent and dynamically changing.

Parameters

lvmid:int: an integer that uniquely identifies the target local Java virtual machine.

Returns:ByteBuffer

ByteBuffer a direct allocated byte buffer

Exceptions

IOException:: An I/O error occurred while trying to acquire the instrumentation buffer.
IllegalArgumentException:: The lvmid was invalid.
OutOfMemoryError:: The instrumentation buffer could not be mapped into the virtual machine's address space.

See Also

java.nio.ByteBuffer

attach0 back to summary

attach0	back to summary
private native ByteBuffer attach0(int lvmid) throws IOException Native method to perform the implementation specific attach mechanism. The implementation of this method may return distinct or identical `ByteBuffer` objects for two distinct calls requesting attachment to the same Java virtual machine. For the Sun HotSpot JVM, two distinct calls to attach to the same target Java virtual machine will result in two distinct ByteBuffer objects returned by this method. This may change in a future release. Parameters lvmid:int an integer that uniquely identifies the target local Java virtual machine. Returns:ByteBuffer ByteBuffer a direct allocated byte buffer Exceptions IOException: An I/O error occurred while trying to acquire the instrumentation buffer. IllegalArgumentException: The lvmid was invalid. OutOfMemoryError: The instrumentation buffer could not be mapped into the virtual machine's address space.

private native ByteBuffer attach0(int lvmid) throws IOException

Native method to perform the implementation specific attach mechanism.

The implementation of this method may return distinct or identical ByteBuffer objects for two distinct calls requesting attachment to the same Java virtual machine.

For the Sun HotSpot JVM, two distinct calls to attach to the same target Java virtual machine will result in two distinct ByteBuffer objects returned by this method. This may change in a future release.

Parameters

lvmid:int: an integer that uniquely identifies the target local Java virtual machine.

Returns:ByteBuffer

ByteBuffer a direct allocated byte buffer

Exceptions

IOException:: An I/O error occurred while trying to acquire the instrumentation buffer.
IllegalArgumentException:: The lvmid was invalid.
OutOfMemoryError:: The instrumentation buffer could not be mapped into the virtual machine's address space.

createByteArray back to summary

createByteArray	back to summary
public native ByteBuffer createByteArray(String name, int variability, int units, byte[] value, int maxLength) Create a `byte` vector entry in the instrumentation buffer with the given variability characteristic, units, and initial value. The `maxLength` parameter limits the size of the byte array instrument such that the initial or subsequent updates beyond this length are silently ignored. No special handling of truncated updates is provided. The underlying implementation may further limit the length of the length of the initial or subsequent value. Access to the instrument is provided through the returned `ByteBuffer` object. Parameters name:String the name of this entry. variability:int the variability characteristic for this entry. units:int the units for this entry. value:byte[] the initial value for this entry. maxLength:int the maximum length of this byte array. Returns:ByteBuffer ByteBuffer a direct allocated byte buffer that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units See Also `java.nio.ByteBuffer`

public native ByteBuffer createByteArray(String name, int variability, int units, byte[] value, int maxLength)

Create a byte vector entry in the instrumentation buffer with the given variability characteristic, units, and initial value.

The maxLength parameter limits the size of the byte array instrument such that the initial or subsequent updates beyond this length are silently ignored. No special handling of truncated updates is provided.

The underlying implementation may further limit the length of the length of the initial or subsequent value.

Access to the instrument is provided through the returned ByteBuffer object.

Parameters

name:String: the name of this entry.
variability:int: the variability characteristic for this entry.
units:int: the units for this entry.
value:byte[]: the initial value for this entry.
maxLength:int: the maximum length of this byte array.

Returns:ByteBuffer

ByteBuffer a direct allocated byte buffer that allows write access to a native memory location containing a long value. see sun.misc.perf.Variability see sun.misc.perf.Units

See Also

java.nio.ByteBuffer

createLong back to summary

createLong	back to summary
public native ByteBuffer createLong(String name, int variability, int units, long value) Create a `long` scalar entry in the instrumentation buffer with the given variability characteristic, units, and initial value. Access to the instrument is provided through the returned `ByteBuffer` object. Typically, this object should be wrapped with `LongBuffer` view object. Parameters name:String the name of this entry. variability:int the variability characteristic for this entry. units:int the units for this entry. value:long the initial value for this entry. Returns:ByteBuffer ByteBuffer a direct allocated ByteBuffer object that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units See Also `java.nio.ByteBuffer`

public native ByteBuffer createLong(String name, int variability, int units, long value)

Create a long scalar entry in the instrumentation buffer with the given variability characteristic, units, and initial value.

