kafka/consumer.py

from __future__ import absolute_import

from itertools import izip_longest, repeat
import logging
import time
from threading import Lock
from multiprocessing import Process, Queue as MPQueue, Event, Value
from Queue import Empty, Queue

from kafka.common import (
    ErrorMapping, FetchRequest,
    OffsetRequest, OffsetCommitRequest,
    ConsumerFetchSizeTooSmall, ConsumerNoMoreData
)

from kafka.util import ReentrantTimer

log = logging.getLogger("kafka")

AUTO_COMMIT_MSG_COUNT = 100
AUTO_COMMIT_INTERVAL = 5000

FETCH_DEFAULT_BLOCK_TIMEOUT = 1
FETCH_MAX_WAIT_TIME = 100
FETCH_MIN_BYTES = 4096
FETCH_BUFFER_SIZE_BYTES = 4096
MAX_FETCH_BUFFER_SIZE_BYTES = FETCH_BUFFER_SIZE_BYTES * 8

ITER_TIMEOUT_SECONDS = 60
NO_MESSAGES_WAIT_TIME_SECONDS = 0.1


class FetchContext(object):
    """
    Class for managing the state of a consumer during fetch
    """
    def __init__(self, consumer, block, timeout):
        self.consumer = consumer
        self.block = block

        if block:
            if not timeout:
                timeout = FETCH_DEFAULT_BLOCK_TIMEOUT
            self.timeout = timeout * 1000

    def __enter__(self):
        """Set fetch values based on blocking status"""
        self.orig_fetch_max_wait_time = self.consumer.fetch_max_wait_time
        self.orig_fetch_min_bytes = self.consumer.fetch_min_bytes
        if self.block:
            self.consumer.fetch_max_wait_time = self.timeout
            self.consumer.fetch_min_bytes = 1
        else:
            self.consumer.fetch_min_bytes = 0

    def __exit__(self, type, value, traceback):
        """Reset values"""
        self.consumer.fetch_max_wait_time = self.orig_fetch_max_wait_time
        self.consumer.fetch_min_bytes = self.orig_fetch_min_bytes


class Consumer(object):
    """
    Base class to be used by other consumers. Not to be used directly

    This base class provides logic for
    * initialization and fetching metadata of partitions
    * Auto-commit logic
    * APIs for fetching pending message count
    """
    def __init__(self, client, group, topic, partitions=None, auto_commit=True,
                 auto_commit_every_n=AUTO_COMMIT_MSG_COUNT,
                 auto_commit_every_t=AUTO_COMMIT_INTERVAL):

        self.client = client
        self.topic = topic
        self.group = group
        self.client.load_metadata_for_topics(topic)
        self.offsets = {}

        if not partitions:
            partitions = self.client.topic_partitions[topic]

        # Variables for handling offset commits
        self.commit_lock = Lock()
        self.commit_timer = None
        self.count_since_commit = 0
        self.auto_commit = auto_commit
        self.auto_commit_every_n = auto_commit_every_n
        self.auto_commit_every_t = auto_commit_every_t

        # Set up the auto-commit timer
        if auto_commit is True and auto_commit_every_t is not None:
            self.commit_timer = ReentrantTimer(auto_commit_every_t,
                                               self.commit)
            self.commit_timer.start()

        def get_or_init_offset_callback(resp):
            if resp.error == ErrorMapping.NO_ERROR:
                return resp.offset
            elif resp.error == ErrorMapping.UNKNOWN_TOPIC_OR_PARTITON:
                return 0
            else:
                raise Exception("OffsetFetchRequest for topic=%s, "
                                "partition=%d failed with errorcode=%s" % (
                                    resp.topic, resp.partition, resp.error))

        # Uncomment for 0.8.1
        #
        #for partition in partitions:
        #    req = OffsetFetchRequest(topic, partition)
        #    (offset,) = self.client.send_offset_fetch_request(group, [req],
        #                  callback=get_or_init_offset_callback,
        #                  fail_on_error=False)
        #    self.offsets[partition] = offset

        for partition in partitions:
            self.offsets[partition] = 0

    def commit(self, partitions=None):
        """
        Commit offsets for this consumer

        partitions: list of partitions to commit, default is to commit
                    all of them
        """

