* dtable.cc (dtable::find_fifo): Release lock after fifo found (still racy).

* fhandler.h (fhandler_fifo::get_io_handle): New fifo-specific method.
* fhandler_fifo.cc (fhandler_fifo::close): Close output_handle only if it is
open.
(fhandler_fifo::open_not_mine): Reorganize slightly.  Don't call _pinfo methods
when the fifo is owned by me or suffer dtable lock_cs deadlock.
(fhandler_fifo::open): Call open_not_mine first, otherwise open myself
(racy).
* pinfo.cc (_pinfo::commune_recv): Duplicate fifo handles here in requesting
processes arena to avoid one potential race (of many).
(_pinfo::commune_send): Move all PICOM_FIFO code under one case statement.
* thread.cc (pthread::init_mainthread) Use existing hMainProc handle rather
than calling GetCurrentProcess.

winsup/cygwin/fhandler.h

@@ -324,6 +324,7 @@ class fhandler_base
   bool is_fs_special () {return pc.is_fs_special ();}
   bool device_access_denied (int) __attribute__ ((regparm (2)));
   int fhaccess (int flags) __attribute__ ((regparm (2)));
+  friend class fhandler_fifo;
 };
 
 class fhandler_socket: public fhandler_base
@@ -454,6 +455,7 @@ class fhandler_fifo: public fhandler_pipe
   HANDLE owner;		// You can't have too many mutexes, now, can you?
   long read_use;
   long write_use;
+  virtual HANDLE& get_io_handle () { return io_handle ?: output_handle; }
 public:
   fhandler_fifo ();
   int open (int flags, mode_t mode = 0);