From 70e60d969c4006ddce3a4e16549d0271158ba8f4 Mon Sep 17 00:00:00 2001
From: Ken Brown <kbrown@cornell.edu>
Date: Thu, 17 Jan 2019 16:55:20 -0500
Subject: [PATCH FIFO, draft 4/4] Cygwin: fhandler_fifo: add a spinlock

Don't let listen_client_thread and raw_read access the pipe_instance
list simultaneously.
---
 winsup/cygwin/fhandler.h       |  3 +++
 winsup/cygwin/fhandler_fifo.cc | 27 +++++++++++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index 311cf0958..a557375f5 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -1249,6 +1249,7 @@ class fhandler_fifo: public fhandler_base_overlapped
   HANDLE lct_termination_evt;
   pipe_instance inst[MAX_INSTANCES];
   int ninstances, nconnected;
+  af_unix_spinlock_t _pipe_inst_lock;
   bool __reg2 wait (HANDLE);
   char __reg2 *fifo_name (char *, const char *);
   int disconnect_and_reconnect (int);
@@ -1258,6 +1259,8 @@ class fhandler_fifo: public fhandler_base_overlapped
 public:
   fhandler_fifo ();
   DWORD listen_client_thread ();
+  void pipe_inst_lock () { _pipe_inst_lock.lock (); }
+  void pipe_inst_unlock () { _pipe_inst_lock.unlock (); }
   int open (int, mode_t);
   off_t lseek (off_t offset, int whence);
   int close ();
diff --git a/winsup/cygwin/fhandler_fifo.cc b/winsup/cygwin/fhandler_fifo.cc
index 5bc64408b..452978202 100644
--- a/winsup/cygwin/fhandler_fifo.cc
+++ b/winsup/cygwin/fhandler_fifo.cc
@@ -213,8 +213,12 @@ fhandler_fifo::listen_client_thread ()
 {
   while (1)
     {
+      pipe_inst_lock ();
       if (nconnected == ninstances && create_pipe_instance () < 0)
-	return -1;
+	{
+	  pipe_inst_unlock ();
+	  return -1;
+	}
 
       /* Wait for a client to connect. */
       HANDLE w[MAX_INSTANCES + 1];
@@ -224,6 +228,7 @@ fhandler_fifo::listen_client_thread ()
 	w[i] = inst[i].connected ? inst[i].dummy_evt
 	  : inst[i].fh->get_overlapped ()->hEvent;
       w[ninstances] = lct_termination_evt;
+      pipe_inst_unlock ();
       if (!arm (read_ready))
 	goto errout;
       wait_ret = WaitForMultipleObjects (ninstances + 1, w, false, INFINITE);
@@ -234,8 +239,11 @@ fhandler_fifo::listen_client_thread ()
 	return 0;
       else
 	{
+	  pipe_inst_lock ();
 	  inst[i].connected = true;
 	  nconnected++;
+	  pipe_inst_unlock ();
+	  yield ();
 	}
     }
 errout:
@@ -497,6 +505,7 @@ fhandler_fifo::raw_read (void *in_ptr, size_t& len)
       if (!check_listen_client_thread ())
 	goto errout;
 
+      pipe_inst_lock ();
       for (int i = 0; i < ninstances; i++)
 	if (inst[i].connected)
 	  {
@@ -508,12 +517,22 @@ fhandler_fifo::raw_read (void *in_ptr, size_t& len)
 	    inst[i].fh->set_nonblocking (was_nonblocking);
 	    nread = (ssize_t) len;
 	    if (nread > 0)
-	      return;
+	      {
+		pipe_inst_unlock ();
+		return;
+	      }
 	    else if (nread < 0 && errno != EAGAIN)
-	      goto errout;
+	      {
+		pipe_inst_unlock ();
+		goto errout;
+	      }
 	    else if (nread == 0 && disconnect_and_reconnect (i) < 0)
-	      goto errout;
+	      {
+		pipe_inst_unlock ();
+		goto errout;
+	      }
 	  }
+      pipe_inst_unlock ();
       if (is_nonblocking ())
 	{
 	  set_errno (EAGAIN);
-- 
2.17.0