        # short circuit if nothing happened. This check is kept outside
        # to prevent un-necessarily acquiring a lock for checking the state
        if self.count_since_commit == 0:
            return

        with self.commit_lock:
            # Do this check again, just in case the state has changed
            # during the lock acquiring timeout
            if self.count_since_commit == 0:
                return

            reqs = []
            if not partitions:  # commit all partitions
                partitions = self.offsets.keys()

            for partition in partitions:
                offset = self.offsets[partition]
                log.debug("Commit offset %d in SimpleConsumer: "
                          "group=%s, topic=%s, partition=%s" %
                          (offset, self.group, self.topic, partition))

                reqs.append(OffsetCommitRequest(self.topic, partition,
                                                offset, None))

            resps = self.client.send_offset_commit_request(self.group, reqs)
            for resp in resps:
                assert resp.error == 0

            self.count_since_commit = 0

    def _auto_commit(self):
        """
        Check if we have to commit based on number of messages and commit
        """

        # Check if we are supposed to do an auto-commit
        if not self.auto_commit or self.auto_commit_every_n is None:
            return

        if self.count_since_commit > self.auto_commit_every_n:
            self.commit()

    def stop(self):
        if self.commit_timer is not None:
            self.commit_timer.stop()
            self.commit()

    def pending(self, partitions=None):
        """
        Gets the pending message count

        partitions: list of partitions to check for, default is to check all
        """
        if not partitions:
            partitions = self.offsets.keys()

        total = 0
        reqs = []

        for partition in partitions:
            reqs.append(OffsetRequest(self.topic, partition, -1, 1))

        resps = self.client.send_offset_request(reqs)
        for resp in resps:
            partition = resp.partition
            pending = resp.offsets[0]
            offset = self.offsets[partition]
            total += pending - offset - (1 if offset > 0 else 0)

        return total


class SimpleConsumer(Consumer):
    """
    A simple consumer implementation that consumes all/specified partitions
    for a topic

    client: a connected KafkaClient
    group: a name for this consumer, used for offset storage and must be unique
    topic: the topic to consume
    partitions: An optional list of partitions to consume the data from

    auto_commit: default True. Whether or not to auto commit the offsets
    auto_commit_every_n: default 100. How many messages to consume
                         before a commit
    auto_commit_every_t: default 5000. How much time (in milliseconds) to
                         wait before commit
    fetch_size_bytes:    number of bytes to request in a FetchRequest
    buffer_size:         default 4K. Initial number of bytes to tell kafka we
                         have available. This will double as needed.
    max_buffer_size:     default 16K. Max number of bytes to tell kafka we have
                         available. None means no limit.
    iter_timeout:        default None. How much time (in seconds) to wait for a
                         message in the iterator before exiting. None means no
                         timeout, so it will wait forever.

    Auto commit details:
    If both auto_commit_every_n and auto_commit_every_t are set, they will
    reset one another when one is triggered. These triggers simply call the
    commit method on this class. A manual call to commit will also reset
    these triggers
    """
    def __init__(self, client, group, topic, auto_commit=True, partitions=None,
                 auto_commit_every_n=AUTO_COMMIT_MSG_COUNT,
                 auto_commit_every_t=AUTO_COMMIT_INTERVAL,
                 fetch_size_bytes=FETCH_MIN_BYTES,
                 buffer_size=FETCH_BUFFER_SIZE_BYTES,
                 max_buffer_size=MAX_FETCH_BUFFER_SIZE_BYTES,
                 iter_timeout=None):
        super(SimpleConsumer, self).__init__(
            client, group, topic,
            partitions=partitions,
            auto_commit=auto_commit,
            auto_commit_every_n=auto_commit_every_n,
            auto_commit_every_t=auto_commit_every_t)

        if max_buffer_size is not None and buffer_size > max_buffer_size:
            raise ValueError("buffer_size (%d) is greater than "
                             "max_buffer_size (%d)" %
                             (buffer_size, max_buffer_size))
        self.buffer_size = buffer_size
        self.max_buffer_size = max_buffer_size
        self.partition_info = False     # Do not return partition info in msgs
        self.fetch_max_wait_time = FETCH_MAX_WAIT_TIME
        self.fetch_min_bytes = fetch_size_bytes
        self.fetch_offsets = self.offsets.copy()
        self.iter_timeout = iter_timeout
        self.queue = Queue()

