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[Java][FlexBuffers] Abstract buffer access from ByteBuffer (#5743)

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To read and build flexbuffers on Java, one needs to wrap the data
using  ByteBuffer. But for the common case of having ByteBuffers
backed by arrays, accessing from a ByteBuffer might be inefficient.

So this change introduces two interfaces: ReadBuf and ReadWriteBuf.
It allows one to read and writes data directly on an array. It also allow
 other buffer implementations to be used with flexbuffers.

Another change is that FlexBuffersBuilder backed by array allows
the buffer to grow with the increase of the message size. Something
that could not be done with ByteBuffer.
This commit is contained in:
Paulo Pinheiro
2020-02-21 20:46:40 +01:00
committed by GitHub
parent 3ec7a53c62
commit cd88e6b2aa
8 changed files with 712 additions and 55 deletions
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49
java/com/google/flatbuffers/FlexBuffersBuilder.java
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@@ -83,7 +83,7 @@ public class FlexBuffersBuilder {
private static final int WIDTH_16 = 1;
private static final int WIDTH_32 = 2;
private static final int WIDTH_64 = 3;
private final ByteBuffer bb;
private final ReadWriteBuf bb;
private final ArrayList<Value> stack = new ArrayList<>();
private final HashMap<String, Integer> keyPool = new HashMap<>();
private final HashMap<String, Integer> stringPool = new HashMap<>();
@@ -116,7 +116,7 @@ public class FlexBuffersBuilder {
* @param bufSize size of buffer in bytes.
*/
public FlexBuffersBuilder(int bufSize) {
this(ByteBuffer.allocate(bufSize), BUILDER_FLAG_SHARE_KEYS);
this(new ArrayReadWriteBuf(bufSize), BUILDER_FLAG_SHARE_KEYS);
}
/**
@@ -132,11 +132,14 @@ public class FlexBuffersBuilder {
* @param bb `ByteBuffer` that will hold the message
* @param flags Share flags
*/
@Deprecated
public FlexBuffersBuilder(ByteBuffer bb, int flags) {
this(new ArrayReadWriteBuf(bb.array()), flags);
}
public FlexBuffersBuilder(ReadWriteBuf bb, int flags) {
this.bb = bb;
this.flags = flags;
bb.order(ByteOrder.LITTLE_ENDIAN);
bb.position(0);
}
/**
@@ -154,7 +157,7 @@ public class FlexBuffersBuilder {
*
* @return `ByteBuffer` with finished message
*/
public ByteBuffer getBuffer() {
public ReadWriteBuf getBuffer() {
assert (finished);
return bb;
}
@@ -180,17 +183,20 @@ public class FlexBuffersBuilder {
if (key == null) {
return -1;
}
int pos = bb.position();
int pos = bb.writePosition();
if ((flags & BUILDER_FLAG_SHARE_KEYS) != 0) {
if (keyPool.get(key) == null) {
bb.put(key.getBytes(StandardCharsets.UTF_8));
Integer keyFromPool = keyPool.get(key);
if (keyFromPool == null) {
byte[] keyBytes = key.getBytes(StandardCharsets.UTF_8);
bb.put(keyBytes, 0, keyBytes.length);
bb.put((byte) 0);
keyPool.put(key, pos);
} else {
pos = keyPool.get(key);
pos = keyFromPool;
}
} else {
bb.put(key.getBytes(StandardCharsets.UTF_8));
byte[] keyBytes = key.getBytes(StandardCharsets.UTF_8);
bb.put(keyBytes, 0, keyBytes.length);
bb.put((byte) 0);
keyPool.put(key, pos);
}
@@ -373,8 +379,8 @@ public class FlexBuffersBuilder {
int bitWidth = widthUInBits(blob.length);
int byteWidth = align(bitWidth);
writeInt(blob.length, byteWidth);
int sloc = bb.position();
bb.put(blob);
int sloc = bb.writePosition();
bb.put(blob, 0, blob.length);
if (trailing) {
bb.put((byte) 0);
}
@@ -384,7 +390,7 @@ public class FlexBuffersBuilder {
// Align to prepare for writing a scalar with a certain size.
private int align(int alignment) {
int byteWidth = 1 << alignment;
int padBytes = Value.paddingBytes(bb.position(), byteWidth);
int padBytes = Value.paddingBytes(bb.writePosition(), byteWidth);
while (padBytes-- != 0) {
bb.put((byte) 0);
}
@@ -463,15 +469,14 @@ public class FlexBuffersBuilder {
// some other object.
assert (stack.size() == 1);
// Write root value.
int byteWidth = align(stack.get(0).elemWidth(bb.position(), 0));
int byteWidth = align(stack.get(0).elemWidth(bb.writePosition(), 0));
writeAny(stack.get(0), byteWidth);
// Write root type.
bb.put(stack.get(0).storedPackedType());
// Write root size. Normally determined by parent, but root has no parent :)
bb.put((byte) byteWidth);
bb.limit(bb.position());
this.finished = true;
return bb;
return ByteBuffer.wrap(bb.data(), 0, bb.writePosition());
}
/*
@@ -493,13 +498,13 @@ public class FlexBuffersBuilder {
if (keys != null) {
// If this vector is part of a map, we will pre-fix an offset to the keys
// to this vector.
bitWidth = Math.max(bitWidth, keys.elemWidth(bb.position(), 0));
bitWidth = Math.max(bitWidth, keys.elemWidth(bb.writePosition(), 0));
prefixElems += 2;
}
int vectorType = FBT_KEY;
// Check bit widths and types for all elements.
for (int i = start; i < stack.size(); i++) {
int elemWidth = stack.get(i).elemWidth(bb.position(), i + prefixElems);
int elemWidth = stack.get(i).elemWidth(bb.writePosition(), i + prefixElems);
bitWidth = Math.max(bitWidth, elemWidth);
if (typed) {
if (i == start) {
@@ -528,7 +533,7 @@ public class FlexBuffersBuilder {
writeInt(length, byteWidth);
}
// Then the actual data.
int vloc = bb.position();
int vloc = bb.writePosition();
for (int i = start; i < stack.size(); i++) {
writeAny(stack.get(i), byteWidth);
}
@@ -544,7 +549,7 @@ public class FlexBuffersBuilder {
}
private void writeOffset(long val, int byteWidth) {
int reloff = (int) (bb.position() - val);
int reloff = (int) (bb.writePosition() - val);
assert (byteWidth == 8 || reloff < 1L << (byteWidth * 8));
writeInt(reloff, byteWidth);
}
@@ -610,7 +615,7 @@ public class FlexBuffersBuilder {
int prefixElems = 1;
// Check bit widths and types for all elements.
for (int i = start; i < stack.size(); i++) {
int elemWidth = Value.elemWidth(FBT_KEY, WIDTH_8, stack.get(i).key, bb.position(), i + prefixElems);
int elemWidth = Value.elemWidth(FBT_KEY, WIDTH_8, stack.get(i).key, bb.writePosition(), i + prefixElems);
bitWidth = Math.max(bitWidth, elemWidth);
}
@@ -618,7 +623,7 @@ public class FlexBuffersBuilder {
// Write vector. First the keys width/offset if available, and size.
writeInt(length, byteWidth);
// Then the actual data.
int vloc = bb.position();
int vloc = bb.writePosition();
for (int i = start; i < stack.size(); i++) {
int pos = stack.get(i).key;
assert(pos != -1);