From afb35a5d1be4a9718376098ef991496d5548dc4d Mon Sep 17 00:00:00 2001
From: lowasser <lowasser@google.com>
Date: Mon, 12 Feb 2024 13:48:46 -0800
Subject: [PATCH] Optimize checksum-based hash functions on non-array
 ByteBuffers by at least an order of magnitude, at least for Java 9+.

RELNOTES=`hash`: Optimized `Checksum`-based hash functions for Java 9+.
PiperOrigin-RevId: 606354141
---
 .../common/hash/ChecksumHashFunction.java     | 56 +++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/guava/src/com/google/common/hash/ChecksumHashFunction.java b/guava/src/com/google/common/hash/ChecksumHashFunction.java
index 159adbb8194b..454f3098e3ee 100644
--- a/guava/src/com/google/common/hash/ChecksumHashFunction.java
+++ b/guava/src/com/google/common/hash/ChecksumHashFunction.java
@@ -18,8 +18,14 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.google.errorprone.annotations.Immutable;
+import com.google.j2objc.annotations.J2ObjCIncompatible;
 import java.io.Serializable;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.nio.ByteBuffer;
 import java.util.zip.Checksum;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * {@link HashFunction} adapter for {@link Checksum} instances.
@@ -74,6 +80,14 @@ protected void update(byte[] bytes, int off, int len) {
       checksum.update(bytes, off, len);
     }
 
+    @Override
+    @J2ObjCIncompatible
+    protected void update(ByteBuffer b) {
+      if (!ChecksumMethodHandles.updateByteBuffer(checksum, b)) {
+        super.update(b);
+      }
+    }
+
     @Override
     public HashCode hash() {
       long value = checksum.getValue();
@@ -90,5 +104,47 @@ public HashCode hash() {
     }
   }
 
+  @J2ObjCIncompatible
+  @SuppressWarnings("unused")
+  private static final class ChecksumMethodHandles {
+    private static final @Nullable MethodHandle UPDATE_BB = updateByteBuffer();
+
+    @IgnoreJRERequirement // https://github.com/mojohaus/animal-sniffer/issues/67
+    static boolean updateByteBuffer(Checksum cs, ByteBuffer bb) {
+      if (UPDATE_BB != null) {
+        try {
+          UPDATE_BB.invokeExact(cs, bb);
+        } catch (Error t) {
+          throw t;
+        } catch (Throwable t) {
+          throw new AssertionError(t);
+        }
+        return true;
+      } else {
+        return false;
+      }
+    }
+
+    private static @Nullable MethodHandle updateByteBuffer() {
+      try {
+        Class<?> clazz = Class.forName("java.util.zip.Checksum");
+        return MethodHandles.lookup()
+            .findVirtual(clazz, "update", MethodType.methodType(void.class, ByteBuffer.class));
+      } catch (ClassNotFoundException e) {
+        throw new AssertionError(e);
+      } catch (IllegalAccessException e) {
+        // That API is public.
+        throw newLinkageError(e);
+      } catch (NoSuchMethodException e) {
+        // Only introduced in Java 9.
+        return null;
+      }
+    }
+
+    private static LinkageError newLinkageError(Throwable cause) {
+      return new LinkageError(cause.toString(), cause);
+    }
+  }
+
   private static final long serialVersionUID = 0L;
 }