    def __repr__(self):
        return '<SimpleConsumer group=%s, topic=%s, partitions=%s>' % \
            (self.group, self.topic, str(self.offsets.keys()))

    def provide_partition_info(self):
        """
        Indicates that partition info must be returned by the consumer
        """
        self.partition_info = True

    def seek(self, offset, whence):
        """
        Alter the current offset in the consumer, similar to fseek

        offset: how much to modify the offset
        whence: where to modify it from
                0 is relative to the earliest available offset (head)
                1 is relative to the current offset
                2 is relative to the latest known offset (tail)
        """

        if whence == 1:  # relative to current position
            for partition, _offset in self.offsets.items():
                self.offsets[partition] = _offset + offset
        elif whence in (0, 2):  # relative to beginning or end
            # divide the request offset by number of partitions,
            # distribute the remained evenly
            (delta, rem) = divmod(offset, len(self.offsets))
            deltas = {}
            for partition, r in izip_longest(self.offsets.keys(),
                                             repeat(1, rem), fillvalue=0):
                deltas[partition] = delta + r

            reqs = []
            for partition in self.offsets.keys():
                if whence == 0:
                    reqs.append(OffsetRequest(self.topic, partition, -2, 1))
                elif whence == 2:
                    reqs.append(OffsetRequest(self.topic, partition, -1, 1))
                else:
                    pass

            resps = self.client.send_offset_request(reqs)
            for resp in resps:
                self.offsets[resp.partition] = \
                    resp.offsets[0] + deltas[resp.partition]
        else:
            raise ValueError("Unexpected value for `whence`, %d" % whence)

        # Reset queue and fetch offsets since they are invalid
        self.fetch_offsets = self.offsets.copy()
        self.queue = Queue()

    def get_messages(self, count=1, block=True, timeout=0.1):
        """
        Fetch the specified number of messages

        count: Indicates the maximum number of messages to be fetched
        block: If True, the API will block till some messages are fetched.
        timeout: If block is True, the function will block for the specified
                 time (in seconds) until count messages is fetched. If None,
                 it will block forever.
        """
        messages = []
        if timeout is not None:
            max_time = time.time() + timeout

        new_offsets = {}
        while count > 0 and (timeout is None or timeout > 0):
            result = self._get_message(block, timeout, get_partition_info=True,
                                       update_offset=False)
            if result:
                partition, message = result
                if self.partition_info:
                    messages.append(result)
                else:
                    messages.append(message)
                new_offsets[partition] = message.offset + 1
                count -= 1
            else:
                # Ran out of messages for the last request.
                if not block:
                    # If we're not blocking, break.
                    break
                if timeout is not None:
                    # If we're blocking and have a timeout, reduce it to the
                    # appropriate value
                    timeout = max_time - time.time()

        # Update and commit offsets if necessary
        self.offsets.update(new_offsets)
        self.count_since_commit += len(messages)
        self._auto_commit()
        return messages

    def get_message(self, block=True, timeout=0.1, get_partition_info=None):
        return self._get_message(block, timeout, get_partition_info)

    def _get_message(self, block=True, timeout=0.1, get_partition_info=None,
                     update_offset=True):
        """
        If no messages can be fetched, returns None.
        If get_partition_info is None, it defaults to self.partition_info
        If get_partition_info is True, returns (partition, message)
        If get_partition_info is False, returns message
        """
        if self.queue.empty():
            # We're out of messages, go grab some more.
            with FetchContext(self, block, timeout):
                self._fetch()
        try:
            partition, message = self.queue.get_nowait()

            if update_offset:
                # Update partition offset
                self.offsets[partition] = message.offset + 1

                # Count, check and commit messages if necessary
                self.count_since_commit += 1
                self._auto_commit()

            if get_partition_info is None:
                get_partition_info = self.partition_info
            if get_partition_info:
                return partition, message
            else:
                return message
        except Empty:
            return None

    def __iter__(self):
        if self.iter_timeout is None:
            timeout = ITER_TIMEOUT_SECONDS
        else:
            timeout = self.iter_timeout

        while True:
            message = self.get_message(True, timeout)
            if message:
                yield message
            elif self.iter_timeout is None:
                # We did not receive any message yet but we don't have a
                # timeout, so give up the CPU for a while before trying again
                time.sleep(NO_MESSAGES_WAIT_TIME_SECONDS)
            else:
                # Timed out waiting for a message
                break

