pystuck 0.8.5

Dependancies

• IPython

• rpyc(3.2.3, may work with others)

Droduction Use

pystuck doesn’t consume resources when no client is connected to it.

all the run_server function does is spawn a thread that blocks on accept (waiting for clients to connect), so it can be used in production.

there are two drawbacks for using pystuck in production:

1. meddling with variables and modules is not thread safe.

2. a potential security breach - nothing prevents an unprivilidged user connect to a privlidged running python process and use the remote access to do practically anything.

What is python doing?!

test.py is stuck, wouldn’t you just die to know where?

import pystuck; pystuck.run_server().

while True:
    with lock: # could block
         sock.recv(1024) # could block

running pystuck from the shell shows interesting stuff:

% pystuck
<_MainThread(MainThread, started -1215396160)>
  File "test.py", line 9, in <module>
    with lock: # could block

...

it’s stuck waiting for the lock!. it actually prints two more threads that are related to pystuck, ignore them.

Who’s got the lock?!

# it seldom happens that a thread doesn't release the lock or is stuck while holding it.
# we want to know which thread... bear with me now.
rlock.acquire()

invoking pystuck again:

% pystuck
<_MainThread(MainThread, started -1215396160)>
  File "test.py", line 9, in <module>
    with lock: # could block

<Thread(Thread-1, started -1219450000)>
  File "test.py", line 12, in <module>
    do_math()

<Thread(Thread-2, started -1219540000)>
  File "test.py", line 14, in <module>
    foo()
  File "test.py", line 20, in foo
    do_network()

use the 'modules' dictionary to access remote modules (like 'os', or '__main__')

In [0]: modules['sys']._current_frames() # gets a mapping between a thread to its frame (top of stack)
Out[0]: {-1215396160: <frame object at 0x8a07154>,
         -1219450000: <frame object at 0x8a29154>,
         -1219540000: <frame object at 0x8b39154>}

In [1]: _[-1215396160] # get the stuck thread's frame
Out[1]: <frame object at 0x8a07154>

In [2]: _.f_locals # local variables of the function
Out[2]: {'lock': <_RLock owner=-1219450000 count=1>}

In [3]: # our stuck thread is probably waiting for thread 1219450000 to finish do_math.. figures

What rpyc can do for you

rpyc is the library used to communicate python objects and procedure calls across processes. here are some of the things you can do to the already running server.

% pystuck

(stacks appear here...)

In [1]: modules['sys'].stdout = file("/tmp/log.txt", "w") # tunnel the script's stdout to log

In [2]: modules['__main__'].global_var = 100 # change and inspect variables in the __main__ module (the name of the script when invoked like this: python script.py)

In [3]: socket = modules['socket'].socket() # create a socket object opened by the server script!