[WIP] Copy on write optimization for buffers.

src/colony/lua/colony-node.lua

@@ -209,6 +209,7 @@ end
 
 local buffer_proto = js_obj({
   fill = function (this, value, offset, endoffset)
+    checkCopyOnWrite(this);
     local sourceBuffer = getmetatable(this).buffer
     local sourceBufferLength = getmetatable(this).bufferlen
     offset = tonumber(offset)
@@ -224,6 +225,8 @@ local buffer_proto = js_obj({
   slice = function (this, sourceStart, len)
     sourceStart = tonumber(sourceStart or 0) or 0
 
+    checkCopyOnWrite(this);
+
     if len == nil then
       len = this.length
     end
@@ -238,11 +241,14 @@ local buffer_proto = js_obj({
 
     local sourceBuffer = getmetatable(this).buffer
     local sourceBufferLength = getmetatable(this).bufferlen
-    return _of_buffer({}, tm.buffer_index(sourceBuffer, sourceStart), len - sourceStart)
+    return _of_buffer({}, tm.buffer_index(sourceBuffer, sourceStart), len - sourceStart, true)
   end,
   copy = function (this, target, targetStart, sourceStart, sourceEnd)
     local sourceBuffer = getmetatable(this).buffer
     local sourceBufferLength = getmetatable(this).bufferlen
+
+    checkCopyOnWrite(target);
+
     local targetBuffer = getmetatable(target).buffer
     local targetBufferLength = getmetatable(target).bufferlen
     if not sourceBuffer or not targetBuffer then
@@ -359,6 +365,8 @@ buffer_proto.readDoubleLE = function (this, pos, opts) return read_buf(this, pos
 buffer_proto.readDoubleBE = function (this, pos, opts) return read_buf(this, pos, opts, 8, tm.buffer_read_double, 0); end
 
 function write_buf (this, value, pos, no_assert, size, fn, le)
+  checkCopyOnWrite(this);
+
   local sourceBuffer = getmetatable(this).buffer
   local sourceBufferLength = getmetatable(this).bufferlen
   pos = tonumber(pos)
@@ -395,7 +403,8 @@ buffer_proto.writeDoubleLE = function (this, value, pos, opts) return write_buf(
 buffer_proto.writeDoubleBE = function (this, value, pos, opts) return write_buf(this, value, pos, opts, 8, tm.buffer_write_double, 0); end
 
 
-function _of_buffer (this, buf, length)
+function _of_buffer (this, buf, length, copyOnWrite)
+  this._copyOnWrite = copyOnWrite;
   setmetatable(this, {
     buffer = buf,
     bufferlen = length,
@@ -446,6 +455,17 @@ function _of_buffer (this, buf, length)
   return this
 end
 
+function checkCopyOnWrite (this)
+  if this._copyOnWrite then 
+    this._oldBuffer = getmetatable(this).buffer;
+    local bufCopy = tm.buffer_create(getmetatable(this).bufferlen)
+    tm.buffer_copy(getmetatable(this).buffer, bufCopy, 0, 0, getmetatable(this).bufferlen)
+    getmetatable(this).buffer = bufCopy;
+    this._copyOnWrite = false
+    this._newBuffer = getmetatable(this).buffer;
+  end
+end
+
 local function Buffer (this, arg, encoding)
   -- args
   local str, length = '', 0
@@ -471,7 +491,7 @@ local function Buffer (this, arg, encoding)
 
   this = {}
   local buf = tm.buffer_create(length)
-  _of_buffer(this, buf, length)
+  _of_buffer(this, buf, length, true)
 
   -- Lua internally uses a "binary" encoding, that is,
   -- operates on (1-indexable) 8-bit values.

test/suite/buffer.js

@@ -167,3 +167,27 @@ var len = buf.write('\u00bd + \u00bc = \u00be', 4);
 console.log('#', len + " bytes: " + buf.toString('utf8', 4, 4 + len));
 ok(len == 12, 'written length is 12 byes')
 ok(buf.slice(4, 4 + 12).toString() == '\u00bd + \u00bc = \u00be', 'result was written')
+
+// copy on write -> write(type)(size) tests
+var writableFunctions = ["writeUInt8", "writeUInt16LE", "writeUInt16BE", "writeUInt32LE", "writeUInt32BE", "writeInt8", 
+													"writeInt16LE", "writeInt16BE", "writeInt32LE", "writeInt32BE", "writeFloatLE", "writeFloatBE", 
+													"writeDoubleLE", "writeDoubleBE"];
+for (var i = 0; i<writableFunctions.length; i++) {
+	var buf = new Buffer(256);
+	buf[writableFunctions[i]](0x55, 0)
+	console.log("old buf:", buf._oldBuffer, "new buf:", buf._newBuffer)
+	ok(buf._oldBuffer !== buf._newBuffer, "New buffer pointer is different than old buffer pointer");
+}
+
+
+// copy on write -> other copy and slice
+var buf = new Buffer(256);
+buf.slice(0, 10);
+console.log("old buf:", buf._oldBuffer, "new buf:", buf._newBuffer)
+ok(buf._oldBuffer !== buf._newBuffer, "New buffer pointer is different than old buffer pointer");
+
+var buf = new Buffer(256);
+var buf2 = new Buffer(256);
+buf.copy(buf2, 0, 0, buf.length);
+console.log("old buf:", buf2._oldBuffer, "new buf:", buf2._newBuffer)
+ok(buf2._oldBuffer !== buf2._newBuffer, "New buffer pointer is different than old buffer pointer");