tr_sandbox.r2py

"""
<Program Name>
  tr_sandbox.r2py

<Started>
  March, 2011

<Author>
  Lukas Puehringer, University of Vienna
  lukas.puehringer@univie.ac.at

"""



class Sandbox:
  """
  <Purpose>
    A Sandbox is an isolated space that each user receives when requesting
    the Try Repy webinterface. Each Sandbox has its own context to evaluate
    Repy code using VitualNamespaces and some logging facilities.

    Additionally the Sandbox wraps used Repy functions, mainly in order to isolate
    it from other Sandboxes.

  <Example Use>
    Creation
      Sandbox(user_id, context_dictionary, global_runtime)
    Evaluation
      Sandbox.evaluate(code, callargs)
    Retrieve Current Log Buffer
      Sandbox.getLog()
      ...
  """

  def __init__(self, user_id, context, global_runtime):
    """
    <Purpose>
      Sandbox Constructor
      It wraps the Sandboxes Context Functions and instantiates
      variables and locks for logging and thread accounting.

    <Arguments>
      user_id (string)
      context (dict)
        A copy of a clean context, in which global functions dedicated
        to the webcontroller are not included.
      global_runtime (float)
        Used to wrap the Sandboxes runtime.

    """

    self.user = user_id
    self.context = context

    # Prepare the sandbox context
    self.context_wrap()

    self.start_time = getruntime() - global_runtime

    self.log = {}
    self.log_lock = createlock()

    self.tmp_logtime = ""
    self.tmp_output_buffer = ""

    self.lock_output_buffer = createlock()

    # Used for thread accounting
    self.thread_count = 0
    self.thread_lock = createlock()
    self.thread_accounting_lock = createlock()



  def my_log(self, *args):
    """
    <Purpose>
      Override The Repy log function to safe the evaluation output
      to a log dictionary and a current log buffer.

    <Arguments>
      *args
        The output which would be normally written to stdout.

    """
    self.log_lock.acquire(True)
    for arg in args:
      if arg != self:
        self.log[self.tmp_logtime]["output"] += str(arg) + " "
        self.write_output_buffer( (str(arg) + " ") )
    self.log[self.tmp_logtime]["output"] += "\n"
    self.write_output_buffer("\n")
    self.log_lock.release()

  def context_wrap(self):
    """
    <Purpose>
      This makes sure that a Sandbox context is completely isolated
      from other contexti.
      Per default a Context copy is a shallow copy. Here we make sure
      that deeper layers of the Context do not contain any References
      shared between the contexti.
      Additionally we wrap most of the repy functions to perform according
      to our custom needs.

    """
    #Initialize clean mycontext dict and callargs list
    self.context["mycontext"] = {}
    self.context["callargs"] = []

    ##
    # General wrappers

    def wrapped_log(*args):
      self.my_log(*args)
    self.context["log"] = wrapped_log

    def wrapped_getruntime():
      return (getruntime() - self.start_time)
    self.context["getruntime"] = wrapped_getruntime

    # This prevents user from kill the entire Application.
    def wrapped_exitall():
      pass
    self.context["exitall"] = wrapped_exitall

    ##
    # File wrappers

    def wrapped_listdir():
      return tr_listdir(self.user)
    self.context["listdir"] = wrapped_listdir

    def wrapped_open(*args):
      return tr_open(self.user, *args)
    self.context["open"] = wrapped_open

    def wrapped_removefile(*args):
      return tr_removefile(self.user, *args)
    self.context["removefile"] = wrapped_removefile

    ##
    # Timer wrappers

    def wrapped_settimer(time, callbackfunction, args):
      self.thread_register()

      def wrapped_callbackfunction(*args):
        try:
          callbackfunction(*args[0])
        except Exception, e:
          # What do I do with this exception?
          # A caught exception should bring the programm down.
          # But for the moment it is only printed to the Shell
          # were the webcontroller is called.
          error_message = "ThreadException: " + str(e) + \
            "\nCaution: Other threads could still be running!"
          self.my_log(error_message)
        self.thread_deregister()

      return settimer(time, wrapped_callbackfunction, [args])
    self.context['settimer'] = wrapped_settimer

    def wrapped_canceltimer(timerhandle):
      ret = canceltimer(timerhandle)
      if ret:
        self.thread_deregister()
      return ret
    self.context['canceltimer'] = wrapped_canceltimer

