Refactor exceptions in __pty_make_controlling_tty

Make very clear which exceptions we expect, where, and why.

I've done exaustive testing from within cron(1) and without.
I've been unable to reproduce the previously discovered
os.ttyname issue, so that exception handling loop has been removed.

Also, resolves the ENXIO reference (thanks TK!). Pushing to
test this on OSX and later cygwin with the non_native pty fork test

1 files changed, 17 insertions, 39 deletions

diff --git a/pexpect/__init__.py b/pexpect/__init__.py
index 1442aa8..a468667 100644
--- a/pexpect/__init__.py
+++ b/pexpect/__init__.py
@@ -719,59 +719,37 @@ class spawn(object):
         more portable than the pty.fork() function. Specifically, this should
         work on Solaris. '''
 
-        # os.ttyname() fails for the child process under a rare timing
-        # condition (about 1 in 10 on SmartOs in a VMWare machine). May
-        # raise OSError as errno ENOTTY -- ptsname(3C) should be used,
-        # on this system, but python does not expose it, it would require
-        # ctypes + libc. which is also not available, filed patch as
-        # http://bugs.python.org/issue20664
-        child_name, tries = None, 0
-        _poll, _max_tries= 0.1, 10
-        while child_name is None:
-            try:
-                child_name = os.ttyname(tty_fd)
-                break
-            except OSError:
-                tries += 1
-                if tries > _max_tries:
-                    raise
-                time.sleep(_poll)
+        child_name = os.ttyname(tty_fd)
 
-        # Disconnect from controlling tty. Harmless if not already connected.
+        # Disconnect from controlling tty, if any.  Raises OSError of ENXIO
+        # if there was no controlling tty to begin with, such as when
+        # executed by a cron(1) job.
         try:
             fd = os.open("/dev/tty", os.O_RDWR | os.O_NOCTTY)
             os.close(fd)
-        except OSError:
-            # Already disconnected. This happens if running inside cron.
-            pass
+        except OSError, err:
+            if err.errno != errno.ENXIO:
+                raise
 
         os.setsid()
 
-        # Verify we are disconnected from controlling tty
-        # by attempting to open it again.
+        # Verify we are disconnected from controlling tty by attempting to open
+        # it again.  We expect that OSError of ENXIO should always be raised.
         try:
             fd = os.open("/dev/tty", os.O_RDWR | os.O_NOCTTY)
             os.close(fd)
-        except OSError:
-            # Good! We are disconnected from a controlling tty.
-            pass
+            raise ExceptionPexpect("OSError of errno.ENXIO should be raised.")
+        except OSError, err:
+            if err.errno != errno.ENXIO:
+                raise
 
         # Verify we can open child pty.
         fd = os.open(child_name, os.O_RDWR)
-        if fd < 0:
-            raise ExceptionPexpect("Could not open child pty, " + child_name)
-        else:
-            os.close(fd)
+        os.close(fd)
 
         # Verify we now have a controlling tty.
-        try:
-            fd = os.open("/dev/tty", os.O_WRONLY)
-            os.close(fd)
-        except OSError as err:
-            if err.args[0] == ENXIO:
-                # on Solaris, `/dev/tty' raises OSError upon opening, though
-                # it does exist: /dev/tty -> ../devices/pseudo/sy@0:tty
-                pass
+        fd = os.open("/dev/tty", os.O_WRONLY)
+        os.close(fd)
 
 
     def fileno(self):
@@ -2141,4 +2119,4 @@ def split_command_line(command_line):
         arg_list.append(arg)
     return arg_list
 
-# vi:set sr et ts=4 sw=4 ft=python :
+# vim: set shiftround expandtab tabstop=4 shiftwidth=4 ft=python autoindent :