1 // Protocol Buffers - Google's data interchange format
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30 
31 package com.google.protobuf;
32 
33 import java.io.IOException;
34 
35 /**
36  * LazyFieldLite encapsulates the logic of lazily parsing message fields. It stores
37  * the message in a ByteString initially and then parse it on-demand.
38  *
39  * LazyField is thread-compatible e.g. concurrent read are safe, however,
40  * synchronizations are needed under read/write situations.
41  *
42  * This class is internal implementation detail, so you don't need to use it directly.
43  *
44  * @author xiangl@google.com (Xiang Li)
45  */
46 public class LazyFieldLite {
47   private ByteString bytes;
48   private ExtensionRegistryLite extensionRegistry;
49   private volatile boolean isDirty = false;
50 
51   protected volatile MessageLite value;
52 
LazyFieldLite(ExtensionRegistryLite extensionRegistry, ByteString bytes)53   public LazyFieldLite(ExtensionRegistryLite extensionRegistry, ByteString bytes) {
54     this.extensionRegistry = extensionRegistry;
55     this.bytes = bytes;
56   }
57 
LazyFieldLite()58   public LazyFieldLite() {
59   }
60 
fromValue(MessageLite value)61   public static LazyFieldLite fromValue(MessageLite value) {
62     LazyFieldLite lf = new LazyFieldLite();
63     lf.setValue(value);
64     return lf;
65   }
66 
containsDefaultInstance()67   public boolean containsDefaultInstance() {
68     return value == null && bytes == null;
69   }
70 
clear()71   public void clear() {
72     bytes = null;
73     value = null;
74     extensionRegistry = null;
75     isDirty = true;
76   }
77 
78   /**
79    * Returns message instance. At first time, serialized data is parsed by
80    * {@code defaultInstance.getParserForType()}.
81    *
82    * @param defaultInstance its message's default instance. It's also used to get parser for the
83    * message type.
84    */
getValue(MessageLite defaultInstance)85   public MessageLite getValue(MessageLite defaultInstance) {
86     ensureInitialized(defaultInstance);
87     return value;
88   }
89 
90   /**
91    * LazyField is not thread-safe for write access. Synchronizations are needed
92    * under read/write situations.
93    */
setValue(MessageLite value)94   public MessageLite setValue(MessageLite value) {
95     MessageLite originalValue = this.value;
96     this.value = value;
97     bytes = null;
98     isDirty = true;
99     return originalValue;
100   }
101 
merge(LazyFieldLite value)102   public void merge(LazyFieldLite value) {
103     if (value.containsDefaultInstance()) {
104       return;
105     }
106 
107     if (bytes == null) {
108       this.bytes = value.bytes;
109     } else {
110       this.bytes.concat(value.toByteString());
111     }
112     isDirty = false;
113   }
114 
setByteString(ByteString bytes, ExtensionRegistryLite extensionRegistry)115   public void setByteString(ByteString bytes, ExtensionRegistryLite extensionRegistry) {
116     this.bytes = bytes;
117     this.extensionRegistry = extensionRegistry;
118     isDirty = false;
119   }
120 
getExtensionRegistry()121   public ExtensionRegistryLite getExtensionRegistry() {
122     return extensionRegistry;
123   }
124 
125   /**
126    * Due to the optional field can be duplicated at the end of serialized
127    * bytes, which will make the serialized size changed after LazyField
128    * parsed. Be careful when using this method.
129    */
getSerializedSize()130   public int getSerializedSize() {
131     if (isDirty) {
132       return value.getSerializedSize();
133     }
134     return bytes.size();
135   }
136 
toByteString()137   public ByteString toByteString() {
138     if (!isDirty) {
139       return bytes;
140     }
141     synchronized (this) {
142       if (!isDirty) {
143         return bytes;
144       }
145       if (value == null) {
146         bytes = ByteString.EMPTY;
147       } else {
148         bytes = value.toByteString();
149       }
150       isDirty = false;
151       return bytes;
152     }
153   }
154 
ensureInitialized(MessageLite defaultInstance)155   protected void ensureInitialized(MessageLite defaultInstance) {
156     if (value != null) {
157       return;
158     }
159     synchronized (this) {
160       if (value != null) {
161         return;
162       }
163       try {
164         if (bytes != null) {
165           value = defaultInstance.getParserForType()
166               .parseFrom(bytes, extensionRegistry);
167         } else {
168           value = defaultInstance;
169         }
170       } catch (IOException e) {
171         // TODO(xiangl): Refactory the API to support the exception thrown from
172         // lazily load messages.
173       }
174     }
175   }
176 }
177