jni: uniformly use GetByteArrayRegion() to copy bytes (#9380)

Summary:
Uniformly use GetByteArrayRegion() instead of GetByteArrayElements()
to copy bytes.
In addition, it can avoid an inefficient ReleaseByteArrayElements()
operation.
Some benefits of GetByteArrayRegion() can be referred to:
https://stackoverflow.com/a/2480493

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9380

Reviewed By: ajkr

Differential Revision: D35135474

Pulled By: jay-zhuang

fbshipit-source-id: a32c1774d37f2d22b9bcd105d83e0bb984b71b54

java/rocksjni/rocksjni.cc

@@ -829,9 +829,11 @@ bool rocksdb_single_delete_helper(
     const ROCKSDB_NAMESPACE::WriteOptions& write_options,
     ROCKSDB_NAMESPACE::ColumnFamilyHandle* cf_handle, jbyteArray jkey,
     jint jkey_len) {
-  jbyte* key = env->GetByteArrayElements(jkey, nullptr);
+  jbyte* key = new jbyte[jkey_len];
-  if (key == nullptr) {
+  env->GetByteArrayRegion(jkey, 0, jkey_len, key);
-    // exception thrown: OutOfMemoryError
+  if (env->ExceptionCheck()) {
+    // exception thrown: ArrayIndexOutOfBoundsException
+    delete[] key;
     return false;
   }
   ROCKSDB_NAMESPACE::Slice key_slice(reinterpret_cast<char*>(key), jkey_len);
@@ -844,10 +846,7 @@ bool rocksdb_single_delete_helper(
     s = db->SingleDelete(write_options, key_slice);
   }
 
-  // trigger java unref on key and value.
+  delete[] key;
-  // by passing JNI_ABORT, it will simply release the reference without
-  // copying the result back to the java byte array.
-  env->ReleaseByteArrayElements(jkey, key, JNI_ABORT);
 
   if (s.ok()) {
     return true;

java/rocksjni/write_batch_with_index.cc

@@ -735,9 +735,11 @@ void Java_org_rocksdb_WBWIRocksIterator_seek0(JNIEnv* env, jobject /*jobj*/,
                                               jlong handle, jbyteArray jtarget,
                                               jint jtarget_len) {
   auto* it = reinterpret_cast<ROCKSDB_NAMESPACE::WBWIIterator*>(handle);
-  jbyte* target = env->GetByteArrayElements(jtarget, nullptr);
+  jbyte* target = new jbyte[jtarget_len];
-  if (target == nullptr) {
+  env->GetByteArrayRegion(jtarget, 0, jtarget_len, target);
-    // exception thrown: OutOfMemoryError
+  if (env->ExceptionCheck()) {
+    // exception thrown: ArrayIndexOutOfBoundsException
+    delete[] target;
     return;
   }
 
@@ -746,7 +748,7 @@ void Java_org_rocksdb_WBWIRocksIterator_seek0(JNIEnv* env, jobject /*jobj*/,
 
   it->Seek(target_slice);
 
-  env->ReleaseByteArrayElements(jtarget, target, JNI_ABORT);
+  delete[] target;
 }
 
 /*
@@ -803,9 +805,11 @@ void Java_org_rocksdb_WBWIRocksIterator_seekForPrev0(JNIEnv* env,
                                                      jbyteArray jtarget,
                                                      jint jtarget_len) {
   auto* it = reinterpret_cast<ROCKSDB_NAMESPACE::WBWIIterator*>(handle);
-  jbyte* target = env->GetByteArrayElements(jtarget, nullptr);
+  jbyte* target = new jbyte[jtarget_len];
-  if (target == nullptr) {
+  env->GetByteArrayRegion(jtarget, 0, jtarget_len, target);
-    // exception thrown: OutOfMemoryError
+  if (env->ExceptionCheck()) {
+    // exception thrown: ArrayIndexOutOfBoundsException
+    delete[] target;
     return;
   }
 
@@ -814,7 +818,7 @@ void Java_org_rocksdb_WBWIRocksIterator_seekForPrev0(JNIEnv* env,
 
   it->SeekForPrev(target_slice);
 
-  env->ReleaseByteArrayElements(jtarget, target, JNI_ABORT);
+  delete[] target;
 }
 
 /*