org.graalvm.nativeimage.hosted.RuntimeClassInitialization Maven / Gradle / Ivy
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package org.graalvm.nativeimage.hosted;
import org.graalvm.nativeimage.ImageSingletons;
import org.graalvm.nativeimage.Platform;
import org.graalvm.nativeimage.Platforms;
import org.graalvm.nativeimage.impl.RuntimeClassInitializationSupport;
/**
* This class provides methods that can be called during native-image building to configure class
* initialization behavior. By default, all JDK classes that are seen as reachable for a native
* image are initialized during image building, i.e. the class initialization method is executed
* during image building and is not seen as a reachable method at runtime. Application classes, on
* the other hand, are initialized during image building if they can be proven safe. Unsafe classes,
* e.g. ones that create threads, will be initialized at image run time.
*
* For classes that can't be proven safe, it is sometimes beneficial to ensure initialization during
* image building, and for some that are safe, it is still necessary to initialize at runtime (e.g.,
* the order of initializer execution matters).
*
* This class provides two different registration methods: Classes registered via
* {@link #initializeAtRunTime} are not initialized at all during image generation, and only
* initialized at runtime, i.e., the class initializer is executed once at runtime. Classes
* registered via {@link #initializeAtBuildTime} will be initialized during image building.
*
* It is also possible define initialization for whole packages with
* {@link #initializeAtRunTime(String[])} and {@link #initializeAtBuildTime(String[])}. The rules
* for packages can be further refined by using methods for individual classes.
*
* Initializing classes at runtime comes with some costs and restrictions:
*
* - The class initialization status must be checked before a static field access, static method
* call, and object allocation of such classes. This has an impact on performance.
* - Instances of such classes are not allowed on the image heap, i.e., on the initial heap that
* is part of the native executable. Otherwise instances would exist before the class is
* initialized, which violates the class initialization specification.
*
*
* @since 19.0
*/
@Platforms(Platform.HOSTED_ONLY.class)
public final class RuntimeClassInitialization {
/**
* Registers the provided classes, and all of their subclasses, for class initialization at
* runtime. The classes are not initialized automatically during image generation, and also must
* not be initialized manually by the user during image generation.
*
* Unfortunately, classes are initialized for many reasons, and it is not possible to intercept
* class initialization and report an error at this time. If a registered class gets
* initialized, an error can be reported only later and the user must manually debug the reason
* for class initialization. This can be done by, e.g., setting a breakpoint in the class
* initializer or adding debug printing (print the stack trace) in the class initializer.
*
* @since 19.0
*/
public static void initializeAtRunTime(Class... classes) {
StackTraceElement[] stacktrace = Thread.currentThread().getStackTrace();
for (Class aClass : classes) {
ImageSingletons.lookup(RuntimeClassInitializationSupport.class).initializeAtRunTime(aClass, classReason(stacktrace, getUnqualifiedName(aClass) + ".class"));
}
}
/**
* Registers the provided classes as eagerly initialized during image-build time.
*
* All static initializers of {@code classes} will be executed during image-build time and
* static fields that are assigned values will be available at runtime. {@code static final}
* fields will be considered as constant.
*
* It is up to the user to ensure that this behavior makes sense and does not lead to wrong
* application behavior.
*
* @since 19.0
*/
public static void initializeAtBuildTime(Class... classes) {
StackTraceElement[] stacktrace = Thread.currentThread().getStackTrace();
for (Class aClass : classes) {
ImageSingletons.lookup(RuntimeClassInitializationSupport.class).initializeAtBuildTime(aClass, classReason(stacktrace, getUnqualifiedName(aClass) + ".class"));
}
}
/**
* Registers all classes in provided packages, and all of their subclasses, for class
* initialization at runtime. The classes are not initialized automatically during image
* generation, and also must not be initialized manually by the user during image generation.
*
* Unfortunately, classes are initialized for many reasons, and it is not possible to intercept
* class initialization and report an error at this time. If a registered class gets
* initialized, an error can be reported only later and the user must manually debug the reason
* for class initialization. This can be done by, e.g., setting a breakpoint in the class
* initializer or adding debug printing (print the stack trace) in the class initializer.
*
* @since 19.0
*/
public static void initializeAtRunTime(String... packages) {
StackTraceElement[] stacktrace = Thread.currentThread().getStackTrace();
for (String aPackage : packages) {
ImageSingletons.lookup(RuntimeClassInitializationSupport.class).initializeAtRunTime(aPackage, classReason(stacktrace, aPackage));
}
}
/**
* Registers all classes in provided packages as eagerly initialized during image-build time.
*
* All static initializers of {@code classes} will be executed during image-build time and
* static fields that are assigned values will be available at runtime. {@code static final}
* fields will be considered as constant.
*
* It is up to the user to ensure that this behavior makes sense and does not lead to wrong
* application behavior.
*
* @since 19.0
*/
public static void initializeAtBuildTime(String... packages) {
StackTraceElement[] stacktrace = Thread.currentThread().getStackTrace();
for (String aPackage : packages) {
ImageSingletons.lookup(RuntimeClassInitializationSupport.class).initializeAtBuildTime(aPackage, classReason(stacktrace, aPackage));
}
}
private static String getCaller(StackTraceElement[] stackTrace) {
StackTraceElement e = stackTrace[2];
return e.getClassName() + "." + e.getMethodName();
}
private static String classReason(StackTraceElement[] stacktrace, String simpleName) {
return "from feature " + getCaller(stacktrace) + " with '" + simpleName + "'";
}
/**
* Alternative to {@link Class#getSimpleName} that does not probe the enclosing class or method
* which fails when they are not yet loaded. Duplicated from
* {@code ClassUtil.getUnqualifiedName} which is not reachable here.
*/
private static String getUnqualifiedName(Class aClass) {
String name = aClass.getTypeName();
return name.substring(name.lastIndexOf('.') + 1); // strip the package name
}
private RuntimeClassInitialization() {
}
}