    def _fetch(self):
        # Create fetch request payloads for all the partitions
        requests = []
        partitions = self.fetch_offsets.keys()
        while partitions:
            for partition in partitions:
                requests.append(FetchRequest(self.topic, partition,
                                             self.fetch_offsets[partition],
                                             self.buffer_size))
            # Send request
            responses = self.client.send_fetch_request(
                requests,
                max_wait_time=int(self.fetch_max_wait_time),
                min_bytes=self.fetch_min_bytes)

            retry_partitions = set()
            for resp in responses:
                partition = resp.partition
                try:
                    for message in resp.messages:
                        # Put the message in our queue
                        self.queue.put((partition, message))
                        self.fetch_offsets[partition] = message.offset + 1
                except ConsumerFetchSizeTooSmall, e:
                    if (self.max_buffer_size is not None and
                            self.buffer_size == self.max_buffer_size):
                        log.error("Max fetch size %d too small",
                                  self.max_buffer_size)
                        raise e
                    if self.max_buffer_size is None:
                        self.buffer_size *= 2
                    else:
                        self.buffer_size = max(self.buffer_size * 2,
                                               self.max_buffer_size)
                    log.warn("Fetch size too small, increase to %d (2x) "
                             "and retry", self.buffer_size)
                    retry_partitions.add(partition)
                except ConsumerNoMoreData, e:
                    log.debug("Iteration was ended by %r", e)
                except StopIteration:
                    # Stop iterating through this partition
                    log.debug("Done iterating over partition %s" % partition)
                partitions = retry_partitions

def _mp_consume(client, group, topic, chunk, queue, start, exit, pause, size):
    """
    A child process worker which consumes messages based on the
    notifications given by the controller process

    NOTE: Ideally, this should have been a method inside the Consumer
    class. However, multiprocessing module has issues in windows. The
    functionality breaks unless this function is kept outside of a class
    """

    # Make the child processes open separate socket connections
    client.reinit()

    # We will start consumers without auto-commit. Auto-commit will be
    # done by the master controller process.
    consumer = SimpleConsumer(client, group, topic,
                              partitions=chunk,
                              auto_commit=False,
                              auto_commit_every_n=None,
                              auto_commit_every_t=None)

    # Ensure that the consumer provides the partition information
    consumer.provide_partition_info()

    while True:
        # Wait till the controller indicates us to start consumption
        start.wait()

        # If we are asked to quit, do so
        if exit.is_set():
            break

        # Consume messages and add them to the queue. If the controller
        # indicates a specific number of messages, follow that advice
        count = 0

        message = consumer.get_message()
        if message:
            queue.put(message)
            count += 1

            # We have reached the required size. The controller might have
            # more than what he needs. Wait for a while.
            # Without this logic, it is possible that we run into a big
            # loop consuming all available messages before the controller
            # can reset the 'start' event
            if count == size.value:
                pause.wait()

        else:
            # In case we did not receive any message, give up the CPU for
            # a while before we try again
            time.sleep(NO_MESSAGES_WAIT_TIME_SECONDS)

    consumer.stop()


class MultiProcessConsumer(Consumer):
    """
    A consumer implementation that consumes partitions for a topic in
    parallel using multiple processes

    client: a connected KafkaClient
    group: a name for this consumer, used for offset storage and must be unique
    topic: the topic to consume

    auto_commit: default True. Whether or not to auto commit the offsets
    auto_commit_every_n: default 100. How many messages to consume
                         before a commit
    auto_commit_every_t: default 5000. How much time (in milliseconds) to
                         wait before commit
    num_procs: Number of processes to start for consuming messages.
               The available partitions will be divided among these processes
    partitions_per_proc: Number of partitions to be allocated per process
               (overrides num_procs)

    Auto commit details:
    If both auto_commit_every_n and auto_commit_every_t are set, they will
    reset one another when one is triggered. These triggers simply call the
    commit method on this class. A manual call to commit will also reset
    these triggers
    """
    def __init__(self, client, group, topic, auto_commit=True,
                 auto_commit_every_n=AUTO_COMMIT_MSG_COUNT,
                 auto_commit_every_t=AUTO_COMMIT_INTERVAL,
                 num_procs=1, partitions_per_proc=0):

