add LazyFieldLite.java

java/src/main/java/com/google/protobuf/LazyFieldLite.java

+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// http://code.google.com/p/protobuf/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.google.protobuf;
+
+import java.io.IOException;
+
+/**
+ * LazyFieldLite encapsulates the logic of lazily parsing message fields. It stores
+ * the message in a ByteString initially and then parse it on-demand.
+ *
+ * LazyField is thread-compatible e.g. concurrent read are safe, however,
+ * synchronizations are needed under read/write situations.
+ *
+ * This class is internal implementation detail, so you don't need to use it directly.
+ *
+ * @author xiangl@google.com (Xiang Li)
+ */
+public class LazyFieldLite {
+  private ByteString bytes;
+  private ExtensionRegistryLite extensionRegistry;
+  private volatile boolean isDirty = false;
+
+  protected volatile MessageLite value;
+
+  public LazyFieldLite(ExtensionRegistryLite extensionRegistry, ByteString bytes) {
+    this.extensionRegistry = extensionRegistry;
+    this.bytes = bytes;
+  }
+
+  public LazyFieldLite() {
+  }
+
+  public static LazyFieldLite fromValue(MessageLite value) {
+    LazyFieldLite lf = new LazyFieldLite();
+    lf.setValue(value);
+    return lf;
+  }
+
+  public boolean containsDefaultInstance() {
+    return value == null && bytes == null;
+  }
+
+  public void clear() {
+    bytes = null;
+    value = null;
+    extensionRegistry = null;
+    isDirty = true;
+  }
+
+  /**
+   * Returns message instance. At first time, serialized data is parsed by
+   * {@code defaultInstance.getParserForType()}.
+   *
+   * @param defaultInstance its message's default instance. It's also used to get parser for the
+   * message type.
+   */
+  public MessageLite getValue(MessageLite defaultInstance) {
+    ensureInitialized(defaultInstance);
+    return value;
+  }
+
+  /**
+   * LazyField is not thread-safe for write access. Synchronizations are needed
+   * under read/write situations.
+   */
+  public MessageLite setValue(MessageLite value) {
+    MessageLite originalValue = this.value;
+    this.value = value;
+    bytes = null;
+    isDirty = true;
+    return originalValue;
+  }
+
+  public void merge(LazyFieldLite value) {
+    if (value.containsDefaultInstance()) {
+      return;
+    }
+
+    if (bytes == null) {
+      this.bytes = value.bytes;
+    } else {
+      this.bytes.concat(value.toByteString());
+    }
+    isDirty = false;
+  }
+
+  public void setByteString(ByteString bytes, ExtensionRegistryLite extensionRegistry) {
+    this.bytes = bytes;
+    this.extensionRegistry = extensionRegistry;
+    isDirty = false;
+  }
+
+  public ExtensionRegistryLite getExtensionRegistry() {
+    return extensionRegistry;
+  }
+
+  /**
+   * Due to the optional field can be duplicated at the end of serialized
+   * bytes, which will make the serialized size changed after LazyField
+   * parsed. Be careful when using this method.
+   */
+  public int getSerializedSize() {
+    if (isDirty) {
+      return value.getSerializedSize();
+    }
+    return bytes.size();
+  }
+
+  public ByteString toByteString() {
+    if (!isDirty) {
+      return bytes;
+    }
+    synchronized (this) {
+      if (!isDirty) {
+        return bytes;
+      }
+      if (value == null) {
+        bytes = ByteString.EMPTY;
+      } else {
+        bytes = value.toByteString();
+      }
+      isDirty = false;
+      return bytes;
+    }
+  }
+
+  protected void ensureInitialized(MessageLite defaultInstance) {
+    if (value != null) {
+      return;
+    }
+    synchronized (this) {
+      if (value != null) {
+        return;
+      }
+      try {
+        if (bytes != null) {
+          value = defaultInstance.getParserForType()
+              .parseFrom(bytes, extensionRegistry);
+        } else {
+          value = defaultInstance;
+        }
+      } catch (IOException e) {
+        // TODO(xiangl): Refactory the API to support the exception thrown from
+        // lazily load messages.
+      }
+    }
+  }
+}