#!/usr/bin/env python
# Copyright 2014 the V8 project authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

from Queue import Empty
from contextlib import contextmanager
from multiprocessing import Process, Queue
import os
import signal
import time
import traceback

from . import command


def setup_testing():
  """For testing only: Use threading under the hood instead of multiprocessing
  to make coverage work.
  """
  global Queue
  global Process
  del Queue
  del Process
  from Queue import Queue
  from threading import Thread as Process
  # Monkeypatch threading Queue to look like multiprocessing Queue.
  Queue.cancel_join_thread = lambda self: None
  # Monkeypatch os.kill and add fake pid property on Thread.
  os.kill = lambda *args: None
  Process.pid = property(lambda self: None)


class NormalResult():
  def __init__(self, result):
    self.result = result
    self.exception = None

class ExceptionResult():
  def __init__(self, exception):
    self.exception = exception


class MaybeResult():
  def __init__(self, heartbeat, value):
    self.heartbeat = heartbeat
    self.value = value

  @staticmethod
  def create_heartbeat():
    return MaybeResult(True, None)

  @staticmethod
  def create_result(value):
    return MaybeResult(False, value)


def Worker(fn, work_queue, done_queue,
           process_context_fn=None, process_context_args=None):
  """Worker to be run in a child process.
  The worker stops when the poison pill "STOP" is reached.
  """
  try:
    kwargs = {}
    if process_context_fn and process_context_args is not None:
      kwargs.update(process_context=process_context_fn(*process_context_args))
    for args in iter(work_queue.get, "STOP"):
      try:
        done_queue.put(NormalResult(fn(*args, **kwargs)))
      except command.AbortException:
        # SIGINT, SIGTERM or internal hard timeout.
        break
      except Exception, e:
        traceback.print_exc()
        print(">>> EXCEPTION: %s" % e)
        done_queue.put(ExceptionResult(e))
    # When we reach here on normal tear down, all items have been pulled from
    # the done_queue before and this should have no effect. On fast abort, it's
    # possible that a fast worker left items on the done_queue in memory, which
    # will never be pulled. This call purges those to avoid a deadlock.
    done_queue.cancel_join_thread()
  except KeyboardInterrupt:
    assert False, 'Unreachable'


@contextmanager
def without_sig():
  int_handler = signal.signal(signal.SIGINT, signal.SIG_IGN)
  term_handler = signal.signal(signal.SIGTERM, signal.SIG_IGN)
  try:
    yield
  finally:
    signal.signal(signal.SIGINT, int_handler)
    signal.signal(signal.SIGTERM, term_handler)


class Pool():
  """Distributes tasks to a number of worker processes.
  New tasks can be added dynamically even after the workers have been started.
  Requirement: Tasks can only be added from the parent process, e.g. while
  consuming the results generator."""

  # Factor to calculate the maximum number of items in the work/done queue.
  # Necessary to not overflow the queue's pipe if a keyboard interrupt happens.
  BUFFER_FACTOR = 4

  def __init__(self, num_workers, heartbeat_timeout=1):
    self.num_workers = num_workers
    self.processes = []
    self.terminated = False
    self.abort_now = False

    # Invariant: processing_count >= #work_queue + #done_queue. It is greater
    # when a worker takes an item from the work_queue and before the result is
    # submitted to the done_queue. It is equal when no worker is working,
    # e.g. when all workers have finished, and when no results are processed.
    # Count is only accessed by the parent process. Only the parent process is
    # allowed to remove items from the done_queue and to add items to the
    # work_queue.
    self.processing_count = 0
    self.heartbeat_timeout = heartbeat_timeout

    # Disable sigint and sigterm to prevent subprocesses from capturing the
    # signals.
    with without_sig():
      self.work_queue = Queue()
      self.done_queue = Queue()

  def imap_unordered(self, fn, gen,
                     process_context_fn=None, process_context_args=None):
    """Maps function "fn" to items in generator "gen" on the worker processes
    in an arbitrary order. The items are expected to be lists of arguments to
    the function. Returns a results iterator. A result value of type
    MaybeResult either indicates a heartbeat of the runner, i.e. indicating
    that the runner is still waiting for the result to be computed, or it wraps
    the real result.