Access to the instrument is provided through the returned ByteBuffer object. Typically, this object should be wrapped with LongBuffer view object.

Parameters

name:String: the name of this entry.
variability:int: the variability characteristic for this entry.
units:int: the units for this entry.
value:long: the initial value for this entry.

Returns:ByteBuffer

ByteBuffer a direct allocated ByteBuffer object that allows write access to a native memory location containing a long value. see sun.misc.perf.Variability see sun.misc.perf.Units

See Also

java.nio.ByteBuffer

createString back to summary

createString	back to summary
public ByteBuffer createString(String name, int variability, int units, String value, int maxLength) Create a `String` entry in the instrumentation buffer with the given variability characteristic, units, and initial value. The maximum length of the `String` stored in this string instrument is given in by `maxLength` parameter. Updates to this instrument with `String` values with lengths greater than `maxLength` will be truncated to `maxLength`. The truncated value will be terminated by a null character. The underlying implementation may further limit the length of the value, but will continue to preserve the null terminator. Access to the instrument is provided through the returned `ByteBuffer` object. Parameters name:String the name of this entry. variability:int the variability characteristic for this entry. units:int the units for this entry. value:String the initial value for this entry. maxLength:int the maximum string length for this string instrument. Returns:ByteBuffer ByteBuffer a direct allocated ByteBuffer that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units See Also `java.nio.ByteBuffer`

public ByteBuffer createString(String name, int variability, int units, String value, int maxLength)

Create a String entry in the instrumentation buffer with the given variability characteristic, units, and initial value.

The maximum length of the String stored in this string instrument is given in by maxLength parameter. Updates to this instrument with String values with lengths greater than maxLength will be truncated to maxLength. The truncated value will be terminated by a null character.

The underlying implementation may further limit the length of the value, but will continue to preserve the null terminator.

Access to the instrument is provided through the returned ByteBuffer object.

Parameters

name:String: the name of this entry.
variability:int: the variability characteristic for this entry.
units:int: the units for this entry.
value:String: the initial value for this entry.
maxLength:int: the maximum string length for this string instrument.

Returns:ByteBuffer

ByteBuffer a direct allocated ByteBuffer that allows write access to a native memory location containing a long value. see sun.misc.perf.Variability see sun.misc.perf.Units

See Also

java.nio.ByteBuffer

createString back to summary

createString	back to summary
public ByteBuffer createString(String name, int variability, int units, String value) Create a `String` entry in the instrumentation buffer with the given variability characteristic, units, and initial value. The maximum length of the `String` stored in this string instrument is implied by the length of the `value` parameter. Subsequent updates to the value of this instrument will be truncated to this implied maximum length. The truncated value will be terminated by a null character. The underlying implementation may further limit the length of the initial or subsequent value, but will continue to preserve the null terminator. Access to the instrument is provided through the returned `ByteBuffer` object. Parameters name:String the name of this entry. variability:int the variability characteristic for this entry. units:int the units for this entry. value:String the initial value for this entry. Returns:ByteBuffer ByteBuffer a direct allocated ByteBuffer that allows write access to a native memory location containing a `long` value. see sun.misc.perf.Variability see sun.misc.perf.Units See Also `java.nio.ByteBuffer`

public ByteBuffer createString(String name, int variability, int units, String value)

Create a String entry in the instrumentation buffer with the given variability characteristic, units, and initial value.

The maximum length of the String stored in this string instrument is implied by the length of the value parameter. Subsequent updates to the value of this instrument will be truncated to this implied maximum length. The truncated value will be terminated by a null character.

The underlying implementation may further limit the length of the initial or subsequent value, but will continue to preserve the null terminator.

Access to the instrument is provided through the returned ByteBuffer object.

Parameters

name:String: the name of this entry.
variability:int: the variability characteristic for this entry.
units:int: the units for this entry.
value:String: the initial value for this entry.

