Cygwin: FIFO: introduce a new type, fifo_reader_id_t

This uniquely identifies an fhandler_fifo open for reading in any
process.

Add a new data member 'me' of this type, which is set in open, dup,
fork, and exec.

winsup/cygwin/fhandler.h

@@ -1300,6 +1300,26 @@ struct fifo_client_handler
   int pipe_state ();
 };
 
+class fhandler_fifo;
+
+struct fifo_reader_id_t
+{
+  DWORD winpid;
+  fhandler_fifo *fh;
+
+  operator bool () const { return winpid != 0 || fh != NULL; }
+
+  friend operator == (const fifo_reader_id_t &l, const fifo_reader_id_t &r)
+  {
+    return l.winpid == r.winpid && l.fh == r.fh;
+  }
+
+  friend operator != (const fifo_reader_id_t &l, const fifo_reader_id_t &r)
+  {
+    return l.winpid != r.winpid || l.fh != r.fh;
+  }
+};
+
 /* Info needed by all readers of a FIFO, stored in named shared memory. */
 class fifo_shmem_t
 {
@@ -1329,6 +1349,7 @@ class fhandler_fifo: public fhandler_base
   af_unix_spinlock_t _fifo_client_lock;
   bool reader, writer, duplexer;
   size_t max_atomic_write;
+  fifo_reader_id_t me;
 
   HANDLE shmem_handle;
   fifo_shmem_t *shmem;
@@ -1362,6 +1383,8 @@ public:
   void fifo_client_lock () { _fifo_client_lock.lock (); }
   void fifo_client_unlock () { _fifo_client_lock.unlock (); }
 
+  fifo_reader_id_t get_me () const { return me; }
+
   int open (int, mode_t);
   off_t lseek (off_t offset, int whence);
   int close ();

winsup/cygwin/fhandler_fifo.cc

@@ -65,13 +65,15 @@ STATUS_PIPE_EMPTY simply means there's no data to be read. */
 		   || _s == STATUS_PIPE_NOT_AVAILABLE \
 		   || _s == STATUS_PIPE_BUSY; })
 
+static NO_COPY fifo_reader_id_t null_fr_id = { .winpid = 0, .fh = NULL };
+
 fhandler_fifo::fhandler_fifo ():
   fhandler_base (),
   read_ready (NULL), write_ready (NULL), writer_opening (NULL),
   cancel_evt (NULL), thr_sync_evt (NULL), _maybe_eof (false), nhandlers (0),
   reader (false), writer (false), duplexer (false),
   max_atomic_write (DEFAULT_PIPEBUFSIZE),
-  shmem_handle (NULL), shmem (NULL)
+  me (null_fr_id), shmem_handle (NULL), shmem (NULL)
 {
   pipe_name_buf[0] = L'\0';
   need_fork_fixup (true);
@@ -575,6 +577,8 @@ fhandler_fifo::open (int flags, mode_t)
 	goto err_dec_nreaders;
       if (!(thr_sync_evt = create_event ()))
 	goto err_close_cancel_evt;
+      me.winpid = GetCurrentProcessId ();
+      me.fh = this;
       new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
 
       /* If we're a duplexer, we need a handle for writing. */
@@ -1119,6 +1123,7 @@ fhandler_fifo::dup (fhandler_base *child, int flags)
       if (!(fhf->thr_sync_evt = create_event ()))
 	goto err_close_cancel_evt;
       inc_nreaders ();
+      fhf->me.fh = fhf;
       new cygthread (fifo_reader_thread, fhf, "fifo_reader", fhf->thr_sync_evt);
     }
   return 0;
@@ -1164,6 +1169,7 @@ fhandler_fifo::fixup_after_fork (HANDLE parent)
       if (!(thr_sync_evt = create_event ()))
 	api_fatal ("Can't create reader thread sync event during fork, %E");
       inc_nreaders ();
+      me.winpid = GetCurrentProcessId ();
       new cygthread (fifo_reader_thread, this, "fifo_reader", thr_sync_evt);
     }
 }
@@ -1179,6 +1185,7 @@ fhandler_fifo::fixup_after_exec ()
 
       if (reopen_shmem () < 0)
 	api_fatal ("Can't reopen shared memory during exec, %E");
+      me.winpid = GetCurrentProcessId ();
       if (!(cancel_evt = create_event ()))
 	api_fatal ("Can't create reader thread cancel event during exec, %E");
       if (!(thr_sync_evt = create_event ()))