    Args:
      process_context_fn: Function executed once by each worker. Expected to
          return a process-context object. If present, this object is passed
          as additional argument to each call to fn.
      process_context_args: List of arguments for the invocation of
          process_context_fn. All arguments will be pickled and sent beyond the
          process boundary.
    """
    if self.terminated:
      return
    try:
      internal_error = False
      gen = iter(gen)
      self.advance = self._advance_more

      # Disable sigint and sigterm to prevent subprocesses from capturing the
      # signals.
      with without_sig():
        for w in xrange(self.num_workers):
          p = Process(target=Worker, args=(fn,
                                          self.work_queue,
                                          self.done_queue,
                                          process_context_fn,
                                          process_context_args))
          p.start()
          self.processes.append(p)

      self.advance(gen)
      while self.processing_count > 0:
        while True:
          try:
            # Read from result queue in a responsive fashion. If available,
            # this will return a normal result immediately or a heartbeat on
            # heartbeat timeout (default 1 second).
            result = self._get_result_from_queue()
          except:
            # TODO(machenbach): Handle a few known types of internal errors
            # gracefully, e.g. missing test files.
            internal_error = True
            continue

          if self.abort_now:
            # SIGINT, SIGTERM or internal hard timeout.
            return

          yield result
          break

        self.advance(gen)
    except KeyboardInterrupt:
      assert False, 'Unreachable'
    except Exception as e:
      traceback.print_exc()
      print(">>> EXCEPTION: %s" % e)
    finally:
      self._terminate()

    if internal_error:
      raise Exception("Internal error in a worker process.")

  def _advance_more(self, gen):
    while self.processing_count < self.num_workers * self.BUFFER_FACTOR:
      try:
        self.work_queue.put(gen.next())
        self.processing_count += 1
      except StopIteration:
        self.advance = self._advance_empty
        break

  def _advance_empty(self, gen):
    pass

  def add(self, args):
    """Adds an item to the work queue. Can be called dynamically while
    processing the results from imap_unordered."""
    assert not self.terminated

    self.work_queue.put(args)
    self.processing_count += 1

  def abort(self):
    """Schedules abort on next queue read.

    This is safe to call when handling SIGINT, SIGTERM or when an internal
    hard timeout is reached.
    """
    self.abort_now = True

  def _terminate(self):
    """Terminates execution and cleans up the queues.

    If abort() was called before termination, this also terminates the
    subprocesses and doesn't wait for ongoing tests.
    """
    if self.terminated:
      return
    self.terminated = True

    # Drain out work queue from tests
    try:
      while True:
        self.work_queue.get(True, 0.1)
    except Empty:
      pass

    # Make sure all processes stop
    for _ in self.processes:
      # During normal tear down the workers block on get(). Feed a poison pill
      # per worker to make them stop.
      self.work_queue.put("STOP")

    if self.abort_now:
      for p in self.processes:
        os.kill(p.pid, signal.SIGTERM)

    for p in self.processes:
      p.join()

    # Drain the queues to prevent stderr chatter when queues are garbage
    # collected.
    try:
      while True: self.work_queue.get(False)
    except:
      pass
    try:
      while True: self.done_queue.get(False)
    except:
      pass

  def _get_result_from_queue(self):
    """Attempts to get the next result from the queue.

    Returns: A wrapped result if one was available within heartbeat timeout,
        a heartbeat result otherwise.
    Raises:
        Exception: If an exception occured when processing the task on the
            worker side, it is reraised here.
    """
    while True:
      try:
        result = self.done_queue.get(timeout=self.heartbeat_timeout)
        self.processing_count -= 1
        if result.exception:
          raise result.exception
        return MaybeResult.create_result(result.result)
      except Empty:
        return MaybeResult.create_heartbeat()
