--- pty.py.orig	2008-01-30 16:49:04.325764000 -0500
+++ pty.py	2008-02-17 15:08:47.352141000 -0500
@@ -6,6 +6,16 @@
 #       UNIX Environment.  Chapter 19.
 # Author: Steen Lumholt -- with additions by Guido.
 
+# This version modified by Fergus Henderson <fergus@google.com>:
+# see pty.py.patch for the changes:
+#   - spawn() now waits for the invoked process, and returns the value
+#     returned from os.waitpid().
+#   - fixed a bug in the _copy() loop that caused it to spin using 100% CPU
+#     rather than blocking.
+# TODO(fergus): once this patch is incorporated in the upstream python
+# distribution, remove this file and use python's built-in 'pty' module
+# instead.
+
 from select import select
 import os
 import tty
@@ -136,15 +146,21 @@
     Copies
             pty master -> standard output   (master_read)
             standard input -> pty master    (stdin_read)"""
+    fds = [master_fd, STDIN_FILENO]
     while 1:
-        rfds, wfds, xfds = select(
-                [master_fd, STDIN_FILENO], [], [])
+        rfds, wfds, xfds = select(fds, [], [])
         if master_fd in rfds:
             data = master_read(master_fd)
-            os.write(STDOUT_FILENO, data)
+            if len(data) == 0: # Reached EOF.
+                fds.remove(master_fd)
+            else:
+                os.write(STDOUT_FILENO, data)
         if STDIN_FILENO in rfds:
             data = stdin_read(STDIN_FILENO)
-            _writen(master_fd, data)
+            if len(data) == 0: # Reached EOF.
+                fds.remove(STDIN_FILENO)
+            else:
+                _writen(master_fd, data)
 
 def spawn(argv, master_read=_read, stdin_read=_read):
     """Create a spawned process."""
@@ -166,3 +182,5 @@
             tty.tcsetattr(STDIN_FILENO, tty.TCSAFLUSH, mode)
 
     os.close(master_fd)
+    (_pid, status) = os.waitpid(pid, 0)
+    return status