        # Initiate the base consumer class
        super(MultiProcessConsumer, self).__init__(
            client, group, topic,
            partitions=None,
            auto_commit=auto_commit,
            auto_commit_every_n=auto_commit_every_n,
            auto_commit_every_t=auto_commit_every_t)

        # Variables for managing and controlling the data flow from
        # consumer child process to master
        self.queue = MPQueue(1024)  # Child consumers dump messages into this
        self.start = Event()        # Indicates the consumers to start fetch
        self.exit = Event()         # Requests the consumers to shutdown
        self.pause = Event()        # Requests the consumers to pause fetch
        self.size = Value('i', 0)   # Indicator of number of messages to fetch

        partitions = self.offsets.keys()

        # If unspecified, start one consumer per partition
        # The logic below ensures that
        # * we do not cross the num_procs limit
        # * we have an even distribution of partitions among processes
        if not partitions_per_proc:
            partitions_per_proc = round(len(partitions) * 1.0 / num_procs)
            if partitions_per_proc < num_procs * 0.5:
                partitions_per_proc += 1

        # The final set of chunks
        chunker = lambda *x: [] + list(x)
        chunks = map(chunker, *[iter(partitions)] * int(partitions_per_proc))

        self.procs = []
        for chunk in chunks:
            chunk = filter(lambda x: x is not None, chunk)
            args = (client.copy(),
                    group, topic, chunk,
                    self.queue, self.start, self.exit,
                    self.pause, self.size)

            proc = Process(target=_mp_consume, args=args)
            proc.daemon = True
            proc.start()
            self.procs.append(proc)

    def __repr__(self):
        return '<MultiProcessConsumer group=%s, topic=%s, consumers=%d>' % \
            (self.group, self.topic, len(self.procs))

    def stop(self):
        # Set exit and start off all waiting consumers
        self.exit.set()
        self.pause.set()
        self.start.set()

        for proc in self.procs:
            proc.join()
            proc.terminate()

        super(MultiProcessConsumer, self).stop()

    def __iter__(self):
        """
        Iterator to consume the messages available on this consumer
        """
        # Trigger the consumer procs to start off.
        # We will iterate till there are no more messages available
        self.size.value = 0
        self.pause.set()

        while True:
            self.start.set()
            try:
                # We will block for a small while so that the consumers get
                # a chance to run and put some messages in the queue
                # TODO: This is a hack and will make the consumer block for
                # at least one second. Need to find a better way of doing this
                partition, message = self.queue.get(block=True, timeout=1)
            except Empty:
                break

            # Count, check and commit messages if necessary
            self.offsets[partition] = message.offset + 1
            self.start.clear()
            self.count_since_commit += 1
            self._auto_commit()
            yield message

        self.start.clear()

    def get_messages(self, count=1, block=True, timeout=10):
        """
        Fetch the specified number of messages

        count: Indicates the maximum number of messages to be fetched
        block: If True, the API will block till some messages are fetched.
        timeout: If block is True, the function will block for the specified
                 time (in seconds) until count messages is fetched. If None,
                 it will block forever.
        """
        messages = []

        # Give a size hint to the consumers. Each consumer process will fetch
        # a maximum of "count" messages. This will fetch more messages than
        # necessary, but these will not be committed to kafka. Also, the extra
        # messages can be provided in subsequent runs
        self.size.value = count
        self.pause.clear()

        if timeout is not None:
            max_time = time.time() + timeout

        new_offsets = {}
        while count > 0 and (timeout is None or timeout > 0):
            # Trigger consumption only if the queue is empty
            # By doing this, we will ensure that consumers do not
            # go into overdrive and keep consuming thousands of
            # messages when the user might need only a few
            if self.queue.empty():
                self.start.set()

            try:
                partition, message = self.queue.get(block, timeout)
            except Empty:
                break

            messages.append(message)
            new_offsets[partition] = message.offset + 1
            count -= 1
            if timeout is not None:
                timeout = max_time - time.time()

        self.size.value = 0
        self.start.clear()
        self.pause.set()

        # Update and commit offsets if necessary
        self.offsets.update(new_offsets)
        self.count_since_commit += len(messages)
        self._auto_commit()

        return messages


class ConsoleConsumer(SimpleConsumer):
    def run(self):
        for message in self:
            print(message.message.value)