Returns:ByteBuffer

ByteBuffer a direct allocated ByteBuffer that allows write access to a native memory location containing a long value. see sun.misc.perf.Variability see sun.misc.perf.Units

See Also

java.nio.ByteBuffer

detach back to summary

detach	back to summary
private native void detach(ByteBuffer bb) Native method to perform the implementation specific detach mechanism. If this method is passed a `ByteBuffer` object that is not created by the `attach` method, then the results of this method are undefined, with unpredictable and potentially damaging effects to the Java virtual machine. To prevent accidental or malicious use of this method, all native ByteBuffer created by the `attach` method are managed internally as PhantomReferences and resources are freed by the system. If this method is passed a `ByteBuffer` object created by the `attach` method with a lvmid for the Java virtual machine running this method (lvmid=0, for example), then the detach request is silently ignored. Parameters bb:ByteBuffer A direct allocated byte buffer created by the `attach` method. See Also `java.nio.ByteBuffer`, `attach`

private native void detach(ByteBuffer bb)

Native method to perform the implementation specific detach mechanism.

If this method is passed a ByteBuffer object that is not created by the attach method, then the results of this method are undefined, with unpredictable and potentially damaging effects to the Java virtual machine. To prevent accidental or malicious use of this method, all native ByteBuffer created by the attach method are managed internally as PhantomReferences and resources are freed by the system.

If this method is passed a ByteBuffer object created by the attach method with a lvmid for the Java virtual machine running this method (lvmid=0, for example), then the detach request is silently ignored.

Parameters

bb:ByteBuffer: A direct allocated byte buffer created by the attach method.

See Also

java.nio.ByteBuffer, attach

getPerf back to summary

getPerf	back to summary
public static Perf getPerf() Return a reference to the singleton Perf instance. The getPerf() method returns the singleton instance of the Perf class. The returned object provides the caller with the capability for accessing the instrumentation buffer for this or another local Java virtual machine. Access to the returned `Perf` object should be protected by its caller and not passed on to untrusted code. This object can be used to attach to the instrumentation buffer provided by this Java virtual machine or for those of other Java virtual machines running on the same system. The instrumentation buffer may contain senstitive information. API's built on top of this interface may want to provide finer grained access control to the contents of individual instrumentation objects contained within the buffer. Returns:Perf A reference to the singleton Perf instance. See Also `attach`

public static Perf getPerf()

Return a reference to the singleton Perf instance.

The getPerf() method returns the singleton instance of the Perf class. The returned object provides the caller with the capability for accessing the instrumentation buffer for this or another local Java virtual machine.

Access to the returned Perf object should be protected by its caller and not passed on to untrusted code. This object can be used to attach to the instrumentation buffer provided by this Java virtual machine or for those of other Java virtual machines running on the same system. The instrumentation buffer may contain senstitive information. API's built on top of this interface may want to provide finer grained access control to the contents of individual instrumentation objects contained within the buffer.

Returns:Perf: A reference to the singleton Perf instance.
See Also: attach

highResCounter back to summary

highResCounter	back to summary
public native long highResCounter() Return the value of the High Resolution Counter. The High Resolution Counter returns the number of ticks since since the start of the Java virtual machine. The resolution of the counter is machine dependent and can be determined from the value return by the `highResFrequency` method. Returns:long the number of ticks of machine dependent resolution since the start of the Java virtual machine. See Also `highResFrequency`, `java.lang.System#currentTimeMillis()`

public native long highResCounter()

Return the value of the High Resolution Counter. The High Resolution Counter returns the number of ticks since since the start of the Java virtual machine. The resolution of the counter is machine dependent and can be determined from the value return by the highResFrequency method.

Returns:long: the number of ticks of machine dependent resolution since the start of the Java virtual machine.
See Also: highResFrequency, java.lang.System#currentTimeMillis()

highResFrequency back to summary

highResFrequency	back to summary
public native long highResFrequency() Returns the frequency of the High Resolution Counter, in ticks per second. This value can be used to convert the value of the High Resolution Counter, as returned from a call to the `highResCounter` method, into the number of seconds since the start of the Java virtual machine. Returns:long the frequency of the High Resolution Counter. See Also `highResCounter`

public native long highResFrequency()

Returns the frequency of the High Resolution Counter, in ticks per second. This value can be used to convert the value of the High Resolution Counter, as returned from a call to the highResCounter method, into the number of seconds since the start of the Java virtual machine.

Returns:long: the frequency of the High Resolution Counter.
See Also: highResCounter

registerNatives	back to summary
private static native void registerNatives()

public final Class Perf

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private Class Perf.CleanerAction

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