smalloc: check if object has external memory

Add HasExternalData API to check if Object has externally allocated
memory, and accompanying tests.

doc/api/smalloc.markdown

@@ -2,11 +2,14 @@
 
     Stability: 1 - Experimental
 
+`Smalloc` is a light weight API that allows developers to attach external data
+to arbitrary `Object`s.
+
 ## smalloc.alloc(length[, receiver][, type])
 
-* `length` {Number} `<= smalloc.kMaxLength`
-* `receiver` {Object}, Optional, Default: `new Object`
-* `type` {Enum}, Optional, Default: `Uint8`
+* `length` {Number} `<= kMaxLength` (maximum allowed Buffer size by v8)
+* `receiver` {Object} Optional, Default: `new Object()`
+* `type` {Enum} Optional, Default: `Uint8`
 
 Returns `receiver` with allocated external array data. If no `receiver` is
 passed then a new Object will be created and returned.
@@ -46,13 +49,13 @@ possible options are listed in `smalloc.Types`. Example usage:
 
     // { '0': 0, '1': 0.1, '2': 0.2 }
 
-## smalloc.copyOnto(source, sourceStart, dest, destStart, copyLength);
+## smalloc.copyOnto(source, sourceStart, dest, destStart, copyLength)
 
-* `source` Object with external array allocation
-* `sourceStart` Position to begin copying from
-* `dest` Object with external array allocation
-* `destStart` Position to begin copying onto
-* `copyLength` Length of copy
+* `source` {Object} with external array allocation
+* `sourceStart` {Position} to begin copying from
+* `dest` {Object} with external array allocation
+* `destStart` {Position} to begin copying onto
+* `copyLength` {Length} of copy
 
 Copy memory from one external array allocation to another. No arguments are
 optional, and any violation will throw.
@@ -77,7 +80,7 @@ need to set any additional properties for this to work.
 
 ## smalloc.dispose(obj)
 
-* `obj` Object
+* `obj` {Object}
 
 Free memory that has been allocated to an object via `smalloc.alloc`.
 
@@ -107,6 +110,12 @@ careful. Cryptic errors may arise in applications that are difficult to trace.
 
 `dispose()` does not support Buffers, and will throw if passed.
 
+## smalloc.hasExternalData(obj)
+
+* `obj` {Object}
+
+Returns `true` if the `obj` has externally allocated memory.
+
 ## smalloc.kMaxLength
 
 Size of maximum allocation. This is also applicable to Buffer creation.

lib/smalloc.js

@@ -26,6 +26,7 @@ var util = require('util');
 exports.alloc = alloc;
 exports.copyOnto = smalloc.copyOnto;
 exports.dispose = dispose;
+exports.hasExternalData = smalloc.hasExternalData;
 
 // don't allow kMaxLength to accidentally be overwritten. it's a lot less
 // apparent when a primitive is accidentally changed.

src/smalloc.cc

@@ -23,6 +23,7 @@
 
 #include "env.h"
 #include "env-inl.h"
+#include "node.h"
 #include "node_internals.h"
 #include "v8-profiler.h"
 #include "v8.h"
@@ -402,6 +403,17 @@ void TargetFreeCallback(Isolate* isolate,
 }
 
 
+void HasExternalData(const FunctionCallbackInfo<Value>& args) {
+  args.GetReturnValue().Set(args[0]->IsObject() &&
+                            HasExternalData(args[0].As<Object>()));
+}
+
+
+bool HasExternalData(Local<Object> obj) {
+  return obj->HasIndexedPropertiesInExternalArrayData();
+}
+
+
 class RetainedAllocInfo: public RetainedObjectInfo {
  public:
   explicit RetainedAllocInfo(Handle<Value> wrapper);
@@ -471,6 +483,8 @@ void Initialize(Handle<Object> exports,
   NODE_SET_METHOD(exports, "alloc", Alloc);
   NODE_SET_METHOD(exports, "dispose", AllocDispose);
 
+  NODE_SET_METHOD(exports, "hasExternalData", HasExternalData);
+
   exports->Set(FIXED_ONE_BYTE_STRING(node_isolate, "kMaxLength"),
                Uint32::NewFromUnsigned(kMaxLength, env->isolate()));
 

src/smalloc.h

@@ -101,6 +101,12 @@ NODE_EXTERN void Alloc(v8::Handle<v8::Object> obj,
  */
 NODE_EXTERN void AllocDispose(v8::Handle<v8::Object> obj);
 
+
+/**
+ * Check if the Object has externally allocated memory.
+ */
+NODE_EXTERN bool HasExternalData(v8::Local<v8::Object> obj);
+
 }  // namespace smalloc
 }  // namespace node
 

test/simple/test-smalloc.js

@@ -156,6 +156,25 @@ copyOnto(c, 0, b, 0, 2);
 assert.equal(b[0], 0.1);
 
 
+// verify checking external if has external memory
+
+// check objects
+var b = {};
+assert.ok(!smalloc.hasExternalData(b));
+alloc(1, b);
+assert.ok(smalloc.hasExternalData(b));
+var f = function() { };
+alloc(1, f);
+assert.ok(smalloc.hasExternalData(f));
+
+// and non-objects
+assert.ok(!smalloc.hasExternalData(true));
+assert.ok(!smalloc.hasExternalData(1));
+assert.ok(!smalloc.hasExternalData('string'));
+assert.ok(!smalloc.hasExternalData(null));
+assert.ok(!smalloc.hasExternalData());
+
+
 // verify alloc throws properly
 
 // arrays are not supported