com.oracle.svm.core.threadlocal

Class FastThreadLocalFactory

java.lang.Object

com.oracle.svm.core.threadlocal.FastThreadLocalFactory

public final class FastThreadLocalFactory
extends Object

This class contains factory methods to create fast thread local variables. A thread local variable is represented as an object, with different classes for primitive int (class FastThreadLocalInt), primitive long (class FastThreadLocalLong), Object (class FastThreadLocalObject), and word (class FastThreadLocalWord) values. Access to such thread local variables is significantly faster than regular Java ThreadLocal variables. However, there are several restrictions:

• The thread local object must be created during native image generation. Otherwise, the size of the IsolateThread data structure would not be a compile time constant.
• It is not possible to access the value of a thread local variable during native image generation. Attempts to do so will result in an error during native image generation.
• The initial value of a thread local variable is 0 or null for every newly created thread. There is no possibility to specify an initial value.
• A thread local variable created by this factory must be assigned to one static final field. The name of that field is used as the name of the local variable. The name is used to sort the variables in the IsolateThread data structure, to make the layout deterministic and reproducible.
• When accessing the value, the thread local variable must be a compile time constant. This is fulfilled when the value is accessed from the static final field, which is the intended use case.
• Thread locals of other threads may only be accessed at a safepoint. This restriction is necessary as the other thread could otherwise exit at any time, which frees the memory of the thread locals.

The implementation of fast thread local variables and the way the data is stored is implementation specific and transparent for users of it. However, the access is fast and never requires object allocation.

Method Summary

Modifier and Type	Method and Description
static <T extends org.graalvm.word.PointerBase> FastThreadLocalBytes<T>	createBytes(IntSupplier sizeSupplier, String name) Creates a new fast thread local memory block that has a user-defined size.
static FastThreadLocalInt	createInt(String name) Creates a new fast thread local variable of the primitive type int.
static FastThreadLocalLong	createLong(String name) Creates a new fast thread local variable of the primitive type long.
static <T> FastThreadLocalObject<T>	createObject(Class<T> valueClass, String name) Creates a new fast thread local variable of type Object.
static <T extends org.graalvm.word.WordBase> FastThreadLocalWord<T>	createWord(String name) Creates a new fast thread local variable of type word.

Methods inherited from class java.lang.Object

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

Method Detail

createInt

public static FastThreadLocalInt createInt(String name)

Creates a new fast thread local variable of the primitive type int.

createLong

public static FastThreadLocalLong createLong(String name)

Creates a new fast thread local variable of the primitive type long.

createWord

public static <T extends org.graalvm.word.WordBase> FastThreadLocalWord<T> createWord(String name)

Creates a new fast thread local variable of type word.

createObject

public static <T> FastThreadLocalObject<T> createObject(Class<T> valueClass,
                                                        String name)

Creates a new fast thread local variable of type Object.

createBytes

public static <T extends org.graalvm.word.PointerBase> FastThreadLocalBytes<T> createBytes(IntSupplier sizeSupplier,
                                                                                           String name)

Creates a new fast thread local memory block that has a user-defined size.