async might work now reliably

lib/pure/asyncdispatch.nim

@@ -14,6 +14,8 @@ import os, oids, tables, strutils, macros
 import rawsockets
 export TPort
 
+#{.injectStmt: newGcInvariant().}
+
 ## AsyncDispatch
 ## -------------
 ##
@@ -130,15 +132,10 @@ when defined(windows) or defined(nimdoc):
       ioPort: THandle
       handles: TSet[TAsyncFD]
 
-    TCustomOverlapped = object
-      Internal*: DWORD
-      InternalHigh*: DWORD
-      Offset*: DWORD
-      OffsetHigh*: DWORD
-      hEvent*: THANDLE
+    TCustomOverlapped = object of TOVERLAPPED
       data*: TCompletionData
 
-    PCustomOverlapped = ptr TCustomOverlapped
+    PCustomOverlapped = ref TCustomOverlapped
 
     TAsyncFD* = distinct int
 
@@ -184,27 +181,26 @@ when defined(windows) or defined(nimdoc):
       else: timeout.int32
     var lpNumberOfBytesTransferred: DWORD
     var lpCompletionKey: ULONG
-    var lpOverlapped: POverlapped
+    var customOverlapped: PCustomOverlapped
     let res = GetQueuedCompletionStatus(p.ioPort, addr lpNumberOfBytesTransferred,
-        addr lpCompletionKey, addr lpOverlapped, llTimeout).bool
+        addr lpCompletionKey, addr customOverlapped, llTimeout).bool
 
     # http://stackoverflow.com/a/12277264/492186
     # TODO: http://www.serverframework.com/handling-multiple-pending-socket-read-and-write-operations.html
-    var customOverlapped = cast[PCustomOverlapped](lpOverlapped)
     if res:
       # This is useful for ensuring the reliability of the overlapped struct.
       assert customOverlapped.data.sock == lpCompletionKey.TAsyncFD
 
       customOverlapped.data.cb(customOverlapped.data.sock,
           lpNumberOfBytesTransferred, TOSErrorCode(-1))
-      dealloc(customOverlapped)
+      GC_unref(customOverlapped)
     else:
       let errCode = osLastError()
-      if lpOverlapped != nil:
+      if customOverlapped != nil:
         assert customOverlapped.data.sock == lpCompletionKey.TAsyncFD
         customOverlapped.data.cb(customOverlapped.data.sock,
             lpNumberOfBytesTransferred, errCode)
-        dealloc(customOverlapped)
+        GC_unref(customOverlapped)
       else:
         if errCode.int32 == WAIT_TIMEOUT:
           # Timed out
@@ -300,7 +296,8 @@ when defined(windows) or defined(nimdoc):
     while it != nil:
       # "the OVERLAPPED structure must remain valid until the I/O completes"
       # http://blogs.msdn.com/b/oldnewthing/archive/2011/02/02/10123392.aspx
-      var ol = cast[PCustomOverlapped](alloc0(sizeof(TCustomOverlapped)))
+      var ol = PCustomOverlapped()
+      GC_ref(ol)
       ol.data = TCompletionData(sock: socket, cb:
         proc (sock: TAsyncFD, bytesCount: DWord, errcode: TOSErrorCode) =
           if not retFuture.finished:
@@ -328,7 +325,7 @@ when defined(windows) or defined(nimdoc):
           success = true
           break
         else:
-          dealloc(ol)
+          GC_unref(ol)
           success = false
       it = it.ai_next
 
@@ -352,15 +349,15 @@ when defined(windows) or defined(nimdoc):
     #     '\0' in the message currently signifies a socket disconnect. Who
     #     knows what will happen when someone sends that to our socket.
     verifyPresence(socket)
-    var retFuture = newFuture[string]()
-    
+    var retFuture = newFuture[string]()    
     var dataBuf: TWSABuf
     dataBuf.buf = cast[cstring](alloc0(size))
     dataBuf.len = size
     
     var bytesReceived: DWord
     var flagsio = flags.DWord
-    var ol = cast[PCustomOverlapped](alloc0(sizeof(TCustomOverlapped)))
+    var ol = PCustomOverlapped()
+    GC_ref(ol)
     ol.data = TCompletionData(sock: socket, cb:
       proc (sock: TAsyncFD, bytesCount: DWord, errcode: TOSErrorCode) =
         if not retFuture.finished:
@@ -374,7 +371,9 @@ when defined(windows) or defined(nimdoc):
               retFuture.complete($data)
           else:
             retFuture.fail(newException(EOS, osErrorMsg(errcode)))
-        dealloc dataBuf.buf
+        if dataBuf.buf != nil:
+          dealloc dataBuf.buf
+          dataBuf.buf = nil
     )
 
     let ret = WSARecv(socket.TSocketHandle, addr dataBuf, 1, addr bytesReceived,
@@ -382,8 +381,10 @@ when defined(windows) or defined(nimdoc):
     if ret == -1:
       let err = osLastError()
       if err.int32 != ERROR_IO_PENDING:
-        dealloc dataBuf.buf
-        dealloc(ol)
+        if dataBuf.buf != nil:
+          dealloc dataBuf.buf
+          dataBuf.buf = nil
+        GC_unref(ol)
         retFuture.fail(newException(EOS, osErrorMsg(err)))
     elif ret == 0 and bytesReceived == 0 and dataBuf.buf[0] == '\0':
       # We have to ensure that the buffer is empty because WSARecv will tell
@@ -426,7 +427,8 @@ when defined(windows) or defined(nimdoc):
     dataBuf.len = data.len
 
     var bytesReceived, flags: DWord
-    var ol = cast[PCustomOverlapped](alloc0(sizeof(TCustomOverlapped)))
+    var ol = PCustomOverlapped()
+    GC_ref(ol)
     ol.data = TCompletionData(sock: socket, cb:
       proc (sock: TAsyncFD, bytesCount: DWord, errcode: TOSErrorCode) =
         if not retFuture.finished:
@@ -442,7 +444,7 @@ when defined(windows) or defined(nimdoc):
       let err = osLastError()
       if err.int32 != ERROR_IO_PENDING:
         retFuture.fail(newException(EOS, osErrorMsg(err)))
-        dealloc(ol)
+        GC_unref(ol)
     else:
       retFuture.complete()
       # We don't deallocate ``ol`` here because even though this completed
@@ -490,7 +492,8 @@ when defined(windows) or defined(nimdoc):
          client: clientSock.TAsyncFD)
       )
 
-    var ol = cast[PCustomOverlapped](alloc0(sizeof(TCustomOverlapped)))
+    var ol = PCustomOverlapped()
+    GC_ref(ol)
     ol.data = TCompletionData(sock: socket, cb:
       proc (sock: TAsyncFD, bytesCount: DWord, errcode: TOSErrorCode) =
         if not retFuture.finished:
@@ -511,7 +514,7 @@ when defined(windows) or defined(nimdoc):
       let err = osLastError()
       if err.int32 != ERROR_IO_PENDING:
         retFuture.fail(newException(EOS, osErrorMsg(err)))
-        dealloc(ol)
+        GC_unref(ol)
     else:
       completeAccept()
       # We don't deallocate ``ol`` here because even though this completed