worker.py

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

"""
Worker that receives input from Piped RDD.
"""
import os
import sys
import time
from inspect import currentframe, getframeinfo, getfullargspec
import importlib
import json

# 'resource' is a Unix specific module.
has_resource_module = True
try:
    import resource
except ImportError:
    has_resource_module = False
import traceback
import warnings
import faulthandler

from pyspark.accumulators import _accumulatorRegistry
from pyspark.broadcast import Broadcast, _broadcastRegistry
from pyspark.java_gateway import local_connect_and_auth
from pyspark.taskcontext import BarrierTaskContext, TaskContext
from pyspark.files import SparkFiles
from pyspark.resource import ResourceInformation
from pyspark.rdd import PythonEvalType
from pyspark.serializers import (
    write_with_length,
    write_int,
    read_long,
    read_bool,
    write_long,
    read_int,
    SpecialLengths,
    UTF8Deserializer,
    CPickleSerializer,
    BatchedSerializer,
)
from pyspark.sql.pandas.serializers import (
    ArrowStreamPandasUDFSerializer,
    CogroupUDFSerializer,
    ArrowStreamUDFSerializer,
    ApplyInPandasWithStateSerializer,
)
from pyspark.sql.pandas.types import to_arrow_type
from pyspark.sql.types import StructType
from pyspark.util import fail_on_stopiteration, try_simplify_traceback
from pyspark import shuffle

pickleSer = CPickleSerializer()
utf8_deserializer = UTF8Deserializer()


def report_times(outfile, boot, init, finish):
    write_int(SpecialLengths.TIMING_DATA, outfile)
    write_long(int(1000 * boot), outfile)
    write_long(int(1000 * init), outfile)
    write_long(int(1000 * finish), outfile)


def add_path(path):
    # worker can be used, so do not add path multiple times
    if path not in sys.path:
        # overwrite system packages
        sys.path.insert(1, path)


def read_command(serializer, file):
    command = serializer._read_with_length(file)
    if isinstance(command, Broadcast):
        command = serializer.loads(command.value)
    return command


def chain(f, g):
    """chain two functions together"""
    return lambda *a: g(f(*a))


def wrap_udf(f, return_type):
    if return_type.needConversion():
        toInternal = return_type.toInternal
        return lambda *a: toInternal(f(*a))
    else:
        return lambda *a: f(*a)


def wrap_scalar_pandas_udf(f, return_type):
    arrow_return_type = to_arrow_type(return_type)

    def verify_result_type(result):
        if not hasattr(result, "__len__"):
            pd_type = "Pandas.DataFrame" if type(return_type) == StructType else "Pandas.Series"
            raise TypeError(
                "Return type of the user-defined function should be "
                "{}, but is {}".format(pd_type, type(result))
            )
        return result

    def verify_result_length(result, length):
        if len(result) != length:
            raise RuntimeError(
                "Result vector from pandas_udf was not the required length: "
                "expected %d, got %d" % (length, len(result))
            )
        return result

    return lambda *a: (
        verify_result_length(verify_result_type(f(*a)), len(a[0])),
        arrow_return_type,
    )


def wrap_batch_iter_udf(f, return_type):
    arrow_return_type = to_arrow_type(return_type)

    def verify_result_type(result):
        if not hasattr(result, "__len__"):
            pd_type = "Pandas.DataFrame" if type(return_type) == StructType else "Pandas.Series"
            raise TypeError(
                "Return type of the user-defined function should be "
                "{}, but is {}".format(pd_type, type(result))
            )
        return result

    return lambda *iterator: map(
        lambda res: (res, arrow_return_type), map(verify_result_type, f(*iterator))
    )


def verify_pandas_result(result, return_type, assign_cols_by_name):
    import pandas as pd

    if not isinstance(result, pd.DataFrame):
        raise TypeError(
            "Return type of the user-defined function should be "
            "pandas.DataFrame, but is {}".format(type(result))
        )

    # check the schema of the result only if it is not empty or has columns
    if not result.empty or len(result.columns) != 0:
        # if any column name of the result is a string
        # the column names of the result have to match the return type
        #   see create_array in pyspark.sql.pandas.serializers.ArrowStreamPandasSerializer
        field_names = set([field.name for field in return_type.fields])
        column_names = set(result.columns)
        if (
            assign_cols_by_name
            and any(isinstance(name, str) for name in result.columns)
            and column_names != field_names
        ):
            missing = sorted(list(field_names.difference(column_names)))
            missing = f" Missing: {', '.join(missing)}." if missing else ""

            extra = sorted(list(column_names.difference(field_names)))
            extra = f" Unexpected: {', '.join(extra)}." if extra else ""

            raise RuntimeError(
                "Column names of the returned pandas.DataFrame do not match specified schema."
                "{}{}".format(missing, extra)
            )
        # otherwise the number of columns of result have to match the return type
        elif len(result.columns) != len(return_type):
            raise RuntimeError(
                "Number of columns of the returned pandas.DataFrame "
                "doesn't match specified schema. "
                "Expected: {} Actual: {}".format(len(return_type), len(result.columns))
            )


