Cygwin: console: Make read() thread-safe.

- Currently read() is somehow not thread-safe. This patch fixes
  the issue.

winsup/cygwin/fhandler.h

@@ -1905,6 +1905,8 @@ class fhandler_termios: public fhandler_base
   tty_min *_tc;
   tty *get_ttyp () {return (tty *) tc ();}
   int eat_readahead (int n);
+  virtual void acquire_input_mutex_if_necessary (DWORD ms) {};
+  virtual void release_input_mutex_if_necessary (void) {};
 
  public:
   tty_min*& tc () {return _tc;}
@@ -2212,6 +2214,14 @@ private:
   void __release_input_mutex (const char *fn, int ln);
   DWORD __acquire_output_mutex (const char *fn, int ln, DWORD ms);
   void __release_output_mutex (const char *fn, int ln);
+  void acquire_input_mutex_if_necessary (DWORD ms)
+  {
+    acquire_input_mutex (ms);
+  }
+  void release_input_mutex_if_necessary (void)
+  {
+    release_input_mutex ();
+  }
 
   char *&rabuf ();
   size_t &ralen ();

winsup/cygwin/fhandler_console.cc

@@ -571,31 +571,34 @@ wait_retry:
 #define buf ((char *) pv)
 
       int ret;
-      acquire_attach_mutex (INFINITE);
       acquire_input_mutex (INFINITE);
+      acquire_attach_mutex (INFINITE);
       ret = process_input_message ();
-      release_input_mutex ();
       release_attach_mutex ();
       switch (ret)
 	{
 	case input_error:
+	  release_input_mutex ();
 	  goto err;
 	case input_processing:
+	  release_input_mutex ();
 	  continue;
 	case input_ok: /* input ready */
 	  break;
 	case input_signalled: /* signalled */
+	  release_input_mutex ();
 	  goto sig_exit;
 	case input_winch:
+	  release_input_mutex ();
 	  continue;
 	default:
 	  /* Should not come here */
+	  release_input_mutex ();
 	  goto err;
 	}
     }
 
   /* Check console read-ahead buffer filled from terminal requests */
-  acquire_input_mutex (INFINITE);
   while (con.cons_rapoi && *con.cons_rapoi && buflen)
     {
       buf[copied_chars++] = *con.cons_rapoi++;
@@ -984,9 +987,7 @@ fhandler_console::process_input_message (void)
       if (toadd)
 	{
 	  ssize_t ret;
-	  release_input_mutex ();
 	  line_edit_status res = line_edit (toadd, nread, *ti, &ret);
-	  acquire_input_mutex (INFINITE);
 	  if (res == line_edit_signalled)
 	    {
 	      stat = input_signalled;

winsup/cygwin/fhandler_termios.cc

@@ -332,7 +332,9 @@ fhandler_termios::line_edit (const char *rptr, size_t nread, termios& ti,
 
 	  termios_printf ("got interrupt %d, sending signal %d", c, sig);
 	  eat_readahead (-1);
+	  release_input_mutex_if_necessary ();
 	  tc ()->kill_pgrp (sig);
+	  acquire_input_mutex_if_necessary (INFINITE);
 	  ti.c_lflag &= ~FLUSHO;
 	  sawsig = true;
 	  goto restart_output;