"""Drop-in replacement for the thread module.

Meant to be used as a brain-dead substitute so that threaded code does
not need to be rewritten for when the thread module is not present.

Suggested usage is::

try:
import thread
except ImportError:
import dummy_thread as thread

"""
# Exports only things specified by thread documentation;
# skipping obsolete synonyms allocate(), start_new(), exit_thread().
__all__ = ['error', 'start_new_thread', 'exit', 'get_ident', 'allocate_lock',
'interrupt_main', 'LockType']

import traceback as _traceback

class error(Exception):
"""Dummy implementation of thread.error."""

def __init__(self, *args):
self.args = args

def start_new_thread(function, args, kwargs={}):
"""Dummy implementation of thread.start_new_thread().

Compatibility is maintained by making sure that ``args`` is a
tuple and ``kwargs`` is a dictionary. If an exception is raised
and it is SystemExit (which can be done by thread.exit()) it is
caught and nothing is done; all other exceptions are printed out
by using traceback.print_exc().

If the executed function calls interrupt_main the KeyboardInterrupt will be
raised when the function returns.

"""
if type(args) != type(tuple()):
raise TypeError("2nd arg must be a tuple")
if type(kwargs) != type(dict()):
raise TypeError("3rd arg must be a dict")
global _main
_main = False
try:
function(*args, **kwargs)
except SystemExit:
pass
except:
_traceback.print_exc()
_main = True
global _interrupt
if _interrupt:
_interrupt = False
raise KeyboardInterrupt

def exit():
"""Dummy implementation of thread.exit()."""
raise SystemExit

def get_ident():
"""Dummy implementation of thread.get_ident().

Since this module should only be used when threadmodule is not
available, it is safe to assume that the current process is the
only thread. Thus a constant can be safely returned.
"""
return -1

def allocate_lock():
"""Dummy implementation of thread.allocate_lock()."""
return LockType()

def stack_size(size=None):
"""Dummy implementation of thread.stack_size()."""
if size is not None:
raise error("setting thread stack size not supported")
return 0

class LockType(object):
"""Class implementing dummy implementation of thread.LockType.

Compatibility is maintained by maintaining self.locked_status
which is a boolean that stores the state of the lock. Pickling of
the lock, though, should not be done since if the thread module is
then used with an unpickled ``lock()`` from here problems could
occur from this class not having atomic methods.

"""

def __init__(self):
self.locked_status = False

def acquire(self, waitflag=None):
"""Dummy implementation of acquire().

For blocking calls, self.locked_status is automatically set to
True and returned appropriately based on value of
``waitflag``. If it is non-blocking, then the value is
actually checked and not set if it is already acquired. This
is all done so that threading.Condition's assert statements
aren't triggered and throw a little fit.

"""
if waitflag is None or waitflag:
self.locked_status = True
return True
else:
if not self.locked_status:
self.locked_status = True
return True
else:
return False

__enter__ = acquire

def __exit__(self, typ, val, tb):
self.release()

def release(self):
"""Release the dummy lock."""
# XXX Perhaps shouldn't actually bother to test? Could lead
# to problems for complex, threaded code.
if not self.locked_status:
raise error
self.locked_status = False
return True

def locked(self):
return self.locked_status

# Used to signal that interrupt_main was called in a "thread"
_interrupt = False
# True when not executing in a "thread"
_main = True

def interrupt_main():
"""Set _interrupt flag to True to have start_new_thread raise
KeyboardInterrupt upon exiting."""
if _main:
raise KeyboardInterrupt
else:
global _interrupt
_interrupt = True