    ##
    # Network wrappers

    def wrapped_stopcomm(commhandle):
      ret = stopcomm(commhandle)
      if ret:
        self.thread_deregister()
      return ret
    self.context['stopcomm'] = wrapped_stopcomm


    def wrapped_recvmess(localip, localport, function):
      self.thread_register() # This registers the listening thread

      def wrapped_callback_udp(remIP, remport, message, commhandle):
        self.thread_register()
        try:
          function(remIP, remport, message, commhandle)
        except Exception, e:
          # What do I do with this exception?
          # A caught exception should bring the programm down.
          # But for the moment it is only printed to the Shell
          # were the webcontroller is called.
          error_message = "ThreadException: " + str(e) + \
            "\nCaution: Other threads could still be running!"
          self.my_log(error_message)
        self.thread_deregister()

      return recvmess(localip, localport, wrapped_callback_udp)
    self.context['recvmess'] = wrapped_recvmess


    def wrapped_waitforconn(ip, port, callbackfunction):
      self.thread_register()

      def wrapped_callback_tcp(remip, remport, so, thishandle, listenhandle):
        self.thread_register()
        try:
          callbackfunction(remip, remport, so, thishandle, listenhandle)
        except Exception, e:
          # What do I do with this exception?
          # A caught exception should bring the programm down.
          # But for the moment it is only printed to the Shell
          # were the webcontroller is called.
          error_message = "ThreadException: " + str(e) + \
            "\nCaution: Other threads could still be running!"
          self.my_log(error_message)
          log("Exception: " + str(e))
        self.thread_deregister()

      return waitforconn(ip, port, wrapped_callback_tcp)
    self.context['waitforconn'] = wrapped_waitforconn

    # This makes sure, that the _context dict Sandboxes context
    # is not a reference shared with other Sandboxes contexti
    self.context["_context"] = self.context


  def evaluate_repy(self, user_code, user_callargs):

    # Reset the current outputbuffer
    self.tmp_output_buffer = ""

    # Ceate new logentry with a timestamp as key
    # This thimestamp is temporarily stored as attribute to access it
    # in the loggin wrapper.
    self.tmp_logtime = self.context["getruntime"]()
    self.log[self.tmp_logtime] = {}
    self.log[self.tmp_logtime]["code"] = user_code
    self.log[self.tmp_logtime]["output"] = ""
    self.context["callargs"] = user_callargs

    try:
      # Create a new VirtualNamespace for the code
      # and evaluate it in the Sandboxes context.
      tmp_virt = createvirtualnamespace(user_code, "tryrepy")
      tmp_virt.evaluate(self.context)

    except Exception, e:

      # This message is written to the log and the output buffer.
      error_message = "MainThreadException: " + str(e) + \
        "\nCaution: Other threads could still be running!"

      self.my_log(error_message)


    # Wait, maybe a thread is about to register.
    sleep(0.5)

    # The last active not-main thread will release this lock.
    # Until then, the main (this) thread is blocked.
    if self.thread_count:
      self.thread_lock.acquire(True)
      self.thread_lock.release()

    # Read the remaining output buffer.
    # Nothing should be written to the buffer afterwards.
    output = self.read_output_buffer()

    # Return what is left of the output buffer.
    return output


  def read_output_buffer(self):
    """
    <Purpose>
      Safely empty the output buffer.

    <Returns>
      output (string)
        The current output buffer.

    """
    self.lock_output_buffer.acquire(True)
    output = self.tmp_output_buffer
    self.tmp_output_buffer = ""
    self.lock_output_buffer.release()
    return output


  def write_output_buffer(self, data):
    """
    <Purpose>
      Safely write to the output buffer.

    <Arguments>
      data (string)
        The output that would be usually written to stdout.

    """
    self.lock_output_buffer.acquire(True)
    self.tmp_output_buffer += data
    self.lock_output_buffer.release()


  def get_log(self):
    """
    <Purpose>
      Return the entire current Sandbox log.
      XXX: Is this problematic? If it is only read.
      XXX: There should be no race condition??

    <Returns>
      log_dict (dict)

    """
    return self.log

  def thread_register(self):
    """
    <Purpose>
      Safely account a new thread for the current evaluation.
      If it is the first thread a lock is acquired.
      The lock makes sure that the main thread waits until
      all threads are terminated and not till then signals
      that the entire evaluation has terminated.

    """
    self.thread_accounting_lock.acquire(True)
    if not self.thread_count:
      self.thread_lock.acquire(True)
    self.thread_count = self.thread_count + 1
    self.thread_accounting_lock.release()


  def thread_deregister(self):
    """
    <Purpose>
      Safely account that a thread of the current evaluation
      has terminated. If it was the last thread besides the
      main thread, the lock is released which means, the main
      thread can signal terminated of the entire evaluation.

    """
    self.thread_accounting_lock.acquire(True)
    self.thread_count = self.thread_count - 1
    if not self.thread_count:
      self.thread_lock.release()
    self.thread_accounting_lock.release()