com.google.protobuf.LazyFieldLite Maven / Gradle / Ivy
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
// https://developers.google.com/protocol-buffers/
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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 parses it on-demand.
*
* LazyFieldLite is thread-compatible: concurrent reads are safe once the proto that this
* LazyFieldLite is a part of is no longer being mutated by its Builder. However, explicit
* synchronization is needed under read/write situations.
*
*
When a LazyFieldLite is used in the context of a MessageLite object, its behavior is
* considered to be immutable and none of the setter methods in its API are expected to be invoked.
* All of the getters are expected to be thread-safe. When used in the context of a
* MessageLite.Builder, setters can be invoked, but there is no guarantee of thread safety.
*
*
TODO(yatin,dweis): Consider splitting this class's functionality and put the mutable methods
* into a separate builder class to allow us to give stronger compile-time guarantees.
*
*
This class is internal implementation detail of the protobuf library, so you don't need to use
* it directly.
*
* @author [email protected] (Xiang Li)
*/
public class LazyFieldLite {
private static final ExtensionRegistryLite EMPTY_REGISTRY =
ExtensionRegistryLite.getEmptyRegistry();
/*
* The value associated with the LazyFieldLite object is stored in one or more of the following
* three fields (delayedBytes, value, memoizedBytes). They should together be interpreted as
* follows.
*
* 1) delayedBytes can be non-null, while value and memoizedBytes is null. The object will be in
* this state while the value for the object has not yet been parsed.
*
* 2) Both delayedBytes and value are non-null. The object transitions to this state as soon as
* some caller needs to access the value (by invoking getValue()).
*
* 3) memoizedBytes is merely an optimization for calls to LazyFieldLite.toByteString() to avoid
* recomputing the ByteString representation on each call. Instead, when the value is parsed from
* delayedBytes, we will also assign the contents of delayedBytes to memoizedBytes (since that is
* the ByteString representation of value).
*
* 4) Finally, if the LazyFieldLite was created directly with a parsed MessageLite value, then
* delayedBytes will be null, and memoizedBytes will be initialized only upon the first call to
* LazyFieldLite.toByteString().
*
*
Given the above conditions, any caller that needs a serialized representation of this object
* must first check if the memoizedBytes or delayedBytes ByteString is non-null and use it
* directly; if both of those are null, it can look at the parsed value field. Similarly, any
* caller that needs a parsed value must first check if the value field is already non-null, if
* not it must parse the value from delayedBytes.
*/
/**
* A delayed-parsed version of the contents of this field. When this field is non-null, then the
* "value" field is allowed to be null until the time that the value needs to be read.
*
*
When delayedBytes is non-null then {@code extensionRegistry} is required to also be
* non-null. {@code value} and {@code memoizedBytes} will be initialized lazily.
*/
private ByteString delayedBytes;
/**
* An {@code ExtensionRegistryLite} for parsing bytes. It is non-null on a best-effort basis. It
* is only guaranteed to be non-null if this message was initialized using bytes and an {@code
* ExtensionRegistry}. If it directly had a value set then it will be null, unless it has been
* merged with another {@code LazyFieldLite} that had an {@code ExtensionRegistry}.
*/
private ExtensionRegistryLite extensionRegistry;
/**
* The parsed value. When this is null and a caller needs access to the MessageLite value, then
* {@code delayedBytes} will be parsed lazily at that time.
*/
protected volatile MessageLite value;
/**
* The memoized bytes for {@code value}. This is an optimization for the toByteString() method to
* not have to recompute its return-value on each invocation. TODO(yatin): Figure out whether this
* optimization is actually necessary.
*/
private volatile ByteString memoizedBytes;
/** Constructs a LazyFieldLite with bytes that will be parsed lazily. */
public LazyFieldLite(ExtensionRegistryLite extensionRegistry, ByteString bytes) {
checkArguments(extensionRegistry, bytes);
this.extensionRegistry = extensionRegistry;
this.delayedBytes = bytes;
}
/** Constructs a LazyFieldLite with no contents, and no ability to parse extensions. */
public LazyFieldLite() {}
/**
* Constructs a LazyFieldLite instance with a value. The LazyFieldLite may not be able to parse
* the extensions in the value as it has no ExtensionRegistry.
