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// 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;
import java.util.Iterator;
import java.util.Map.Entry;
/**
* LazyField 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.
*
* Now LazyField is only used to lazily load MessageSet.
* TODO(xiangl): Use LazyField to lazily load all messages.
*
* @author xiangl@google.com (Xiang Li)
*/
class LazyField {
final private MessageLite defaultInstance;
final private ExtensionRegistryLite extensionRegistry;
// Mutable because it is initialized lazily.
private ByteString bytes;
private volatile MessageLite value;
private volatile boolean isDirty = false;
public LazyField(MessageLite defaultInstance,
ExtensionRegistryLite extensionRegistry, ByteString bytes) {
this.defaultInstance = defaultInstance;
this.extensionRegistry = extensionRegistry;
this.bytes = bytes;
}
public MessageLite getValue() {
ensureInitialized();
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;
}
/**
* 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;
}
bytes = value.toByteString();
isDirty = false;
return bytes;
}
}
@Override
public int hashCode() {
ensureInitialized();
return value.hashCode();
}
@Override
public boolean equals(Object obj) {
ensureInitialized();
return value.equals(obj);
}
@Override
public String toString() {
ensureInitialized();
return value.toString();
}
private void ensureInitialized() {
if (value != null) {
return;
}
synchronized (this) {
if (value != null) {
return;
}
try {
if (bytes != null) {
value = defaultInstance.getParserForType()
.parseFrom(bytes, extensionRegistry);
}
} catch (IOException e) {
// TODO(xiangl): Refactory the API to support the exception thrown from
// lazily load messages.
}
}
}
// ====================================================
/**
* LazyEntry and LazyIterator are used to encapsulate the LazyField, when
* users iterate all fields from FieldSet.
*/
static class LazyEntry<K> implements Entry<K, Object> {
private Entry<K, LazyField> entry;
private LazyEntry(Entry<K, LazyField> entry) {
this.entry = entry;
}
public K getKey() {
return entry.getKey();
}
public Object getValue() {
LazyField field = entry.getValue();
if (field == null) {
return null;
}
return field.getValue();
}
public LazyField getField() {
return entry.getValue();
}
public Object setValue(Object value) {
if (!(value instanceof MessageLite)) {
throw new IllegalArgumentException(
"LazyField now only used for MessageSet, "
+ "and the value of MessageSet must be an instance of MessageLite");
}
return entry.getValue().setValue((MessageLite) value);
}
}
static class LazyIterator<K> implements Iterator<Entry<K, Object>> {
private Iterator<Entry<K, Object>> iterator;
public LazyIterator(Iterator<Entry<K, Object>> iterator) {
this.iterator = iterator;
}
public boolean hasNext() {
return iterator.hasNext();
}
@SuppressWarnings("unchecked")
public Entry<K, Object> next() {
Entry<K, ?> entry = iterator.next();
if (entry.getValue() instanceof LazyField) {
return new LazyEntry<K>((Entry<K, LazyField>) entry);
}
return (Entry<K, Object>) entry;
}
public void remove() {
iterator.remove();
}
}
}
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