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Standard library for the Scala Programming Language

There is a newer version: 2.13.13

/*
 * Scala (https://www.scala-lang.org)
 *
 * Copyright EPFL and Lightbend, Inc.
 *
 * Licensed under Apache License 2.0
 * (http://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

package scala.collection.immutable;


import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.Field;

// Backport from scala.runtime moved into s.c.immutable and made package private to
// avoid the need for MiMa whitelisting.
/* package */ abstract class VM {
  static void releaseFence() throws Throwable {
    RELEASE_FENCE.invoke();
  }

  private VM() {
  }

  static final MethodHandle RELEASE_FENCE;

  static {
    RELEASE_FENCE = mkHandle();
  }

  private static MethodHandle mkHandle() {
    MethodHandles.Lookup lookup = MethodHandles.lookup();
    try {
      return lookup.findStatic(Class.forName("java.lang.invoke.VarHandle"), "releaseFence", MethodType.methodType(Void.TYPE));
    } catch (ClassNotFoundException e) {
      try {
        Class unsafeClass = Class.forName("sun.misc.Unsafe");
        return lookup.findVirtual(unsafeClass, "storeFence", MethodType.methodType(void.class)).bindTo(findUnsafe(unsafeClass));
      } catch (NoSuchMethodException | ClassNotFoundException | IllegalAccessException e1) {
        ExceptionInInitializerError error = new ExceptionInInitializerError(e1);
        error.addSuppressed(e);
        throw error;
      }
    } catch (NoSuchMethodException | IllegalAccessException e) {
      throw new ExceptionInInitializerError(e);
    }
  }

  private static Object findUnsafe(Class unsafeClass) throws IllegalAccessException {
    Object found = null;
    for (Field field : unsafeClass.getDeclaredFields()) {
      if (field.getType() == unsafeClass) {
        field.setAccessible(true);
        found = field.get(null);
        break;
      }
    }
    if (found == null) throw new IllegalStateException("No instance of Unsafe found");
    return found;
  }
}