"private static Class clazz = SnappyDecompressor.class" 源文件中的 clazz 有什么用？

Question

我正在研究 Snappy、Zlib 和其他压缩器的实现（在 Java 中）。靠近源文件顶部的是下面这一行。谁能给我解释一下这是什么意思？

HACK - Use this as a global lock in the JNI layer
@SuppressWarnings({"unchecked", "unused"})
private static Class clazz = SnappyDecompressor.class;

据我了解，例如，在 Snappy 中，SnappyDecompressor.java 本质上是一个用于 snappy C/native 实现的包装器，为了调用该 C 实现，Java 层通过 JNI 进行调用界面。

snappy（Java 包装器）源代码的顶部，SnappyDecompressor.java 在这里：

package org.apache.hadoop.io.compress.snappy;
import java.io.IOException;
import java.nio.Buffer;
import java.nio.ByteBuffer;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.compress.Decompressor;

/**
 * A {@link Decompressor} based on the snappy compression algorithm.
 * http://code.google.com/p/snappy/
 */
public class SnappyDecompressor implements Decompressor {
  private static final Log LOG =
      LogFactory.getLog(SnappyCompressor.class.getName());
  private static final int DEFAULT_DIRECT_BUFFER_SIZE = 64 * 1024;

  // HACK - Use this as a global lock in the JNI layer
  @SuppressWarnings({"unchecked", "unused"})
  private static Class clazz = SnappyDecompressor.class;

Full source

Answer 1

如评论中所述：它是从JNI层使用的，似乎是为了JNI层的一些锁定。 (see the full Decompressor source)

第 76、77 行：

SnappyDecompressor_clazz = (*env)->GetStaticFieldID(env, clazz, "clazz",
                                                 "Ljava/lang/Class;");

第 83 行：

jobject clazz = (*env)->GetStaticObjectField(env,thisj, SnappyDecompressor_clazz);

第 100 至 102 行：

LOCK_CLASS(env, clazz, "SnappyDecompressor");
const char* compressed_bytes = (const char*)(*env)->GetDirectBufferAddress(env, compressed_direct_buf);
UNLOCK_CLASS(env, clazz, "SnappyDecompressor");

"private static Class clazz = SnappyDecompressor.class" 源文件中的 clazz 有什么用？

What is clazz used for in "private static Class clazz = SnappyDecompressor.class" source file?

java

java-native-interface

hadoop

native