python - Error: Segmentation fault (core dumped)

Question

Im new in python and am getting a strange error:

Segmentation fault (core dumped)

When i execute the following code:

  class Workspace(QMainWindow, Ui_MainWindow):
    """ This class is for managing the whole GUI `Workspace'.
        Currently a Workspace is similar to a MainWindow
    """

    def __init__(self):
        #p= subprocess.Popen(["java -Xmx256m -jar bin/HelloWorld.jar"],cwd=r'/home/karen/sphinx4-1.0beta5-src/sphinx4-1.0beta5/', shell=True, stdout=subprocess.PIPE, bufsize= 4024)
        try:
            from Queue import Queue, Empty
        except ImportError:
            while True:
    #from queue import Queue, Empty  # python 3.x
                print "error"

        ON_POSIX = 'posix' in sys.builtin_module_names

        def enqueue_output(out, queue):
            for line in iter(out.readline, b''):
                queue.put(line)
            out.close()

        p= Popen(["java -Xmx256m -jar bin/HelloWorld.jar"],cwd=r'/home/karen/sphinx4-1.0beta5-src/sphinx4-1.0beta5/',stdout=PIPE, shell=True, bufsize= 4024)
        q = Queue()
        t = threading.Thread(target=enqueue_output, args=(p.stdout, q))
        #t = Thread(target=enqueue_output, args=(p.stdout, q))
        t.daemon = True # thread dies with the program
        t.start()

# ... do other things here
        def myfunc(q):
            while True:

                try: line = q.get_nowait()
         # or q.get(timeout=.1)
                except Empty:
                    print('Vacio')
                else: # got line
    # ... do something with line

                    print line  


        thread = threading.Thread(target=myfunc, args=(q,))
        thread.start()

This part of code is reading from a program's stdout.When i execute myfunc out of the thread it works ! But when i execute it in the thread fais... Any suggestion?

Answer 1

"Segmentation fault (core dumped)" is the string that Linux prints when a program exits with a SIGSEGV signal and you have core creation enabled. This means some program has crashed.

If you're actually getting this error from running Python, this means the Python interpreter has crashed. There are only a few reasons this can happen:

1. You're using a third-party extension module written in C, and that extension module has crashed.

2. You're (directly or indirectly) using the built-in module ctypes, and calling external code that crashes.

3. There's something wrong with your Python installation.

4. You've discovered a bug in Python that you should report.

The first is by far the most common. If your q is an instance of some object from some third-party extension module, you may want to look at the documentation.

Often, when C modules crash, it's because you're doing something which is invalid, or at least uncommon and untested. But whether it's your "fault" in that sense or not - that doesn't matter. The module should raise a Python exception that you can debug, instead of crashing. So, you should probably report a bug to whoever wrote the extension. But meanwhile, rather than waiting 6 months for the bug to be fixed and a new version to come out, you need to figure out what you did that triggered the crash, and whether there's some different way to do what you want. Or switch to a different library.

On the other hand, since you're reading and printing out data from somewhere else, it's possible that your Python interpreter just read the line "Segmentation fault (core dumped)" and faithfully printed what it read. In that case, some other program upstream presumably crashed. (It's even possible that nobody crashed—if you fetched this page from the web and printed it out, you'd get that same line, right?) In your case, based on your comment, it's probably the Java program that crashed.

If you're not sure which case it is (and don't want to learn how to do process management, core-file inspection, or C-level debugging today), there's an easy way to test: After print line add a line saying print "And I'm OK". If you see that after the Segmentation fault line, then Python didn't crash, someone else did. If you don't see it, then it's probably Python that's crashed.