[python-sybase] This routine cannot be called because another command structure has results pending

[Greg W. <gwa...@py...>]

Back in May 2002, Ralph Heinkel reported a mysterious error, "This
routine cannot be called because another command structure has results
pending".  Here's his post:

  http://www.object-craft.com.au/pipermail/python-sybase/2002-May/000034.html

He posted a test program that reproduces the problem, and it still
reproduces perfectly for me.  It appears that any error on a connection
renders that connection unusable, or at least un-commit()able and
un-rollback()able.  I'm connecting to Sybase ASE 11.0.3.3 (using
libct.so and libcs.so supplied with the Sybase engine) and python-sybase
0.37.

Here's my slight variation on Ralph's test program:

-- syberror ------------------------------------------------------------
#!/usr/bin/python

# Attempt to reproduce the mysterious "This routine cannot be called
# because another command structure has results pending." error.
#
# Based on code seen in this mailing list post:
#   http://www.object-craft.com.au/pipermail/python-sybase/2002-May/000034.html

import sys
import Sybase
Sybase._ctx.debug = 1

args = sys.argv[1:]
if len(args) != 3:
    sys.exit("usage: syberror server username password")

(server, username, password) = args
db = Sybase.connect(server, username, password)
print "successfully connected to %s" % server
cur = db.cursor()
try:
    # produce an error - THE TABLE 'DUMMY' DOES NOT EXIST
    cur.execute('select * from dummy')
    print "WTF?!?  select should have failed!"
except Sybase.Error, err:
    print "select failed as expected: %s" % err

cur.close()
db.commit()
------------------------------------------------------------------------

The most important change is that I added "_ctx.debug = 1", as requested
by Dave Cole in a followup.

And here is the output I get from running this program (username and
password censored):

------------------------------------------------------------------------
ct_con_alloc(ctx0, &conn) -> CS_SUCCEED, conn0
ct_con_props(conn0, CS_SET, CS_USERNAME, "***", CS_NULLTERM, NULL) -> CS_SUCCEEDct_con_props(conn0, CS_SET, CS_PASSWORD, "********", CS_NULLTERM, NULL) -> CS_SUCCEED
servermsg_cb
ct_connect(conn0, "MIRA321", CS_NULLTERM) -> CS_SUCCEED
ct_options(conn0, CS_SET, CS_OPT_CHAINXACTS, 1, CS_UNUSED, NULL) -> CS_SUCCEED
successfully connected to MIRA321
Cursor.execute
_lock: count -> 1
ct_cmd_alloc(conn0, &cmd) -> CS_SUCCEED, cmd0
_lock: count -> 2
_set_state: _LAZY_IDLE
_unlock: count -> 1
ct_command(cmd0, CS_LANG_CMD, "select * from dummy", CS_NULLTERM, CS_UNUSED) -> CS_SUCCEED
_set_state: _LAZY_FETCHING
ct_send(cmd0) -> CS_SUCCEED
_start_results
servermsg_cb
Msg 156, Level 15, State 1, Line 1
Incorrect syntax near the keyword 'dummy'.
ct_results(cmd0, &result) -> CS_SUCCEED, CS_CMD_FAIL
select failed as expected: Msg 156, Level 15, State 1, Line 1
Incorrect syntax near the keyword 'dummy'.

ct_cmd_alloc(conn0, &cmd) -> CS_SUCCEED, cmd1
ct_command(cmd1, CS_LANG_CMD, "commit transaction", CS_NULLTERM, CS_UNUSED) -> CS_SUCCEED
clientmsg_cb
Layer: 1, Origin: 1
ct_send(): user api layer: external error: This routine cannot be called because another command structure has results pending.ct_send(cmd1) -> CS_FAIL
ct_cancel(conn0, NULL, CS_CANCEL_ALL) -> CS_SUCCEED
_unlock: count -> 0
ct_cmd_drop(cmd0) -> CS_SUCCEED
Traceback (most recent call last):
  File "./syberror", line 30, in ?
    db.commit()
  File "/usr/local/Intelerad/3rd_Party/python/lib/python2.3/site-packages/Sybase.py", line 971, in commit
    self.execute('commit transaction')
  File "/usr/local/Intelerad/3rd_Party/python/lib/python2.3/site-packages/Sybase.py", line 996, in execute
    fetcher.start(self.arraysize)
  File "/usr/local/Intelerad/3rd_Party/python/lib/python2.3/site-packages/Sybase.py", line 307, in start
    status = self._cmd.ct_send()
  File "/usr/local/Intelerad/3rd_Party/python/lib/python2.3/site-packages/Sybase.py", line 184, in _clientmsg_cb
    raise DatabaseError(_fmt_client(msg))
Sybase.DatabaseError: Layer: 1, Origin: 1
ct_send(): user api layer: external error: This routine cannot be called because another command structure has results pending.
ct_cmd_drop(cmd1) -> CS_SUCCEED
ct_con_props(conn0, CS_GET, CS_CON_STATUS, &value, CS_UNUSED, NULL) -> CS_SUCCEED, CS_CONSTAT_CONNECTED
ct_close(conn0, CS_FORCE_CLOSE) -> CS_SUCCEED
ct_con_drop(conn0) -> CS_SUCCEED
------------------------------------------------------------------------

Does anyone understand what's going on here?  For the longest time, I
have assumed this was a subtle bug in my code, but now that I have this
simple test script I really doubt that.  How can one error make it
impossible to commit() or rollback() the current transaction?  (Same
result if the last line is db.rollback(), by the way.)  Is this a bug in
python-sybase?  or in ctlib?  or elsewhere?

Thanks --

        Greg