Use unsafe String operations when writing parameter files.

When a LATIN-1 parameter file is requested, we can take advantage of the fact that JDK9 strings are (usually) stored as LATIN-1.

For UTF-8, we can still optimize for the common case where a LATIN-1 string contains only ASCII characters, as these are bit-identical between UTF-8 and LATIN-1. This would still be expected to be the vast majority of parameter file contents.

RELNOTES: None
PiperOrigin-RevId: 199816430

1 files changed, 68 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/unsafe/UnsafeProvider.java b/src/main/java/com/google/devtools/build/lib/unsafe/UnsafeProvider.java
new file mode 100644
index 0000000000..c1e3f3b87f
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/unsafe/UnsafeProvider.java
@@ -0,0 +1,68 @@
+// 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);
+    }
+  }
+}