Expose transferable constructor to Int8List

runtime/lib/byte_array.cc

Index: runtime/lib/byte_array.cc
diff --git a/runtime/lib/byte_array.cc b/runtime/lib/byte_array.cc
index 2f61030e7a0b75145873cab828df04bebaf4c3d1..19b99954844d30882ece7015aac26ae8ea1ae1a7 100644
--- a/runtime/lib/byte_array.cc
+++ b/runtime/lib/byte_array.cc
@@ -42,6 +42,32 @@ static void LengthCheck(intptr_t len, intptr_t max) {
   }
 }
 
+// Allocates an aligned region of len bytes from the C heap.
+static void* AllocateExternalBytes(intptr_t len, intptr_t alignment = 16) {

[cshapiro, 2012/11/28 22:28:01]

Maybe stick this constant into the base class of the external byte arrays.

+  intptr_t pointersize = sizeof(len);
+  intptr_t slop = alignment+pointersize;

[srdjan, 2012/11/28 23:30:26]

please add spaces around +, - and everywhere else in new code.

+  void* bytes = malloc(len+slop);

[srdjan, 2012/11/28 23:30:26]

why not intptr_t* ptr = reinterpret_cast<intptr_t*>(malloc(...)), getting rid of
"bytes* void"? Why is ptr intptr_t instead of intptr_t* ?

+  intptr_t ptr = reinterpret_cast<intptr_t>(bytes);
+  // Move forward and then round down to the alignment boundary.
+  ptr += slop;
+  ptr &= (alignment-1);
+  // Store the original address immediately before the address we return.
+  intptr_t* address_slot = reinterpret_cast<intptr_t*>(ptr-pointersize);
+  *address_slot = reinterpret_cast<intptr_t>(bytes);
+  return reinterpret_cast<void*>(ptr);
+}
+
+// Free an aligned region of memory
+// that was allocated by AllocateExternalBytes.
+// Called as a Dart_PeerFinalizer callback.
+static void FinalizeExternalBytes(void* bytes) {
+  intptr_t pointersize = sizeof(bytes);
+  intptr_t ptr = reinterpret_cast<intptr_t>(bytes);

[srdjan, 2012/11/28 23:30:26]

ditto

+  intptr_t* address_slot = reinterpret_cast<intptr_t*>(ptr-pointersize);
+  void* bytes = reinterpret_cast<void*>(*address_slot);
+  free(bytes);
+}
+
 
 #define GETTER_ARGUMENTS(ArrayT, ValueT)                                \
   GET_NATIVE_ARGUMENT(ArrayT, array, arguments->NativeArgAt(0));        \
@@ -285,6 +311,18 @@ DEFINE_NATIVE_ENTRY(Int8Array_new, 1) {
 }
 
 
+DEFINE_NATIVE_ENTRY(Int8Array_newTransferrable, 1) {
+  GET_NATIVE_ARGUMENT(Smi, length, arguments->NativeArgAt(0));
+  intptr_t len = length.Value();
+  LengthCheck(len, Int8Array::kMaxElements);
+  void* bytes = AllocateExternalBytes(len);
+  return ExternalInt8Array::New(reinterpret_cast<int8_t*>(bytes),
+                                len,
+                                bytes,
+                                FinalizeExternalBytes);
+}
+
+
 DEFINE_NATIVE_ENTRY(Int8Array_getIndexed, 2) {
   GETTER(Int8Array, Smi, int8_t);
 }