smalloc: add api to manually dispose Persistent

If the user knows the allocation is no longer needed then the memory can
be manually released.

Currently this will not ClearWeak the Persistent, so the callback will
still run.

If the user passed a ClearWeak callback, and then disposed the object,
the buffer callback argument will == NULL.

src/smalloc.cc

@@ -173,6 +173,27 @@ void TargetCallback(Isolate* isolate, Persistent<Object>* target, char* data) {
 }
 
 
+Handle<Value> AllocDispose(const Arguments& args) {
+  AllocDispose(args[0]->ToObject());
+  return Undefined(node_isolate);
+}
+
+
+void AllocDispose(Handle<Object> obj) {
+  char* data = static_cast<char*>(obj->GetIndexedPropertiesExternalArrayData());
+  size_t length = obj->GetIndexedPropertiesExternalArrayDataLength();
+
+  if (data == NULL || length == 0)
+    return;
+
+  obj->SetIndexedPropertiesToExternalArrayData(NULL,
+                                               kExternalUnsignedByteArray,
+                                               0);
+  delete[] data;
+  node_isolate->AdjustAmountOfExternalAllocatedMemory(-length);
+}
+
+
 void Alloc(Handle<Object> obj, size_t length, FreeCallback fn, void* hint) {
   assert(length <= kMaxLength);
 
@@ -286,6 +307,8 @@ void Initialize(Handle<Object> exports) {
 
   exports->Set(String::New("alloc"),
                FunctionTemplate::New(Alloc)->GetFunction());
+  exports->Set(String::New("dispose"),
+               FunctionTemplate::New(AllocDispose)->GetFunction());
 
   exports->Set(String::New("kMaxLength"),
                Uint32::New(kMaxLength, node_isolate));

src/smalloc.h

@@ -56,6 +56,12 @@ void Alloc(v8::Handle<v8::Object> obj,
            FreeCallback fn,
            void* hint);
 
+/**
+ * Free memory associated with an externally allocated object. If no external
+ * memory is allocated to the object then nothing will happen.
+ */
+void AllocDispose(v8::Handle<v8::Object> obj);
+
 }  // namespace smalloc
 
 }  // namespace node

test/simple/test-smalloc-dispose-segfault.js

@@ -0,0 +1,50 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+
+var spawn = require('child_process').spawn;
+var smalloc = process.binding('smalloc');
+var alloc = smalloc.alloc;
+var dispose = smalloc.dispose;
+
+
+// child
+if (process.argv[2] === 'child') {
+
+  // test that disposing an allocation won't cause the MakeWeakCallback to try
+  // and free invalid memory
+  for (var i = 0; i < 1e4; i++) {
+    dispose(alloc({}, 5));
+    if (i % 10 === 0) gc();
+  }
+
+} else {
+  // test case
+  var child = spawn(process.execPath,
+                ['--expose_gc', __filename, 'child']);
+
+  child.on('exit', function(code, signal) {
+    assert.equal(code, 0, signal);
+    console.log('dispose didn\'t segfault');
+  });
+}

test/simple/test-smalloc.js

@@ -25,6 +25,7 @@ var assert = require('assert');
 var smalloc = process.binding('smalloc');
 var alloc = smalloc.alloc;
 var copyOnto = smalloc.copyOnto;
+var dispose = smalloc.dispose;
 var sliceOnto = smalloc.sliceOnto;
 
 
@@ -87,3 +88,11 @@ for (var i = 0; i < 6; i++) {
   assert.equal(c[i], i);
   assert.equal(c[i + 6], i * 2);
 }
+
+
+// test disposal
+
+var b = alloc({}, 5);
+dispose(b);
+for (var i = 0; i < 5; i++)
+  assert.equal(b[i], undefined);