Package io.perfmark.impl

Class Generator

java.lang.Object

io.perfmark.impl.Generator

Direct Known Subclasses:

SecretGenerator.MethodHandleGenerator, SecretGenerator.VarHandleGenerator, SecretGenerator.VolatileGenerator

public class Generator
extends Object

A Generator keeps track of what generation the PerfMark library is on. A generation is a way to group PerfMark recorded tasks and links together. This allows dynamically enabling and disabling PerfMark. Each time the library is enabled, a new generation is started and associated with all the recorded data.

This class is not threadsafe. Synchronization is handled externally.

Normal users are not expected to use this class.

Field Summary

Fields

Modifier and Type	Field	Description
static final long	FAILURE	Represents a failure to enable PerfMark library.
static final int	GEN_OFFSET	The number of reserved bits at the bottom of the generation.
(package private) static final long	INIT_CURRENT_TIME_MILLIS	This field is also here as a hack, capturing the time the class loaded.
(package private) static final long	INIT_NANO_TIME	This field is here as a hack.
(package private) static final long	NO_NANO_TIME

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	Generator()

Method Summary

Modifier and Type	Method	Description
long	costOfGetNanos()	Returns the approximate cost to read the generation.
long	costOfSetNanos()	Returns the approximate cost to change the generation.
long	getGeneration()	Gets the current generation, shifted left by GEN_OFFSET.
void	setGeneration(long generation)	Sets the current generation count.

Methods inherited from class java.lang.Object

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

Field Details

INIT_NANO_TIME

static final long INIT_NANO_TIME

This field is here as a hack. This class is a shared dependency of both SecretPerfMarkImpl and Storage. The impl needs to record the first time an event occurs, but doesn't call Storage#clinit until PerfMark is enabled. This leads to the timings being off in the trace event viewer, since the "start" time is since it was enabled, rather than when the first PerfMark call happens.

NO_NANO_TIME

static final long NO_NANO_TIME

INIT_CURRENT_TIME_MILLIS

static final long INIT_CURRENT_TIME_MILLIS

This field is also here as a hack, capturing the time the class loaded.

GEN_OFFSET

public static final int GEN_OFFSET

The number of reserved bits at the bottom of the generation. All generations should be left-shifted by this amount.

See Also:

• Constant Field Values

FAILURE

public static final long FAILURE

Represents a failure to enable PerfMark library. This can be used by subclasses to indicate a previous failure to set the generation. It can also be used to indicate the generation count has overflowed.

See Also:

• Constant Field Values

Constructor Details

Generator

protected Generator()

Method Details

setGeneration

public void setGeneration(long generation)

Sets the current generation count. This should be eventually noticeable for callers of getGeneration(). An odd number means the library is enabled, while an even number means the library is disabled.

Parameters:

generation - the generation id, shifted left by GEN_OFFSET.

getGeneration

public long getGeneration()

Gets the current generation, shifted left by GEN_OFFSET. An odd number means the library is enabled, while an even number means the library is disabled.

Returns:

the current generation or FAILURE.

costOfSetNanos

public long costOfSetNanos()

Returns the approximate cost to change the generation.

Returns:

an approximate number of nanoseconds needed to change the generator value.

costOfGetNanos

public long costOfGetNanos()

Returns the approximate cost to read the generation.

Returns:

an approximate number of nanoseconds needed to read the generator value.