"""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

"""

__author__ = "Brett Cannon"

__email__ = "brett@python.org"

# 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

import warnings

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:

            self.locked_status = True

            return None

        elif not waitflag:

            if not self.locked_status:

                self.locked_status = True

                return True

            else:

                return False

        else:

            self.locked_status = True

            return True

    __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