*/
public static LazyFieldLite fromValue(MessageLite value) {
LazyFieldLite lf = new LazyFieldLite();
lf.setValue(value);
return lf;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (!(o instanceof LazyFieldLite)) {
return false;
}
LazyFieldLite other = (LazyFieldLite) o;
// Lazy fields do not work well with equals... If both are delayedBytes, we do not have a
// mechanism to deserialize them so we rely on bytes equality. Otherwise we coerce into an
// actual message (if necessary) and call equals on the message itself. This implies that two
// messages can by unequal but then be turned equal simply be invoking a getter on a lazy field.
MessageLite value1 = value;
MessageLite value2 = other.value;
if (value1 == null && value2 == null) {
return toByteString().equals(other.toByteString());
} else if (value1 != null && value2 != null) {
return value1.equals(value2);
} else if (value1 != null) {
return value1.equals(other.getValue(value1.getDefaultInstanceForType()));
} else {
return getValue(value2.getDefaultInstanceForType()).equals(value2);
}
}
@Override
public int hashCode() {
// We can't provide a memoizable hash code for lazy fields. The byte strings may have different
// hash codes but evaluate to equivalent messages. And we have no facility for constructing
// a message here if we were not already holding a value.
return 1;
}
/**
* Determines whether this LazyFieldLite instance represents the default instance of this type.
*/
public boolean containsDefaultInstance() {
return memoizedBytes == ByteString.EMPTY
|| value == null && (delayedBytes == null || delayedBytes == ByteString.EMPTY);
}
/**
* Clears the value state of this instance.
*
*
LazyField is not thread-safe for write access. Synchronizations are needed under read/write
* situations.
*/
public void clear() {
// Don't clear the ExtensionRegistry. It might prove useful later on when merging in another
// value, but there is no guarantee that it will contain all extensions that were directly set
// on the values that need to be merged.
delayedBytes = null;
value = null;
memoizedBytes = null;
}
/**
* Overrides the contents of this LazyField.
*
*
LazyField is not thread-safe for write access. Synchronizations are needed under read/write
* situations.
*/
public void set(LazyFieldLite other) {
this.delayedBytes = other.delayedBytes;
this.value = other.value;
this.memoizedBytes = other.memoizedBytes;
// If the other LazyFieldLite was created by directly setting the value rather than first by
// parsing, then it will not have an extensionRegistry. In this case we hold on to the existing
// extensionRegistry, which has no guarantees that it has all the extensions that will be
// directly set on the value.
if (other.extensionRegistry != null) {
this.extensionRegistry = other.extensionRegistry;
}
}
/**
* Returns message instance. It may do some thread-safe delayed parsing of bytes.
*
* @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;
}
/**
* Sets the value of the instance and returns the old value without delay parsing anything.
*
*
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.delayedBytes = null;
this.memoizedBytes = null;
this.value = value;
return originalValue;
}
/**
* Merges another instance's contents. In some cases may drop some extensions if both fields
* contain data. If the other field has an {@code ExtensionRegistry} but this does not, then this
* field will copy over that {@code ExtensionRegistry}.
*
*
LazyField is not thread-safe for write access. Synchronizations are needed under read/write
* situations.
*/
public void merge(LazyFieldLite other) {
if (other.containsDefaultInstance()) {
return;
}
if (this.containsDefaultInstance()) {
set(other);
return;
}
// If the other field has an extension registry but this does not, copy over the other extension
// registry.
if (this.extensionRegistry == null) {
this.extensionRegistry = other.extensionRegistry;
}
// In the case that both of them are not parsed we simply concatenate the bytes to save time. In
// the (probably rare) case that they have different extension registries there is a chance that
// some of the extensions may be dropped, but the tradeoff of making this operation fast seems
// to outway the benefits of combining the extension registries, which is not normally done for
// lite protos anyways.
if (this.delayedBytes != null && other.delayedBytes != null) {
this.delayedBytes = this.delayedBytes.concat(other.delayedBytes);
return;
}
// At least one is parsed and both contain data. We won't drop any extensions here directly, but
// in the case that the extension registries are not the same then we might in the future if we
// need to serialize and parse a message again.
if (this.value == null && other.value != null) {
setValue(mergeValueAndBytes(other.value, this.delayedBytes, this.extensionRegistry));
return;
} else if (this.value != null && other.value == null) {
setValue(mergeValueAndBytes(this.value, other.delayedBytes, other.extensionRegistry));
return;
}
// At this point we have two fully parsed messages.
setValue(this.value.toBuilder().mergeFrom(other.value).build());
}
/**
* Merges another instance's contents from a stream.
*
*
LazyField is not thread-safe for write access. Synchronizations are needed under read/write
* situations.
