ARC: default to a shared heap with --threads:on

lib/system/allocators.nim

@@ -46,18 +46,24 @@ proc getLocalAllocator*(): Allocator =
         result = c_malloc(cuint size)
         # XXX do we need this?
         nimZeroMem(result, size)
+      elif compileOption("threads"):
+        result = system.allocShared0(size)
       else:
         result = system.alloc0(size)
       inc a.allocCount
     result.dealloc = proc (a: Allocator; p: pointer; size: int) {.nimcall, raises: [].} =
       when defined(useMalloc) and not defined(nimscript):
         c_free(p)
+      elif compileOption("threads"):
+        system.deallocShared(p)
       else:
         system.dealloc(p)
       inc a.deallocCount
     result.realloc = proc (a: Allocator; p: pointer; oldSize, newSize: int): pointer {.nimcall, raises: [].} =
       when defined(useMalloc) and not defined(nimscript):
         result = c_realloc(p, cuint newSize)
+      elif compileOption("threads"):
+        result = system.reallocShared(p, newSize)
       else:
         result = system.realloc(p, newSize)
       nimZeroMem(result +! oldSize, newSize - oldSize)

lib/system/refs_v2.nim

@@ -67,6 +67,8 @@ proc nimNewObj(size: int): pointer {.compilerRtl.} =
     var orig = c_malloc(cuint s)
     nimZeroMem(orig, s)
     result = orig +! sizeof(RefHeader)
+  elif compileOption("threads"):
+    result = allocShared0(s) +! sizeof(RefHeader)
   else:
     result = alloc0(s) +! sizeof(RefHeader)
   when hasThreadSupport:
@@ -93,6 +95,8 @@ proc nimRawDispose(p: pointer) {.compilerRtl.} =
         quit 1
     when defined(useMalloc):
       c_free(p -! sizeof(RefHeader))
+    elif compileOption("threads"):
+      deallocShared(p -! sizeof(RefHeader))
     else:
       dealloc(p -! sizeof(RefHeader))
     if allocs > 0: