'''Enhanced threading.Thread which can deliver a return value and propagate
exceptions from the called thread to the calling thread.

Copyright (C) 2007 Canonical Ltd.
Author: Martin Pitt <martin.pitt@ubuntu.com>

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.  See http://www.gnu.org/copyleft/gpl.html for
the full text of the license.
'''

import threading, sys

class REThread(threading.Thread):
    '''Enhanced threading.Thread which can deliver a return value and propagate
    exceptions from the called thread to the calling thread.'''

    def __init__(self, group=None, target=None, name=None, args=(), kwargs={},
            verbose=None):
        '''Initialize Thread, identical to threading.Thread.__init__().'''
        #Note that due to api differences in python (verbose disappeared
        #at some point before 3.3 and got replaced by daemon), we just
        #ignore the verbose attribute. It's not used anywhere in checkbox
        #so this is safe for our purposes.
        self.__target = target
        self.__args = args
        self.__kwargs = kwargs
        self._retval = None
        self._exception = None

        threading.Thread.__init__(self)

    def run(self):
        '''Run target function, identical to threading.Thread.run().'''

        if self.__target:
            try:
                self._retval = self.__target(*self.__args, **self.__kwargs)
            except:
                self._exception = sys.exc_info()

    def return_value(self):
        '''Return value from target function.

        This can only be called after the thread has finished, i. e. when
        isAlive() is False and did not terminate with an exception.'''

        assert not self.isAlive()
        assert not self._exception
        return self._retval

    def exc_info(self):
        '''Return a tuple (type, value, traceback) of the exception caught in
        run().'''

        return self._exception

    def exc_raise(self):
        '''Raises the exception caught in the thread.

        Does nothing if no exception was caught.'''

        if self._exception:
            raise self._exception[0](self._exception[1]).with_traceback(self._exception[2])

#
# Unit test
#

if __name__ == '__main__':
    import unittest, time, traceback, exceptions

    def idle(seconds):
        '''Test thread to just wait a bit.'''

        time.sleep(seconds)

    def div(x, y):
        '''Test thread to divide two numbers.'''

        return x / y

    class _REThreadTest(unittest.TestCase):
        def test_return_value(self):
            '''Test that return value works properly.'''

            t = REThread(target=div, args=(42, 2))
            t.start()
            t.join()
            # exc_raise() should be a no-op on successful functions
            t.exc_raise()
            self.assertEqual(t.return_value(), 21)
            self.assertEqual(t.exc_info(), None)

        def test_no_return_value(self):
            '''Test that REThread works if run() does not return anything.'''

            t = REThread(target=idle, args=(0.5,))
            t.start()
            # thread must be joined first
            self.assertRaises(AssertionError, t.return_value)
            t.join()
            self.assertEqual(t.return_value(), None)
            self.assertEqual(t.exc_info(), None)

        def test_exception(self):
            '''Test that exception in thread is caught and passed.'''

            t = REThread(target=div, args=(1, 0))
            t.start()
            t.join()
            # thread did not terminate normally, no return value
            self.assertRaises(AssertionError, t.return_value)
            self.assert_(t.exc_info()[0] == exceptions.ZeroDivisionError)
            exc = traceback.format_exception(t.exc_info()[0], t.exc_info()[1],
                t.exc_info()[2])
            self.assert_(exc[-1].startswith('ZeroDivisionError'))
            self.assert_(exc[-2].endswith('return x / y\n'))

        def test_exc_raise(self):
            '''Test that exc_raise() raises caught thread exception.'''

            t = REThread(target=div, args=(1, 0))
            t.start()
            t.join()
            # thread did not terminate normally, no return value
            self.assertRaises(AssertionError, t.return_value)
            raised = False
            try:
                t.exc_raise()
            except:
                raised = True
                e = sys.exc_info()
                exc = traceback.format_exception(e[0], e[1], e[2])
                self.assert_(exc[-1].startswith('ZeroDivisionError'))
                self.assert_(exc[-2].endswith('return x / y\n'))
            self.assert_(raised)

    unittest.main()

