finish allocate

runtime/src/main/java/org/capnproto/BuilderArena.java

@@ -61,11 +61,26 @@ public final class BuilderArena implements Arena {
             return new AllocateResult(this.segments.get(len - 1), result);
         }
 
+        // allocate_owned_memory
+
+        int size = Math.max(amount, this.nextSize);
         SegmentBuilder newSegment = new SegmentBuilder(
-            ByteBuffer.allocate(amount * Constants.BYTES_PER_WORD),
+            ByteBuffer.allocate(size * Constants.BYTES_PER_WORD),
             this);
+
+        switch (this.allocationStrategy) {
+        case GROW_HEURISTICALLY:
+            this.nextSize += size;
+            break;
+        default:
+            break;
+        }
+
+        // --------
+
         newSegment.buffer.mark();
         newSegment.buffer.order(ByteOrder.LITTLE_ENDIAN);
+        newSegment.id = len;
         this.segments.add(newSegment);
 
         return new AllocateResult(newSegment, newSegment.allocate(amount));

runtime/src/main/java/org/capnproto/FarPointer.java

@@ -0,0 +1,9 @@
+package org.capnproto;
+
+import java.nio.ByteBuffer;
+
+final class FarPointer {
+    public static void set(ByteBuffer buffer, int offset, int segmentId) {
+        buffer.putInt(8 * offset + 4, segmentId);
+    }
+}

runtime/src/main/java/org/capnproto/SegmentBuilder.java

@@ -7,6 +7,7 @@ public final class SegmentBuilder extends SegmentReader {
     public static final int FAILED_ALLOCATION = -1;
 
     public int pos = 0; // in words
+    public int id = 0;
 
     public SegmentBuilder(ByteBuffer buf, Arena arena) {
         super(buf, arena);

runtime/src/main/java/org/capnproto/WireHelpers.java

@@ -36,7 +36,20 @@ final class WireHelpers {
             int amountPlusRef = amount + Constants.POINTER_SIZE_IN_WORDS;
             BuilderArena.AllocateResult allocation = segment.getArena().allocate(amountPlusRef);
 
-            throw new Error("unimplemented");
+            //# Set up the original pointer to be a far pointer to
+            //# the new segment.
+            WirePointer.setKindAndTarget(segment.buffer, refOffset, WirePointer.FAR, allocation.offset);
+            FarPointer.set(segment.buffer, refOffset, allocation.segment.id);
+
+            //# Initialize the landing pad to indicate that the
+            //# data immediately follows the pad.
+            int resultRefOffset = allocation.offset;
+            int ptr1 = allocation.offset + Constants.POINTER_SIZE_IN_WORDS;
+
+            WirePointer.setKindAndTarget(allocation.segment.buffer, resultRefOffset, kind,
+                                         ptr1);
+
+            return new AllocateResult(ptr1, resultRefOffset, allocation.segment);
         } else {
             WirePointer.setKindAndTarget(segment.buffer, refOffset, kind, ptr);
             return new AllocateResult(ptr, refOffset, segment);