Re: emacs-27 d66331a: Don't build the Gnulib 'utimens' module on MinGW

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Mon, 23 Mar 2020 17:52:52 +0200, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Robert Pluim <rpluim@gmail.com>
    >> Cc: Eli Zaretskii <eliz@gnu.org>
    >> Date: Mon, 23 Mar 2020 16:26:24 +0100
    >> 
    >> Apropos: we explicitly donʼt use the gnulib 'select' module, even
    >> though it looks like on MSWindows it handles both sockets and
    >> pipes. What functionality is it missing?

    Eli> SIGCHLD and C-g interrupts, I guess.  Maybe something else as well, I
    Eli> don't remember.

In that case I should go the other direction. How about the following
to remove the 1-char readahead for sockets (which then allows us to
enable datagram sockets on MSWindows).

modified   src/w32.c
@@ -8798,6 +8798,43 @@ _sys_wait_accept (int fd)
   return cp->status;
 }
 
+int
+_sys_wait_readable (int fd)
+{
+  HANDLE hEv;
+  child_process * cp;
+  int rc;
+
+  if (fd < 0 || fd >= MAXDESC)
+    return STATUS_READ_ERROR;
+
+  cp = fd_info[fd].cp;
+
+  if (cp == NULL || cp->fd != fd || cp->status != STATUS_READ_READY)
+    return STATUS_READ_ERROR;
+
+  cp->status = STATUS_READ_FAILED;
+
+  hEv = pfn_WSACreateEvent ();
+  rc = pfn_WSAEventSelect (SOCK_HANDLE (fd), hEv, FD_READ);
+  if (rc != SOCKET_ERROR)
+    {
+      do
+        {
+          rc = WaitForSingleObject (hEv, 500);
+          Sleep (5);
+        } while (rc == WAIT_TIMEOUT
+                 && cp->status != STATUS_READ_ERROR
+                 && cp->char_avail);
+      pfn_WSAEventSelect (SOCK_HANDLE (fd), NULL, 0);
+      if (rc == WAIT_OBJECT_0)
+        cp->status = STATUS_READ_SUCCEEDED;
+    }
+  pfn_WSACloseEvent (hEv);
+
+  return cp->status;
+}
+
 int
 _sys_wait_connect (int fd)
 {
@@ -8923,10 +8960,6 @@ sys_read (int fd, char * buffer, unsigned int count)
 	      return -1;
 
 	    case STATUS_READ_SUCCEEDED:
-	      /* consume read-ahead char */
-	      *buffer++ = cp->chr;
-	      count--;
-	      nchars++;
 	      cp->status = STATUS_READ_ACKNOWLEDGED;
 	      ResetEvent (cp->char_avail);
 
modified   src/w32.h
@@ -175,6 +175,7 @@ #define FILE_SERIAL             0x0800
 
 extern int _sys_read_ahead (int fd);
 extern int _sys_wait_accept (int fd);
+extern int _sys_wait_readable (int fd);
 extern int _sys_wait_connect (int fd);
 
 extern HMODULE w32_delayed_load (Lisp_Object);
modified   src/w32proc.c
@@ -1225,7 +1225,10 @@ reader_thread (void *arg)
       else if (cp->fd >= 0 && (fd_info[cp->fd].flags & FILE_LISTEN) != 0)
 	rc = _sys_wait_accept (cp->fd);
       else
-	rc = _sys_read_ahead (cp->fd);
+        if (fd_info[cp->fd].flags & FILE_SOCKET)
+          rc = _sys_wait_readable (cp->fd);
+        else
+          rc = _sys_read_ahead (cp->fd);
 
       /* Don't bother waiting for the event if we already have been
 	 told to exit by delete_child.  */