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// Copyright 2017 The Bazel Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.lib.unsafe;
import java.lang.reflect.Field;
import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import sun.misc.Unsafe;
/**
* An accessor for Unsafe.
*
* <p>Not for general consumption. Public only so that generated codecs in different packages can
* access this.
*/
public class UnsafeProvider {
private static final Unsafe UNSAFE = getUnsafe();
public static Unsafe getInstance() {
return UNSAFE;
}
/**
* Gets a reference to {@link sun.misc.Unsafe} throwing an {@link AssertionError} on failure.
*
* <p>Failure is highly unlikely, but possible if the underlying VM stores unsafe in an unexpected
* location.
*/
private static Unsafe getUnsafe() {
try {
// sun.misc.Unsafe is intentionally difficult to get a hold of - it gives us the power to
// do things like access raw memory and segfault the JVM.
return AccessController.doPrivileged(
new PrivilegedExceptionAction<Unsafe>() {
@Override
public Unsafe run() throws Exception {
Class<Unsafe> unsafeClass = Unsafe.class;
// Unsafe usually exists in the field 'theUnsafe', however check all fields
// in case it's somewhere else in this VM's version of Unsafe.
for (Field f : unsafeClass.getDeclaredFields()) {
f.setAccessible(true);
Object fieldValue = f.get(null);
if (unsafeClass.isInstance(fieldValue)) {
return unsafeClass.cast(fieldValue);
}
}
throw new AssertionError("Failed to find sun.misc.Unsafe instance");
}
});
} catch (PrivilegedActionException pae) {
throw new AssertionError("Unable to get sun.misc.Unsafe", pae);
}
}
}
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