*/
public void mergeFrom(CodedInputStream input, ExtensionRegistryLite extensionRegistry)
throws IOException {
if (this.containsDefaultInstance()) {
setByteString(input.readBytes(), extensionRegistry);
return;
}
// If the other field has an extension registry but this does not, copy over the other extension
// registry.
if (this.extensionRegistry == null) {
this.extensionRegistry = extensionRegistry;
}
// In the case that both of them are not parsed we simply concatenate the bytes to save time. In
// the (probably rare) case that they have different extension registries there is a chance that
// some of the extensions may be dropped, but the tradeoff of making this operation fast seems
// to outway the benefits of combining the extension registries, which is not normally done for
// lite protos anyways.
if (this.delayedBytes != null) {
setByteString(this.delayedBytes.concat(input.readBytes()), this.extensionRegistry);
return;
}
// We are parsed and both contain data. We won't drop any extensions here directly, but in the
// case that the extension registries are not the same then we might in the future if we
// need to serialize and parse a message again.
try {
setValue(value.toBuilder().mergeFrom(input, extensionRegistry).build());
} catch (InvalidProtocolBufferException e) {
// Nothing is logged and no exceptions are thrown. Clients will be unaware that a proto
// was invalid.
}
}
private static MessageLite mergeValueAndBytes(
MessageLite value, ByteString otherBytes, ExtensionRegistryLite extensionRegistry) {
try {
return value.toBuilder().mergeFrom(otherBytes, extensionRegistry).build();
} catch (InvalidProtocolBufferException e) {
// Nothing is logged and no exceptions are thrown. Clients will be unaware that a proto
// was invalid.
return value;
}
}
/** Sets this field with bytes to delay-parse. */
public void setByteString(ByteString bytes, ExtensionRegistryLite extensionRegistry) {
checkArguments(extensionRegistry, bytes);
this.delayedBytes = bytes;
this.extensionRegistry = extensionRegistry;
this.value = null;
this.memoizedBytes = null;
}
/**
* 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() {
// We *must* return delayed bytes size if it was ever set because the dependent messages may
// have memoized serialized size based off of it.
if (memoizedBytes != null) {
return memoizedBytes.size();
} else if (delayedBytes != null) {
return delayedBytes.size();
} else if (value != null) {
return value.getSerializedSize();
} else {
return 0;
}
}
/** Returns a BytesString for this field in a thread-safe way. */
public ByteString toByteString() {
if (memoizedBytes != null) {
return memoizedBytes;
}
// We *must* return delayed bytes if it was set because the dependent messages may have
// memoized serialized size based off of it.
if (delayedBytes != null) {
return delayedBytes;
}
synchronized (this) {
if (memoizedBytes != null) {
return memoizedBytes;
}
if (value == null) {
memoizedBytes = ByteString.EMPTY;
} else {
memoizedBytes = value.toByteString();
}
return memoizedBytes;
}
}
/** Writes this lazy field into a {@link Writer}. */
void writeTo(Writer writer, int fieldNumber) throws IOException {
if (memoizedBytes != null) {
writer.writeBytes(fieldNumber, memoizedBytes);
} else if (delayedBytes != null) {
writer.writeBytes(fieldNumber, delayedBytes);
} else if (value != null) {
writer.writeMessage(fieldNumber, value);
} else {
writer.writeBytes(fieldNumber, ByteString.EMPTY);
}
}
/** Might lazily parse the bytes that were previously passed in. Is thread-safe. */
protected void ensureInitialized(MessageLite defaultInstance) {
if (value != null) {
return;
}
synchronized (this) {
if (value != null) {
return;
}
try {
if (delayedBytes != null) {
// The extensionRegistry shouldn't be null here since we have delayedBytes.
MessageLite parsedValue =
defaultInstance.getParserForType().parseFrom(delayedBytes, extensionRegistry);
this.value = parsedValue;
this.memoizedBytes = delayedBytes;
} else {
this.value = defaultInstance;
this.memoizedBytes = ByteString.EMPTY;
}
} catch (InvalidProtocolBufferException e) {
// Nothing is logged and no exceptions are thrown. Clients will be unaware that this proto
// was invalid.
this.value = defaultInstance;
this.memoizedBytes = ByteString.EMPTY;
}
}
}
private static void checkArguments(ExtensionRegistryLite extensionRegistry, ByteString bytes) {
if (extensionRegistry == null) {
throw new NullPointerException("found null ExtensionRegistry");
}
if (bytes == null) {
throw new NullPointerException("found null ByteString");
}
}
}