Ensure BoundingBoxEvent hooks stay synchronised

Multi-threading issues may have caused the NPEs in getBB.

Author: LeafHacker

src/main/java/clientapi/load/mixin/MixinBlock.java

@@ -55,19 +55,23 @@ private void canCollideCheck(IBlockState state, boolean hitIfLiquid, CallbackInf
 
     @Inject(method = "addCollisionBoxToList(Lnet/minecraft/block/state/IBlockState;Lnet/minecraft/world/World;Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/util/math/AxisAlignedBB;Ljava/util/List;Lnet/minecraft/entity/Entity;Z)V",
             at = @At("HEAD"))
-    private void in(IBlockState state, World world, BlockPos pos, AxisAlignedBB entityBox, List<AxisAlignedBB> collidingBoxes, @Nullable Entity entity, boolean isActualState, CallbackInfo ci) {
-        Block block = (Block) (Object) (this);
-        bbEvent = new BoundingBoxEvent(block, pos, block.getCollisionBoundingBox(state, world, pos), collidingBoxes, entity);
-        ClientAPI.EVENT_BUS.post(bbEvent);
+    private void addCollisionBox(IBlockState state, World world, BlockPos pos, AxisAlignedBB entityBox, List<AxisAlignedBB> collidingBoxes, @Nullable Entity entity, boolean isActualState, CallbackInfo ci) {
+        synchronized (this) {
+            Block block = (Block) (Object) (this);
+            bbEvent = new BoundingBoxEvent(block, pos, block.getCollisionBoundingBox(state, world, pos), collidingBoxes, entity);
+            ClientAPI.EVENT_BUS.post(bbEvent);
+        }
     }
 
     @Redirect(method = "addCollisionBoxToList(Lnet/minecraft/block/state/IBlockState;Lnet/minecraft/world/World;Lnet/minecraft/util/math/BlockPos;Lnet/minecraft/util/math/AxisAlignedBB;Ljava/util/List;Lnet/minecraft/entity/Entity;Z)V",
             at = @At(value = "INVOKE", target = "Lnet/minecraft/block/state/IBlockState;getCollisionBoundingBox(Lnet/minecraft/world/IBlockAccess;Lnet/minecraft/util/math/BlockPos;)Lnet/minecraft/util/math/AxisAlignedBB;"))
     private AxisAlignedBB getBB(IBlockState state, IBlockAccess world, BlockPos pos) {
-        AxisAlignedBB bb = (bbEvent == null) ?
-                state.getCollisionBoundingBox(world, pos):
-                bbEvent.getBoundingBox();
-        bbEvent = null;
-        return bb;
+        synchronized (this) {
+            AxisAlignedBB bb = (bbEvent == null) ?
+                    state.getCollisionBoundingBox(world, pos) :
+                    bbEvent.getBoundingBox();
+            bbEvent = null;
+            return bb;
+        }
     }
 }