def wrap_cogrouped_map_pandas_udf(f, return_type, argspec, runner_conf):
    _assign_cols_by_name = assign_cols_by_name(runner_conf)

    def wrapped(left_key_series, left_value_series, right_key_series, right_value_series):
        import pandas as pd

        left_df = pd.concat(left_value_series, axis=1)
        right_df = pd.concat(right_value_series, axis=1)

        if len(argspec.args) == 2:
            result = f(left_df, right_df)
        elif len(argspec.args) == 3:
            key_series = left_key_series if not left_df.empty else right_key_series
            key = tuple(s[0] for s in key_series)
            result = f(key, left_df, right_df)
        verify_pandas_result(result, return_type, _assign_cols_by_name)

        return result

    return lambda kl, vl, kr, vr: [(wrapped(kl, vl, kr, vr), to_arrow_type(return_type))]


def wrap_grouped_map_pandas_udf(f, return_type, argspec, runner_conf):
    _assign_cols_by_name = assign_cols_by_name(runner_conf)

    def wrapped(key_series, value_series):
        import pandas as pd

        if len(argspec.args) == 1:
            result = f(pd.concat(value_series, axis=1))
        elif len(argspec.args) == 2:
            key = tuple(s[0] for s in key_series)
            result = f(key, pd.concat(value_series, axis=1))
        verify_pandas_result(result, return_type, _assign_cols_by_name)

        return result

    return lambda k, v: [(wrapped(k, v), to_arrow_type(return_type))]


def wrap_grouped_map_pandas_udf_with_state(f, return_type):
    """
    Provides a new lambda instance wrapping user function of applyInPandasWithState.

    The lambda instance receives (key series, iterator of value series, state) and performs
    some conversion to be adapted with the signature of user function.

    See the function doc of inner function `wrapped` for more details on what adapter does.
    See the function doc of `mapper` function for
    `eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF_WITH_STATE` for more details on
    the input parameters of lambda function.

    Along with the returned iterator, the lambda instance will also produce the return_type as
    converted to the arrow schema.
    """

    def wrapped(key_series, value_series_gen, state):
        """
        Provide an adapter of the user function performing below:

        - Extract the first value of all columns in key series and produce as a tuple.
        - If the state has timed out, call the user function with empty pandas DataFrame.
        - If not, construct a new generator which converts each element of value series to
          pandas DataFrame (lazy evaluation), and call the user function with the generator
        - Verify each element of returned iterator to check the schema of pandas DataFrame.
        """
        import pandas as pd

        key = tuple(s[0] for s in key_series)

        if state.hasTimedOut:
            # Timeout processing pass empty iterator. Here we return an empty DataFrame instead.
            values = [
                pd.DataFrame(columns=pd.concat(next(value_series_gen), axis=1).columns),
            ]
        else:
            values = (pd.concat(x, axis=1) for x in value_series_gen)

        result_iter = f(key, values, state)

        def verify_element(result):
            if not isinstance(result, pd.DataFrame):
                raise TypeError(
                    "The type of element in return iterator of the user-defined function "
                    "should be pandas.DataFrame, but is {}".format(type(result))
                )
            # the number of columns of result have to match the return type
            # but it is fine for result to have no columns at all if it is empty
            if not (
                len(result.columns) == len(return_type)
                or (len(result.columns) == 0 and result.empty)
            ):
                raise RuntimeError(
                    "Number of columns of the element (pandas.DataFrame) in return iterator "
                    "doesn't match specified schema. "
                    "Expected: {} Actual: {}".format(len(return_type), len(result.columns))
                )

            return result

        if isinstance(result_iter, pd.DataFrame):
            raise TypeError(
                "Return type of the user-defined function should be "
                "iterable of pandas.DataFrame, but is {}".format(type(result_iter))
            )

        try:
            iter(result_iter)
        except TypeError:
            raise TypeError(
                "Return type of the user-defined function should be "
                "iterable, but is {}".format(type(result_iter))
            )

        result_iter_with_validation = (verify_element(x) for x in result_iter)

        return (
            result_iter_with_validation,
            state,
        )

    return lambda k, v, s: [(wrapped(k, v, s), to_arrow_type(return_type))]


def wrap_grouped_agg_pandas_udf(f, return_type):
    arrow_return_type = to_arrow_type(return_type)

    def wrapped(*series):
        import pandas as pd

        result = f(*series)
        return pd.Series([result])

    return lambda *a: (wrapped(*a), arrow_return_type)


def wrap_window_agg_pandas_udf(f, return_type, runner_conf, udf_index):
    window_bound_types_str = runner_conf.get("pandas_window_bound_types")
    window_bound_type = [t.strip().lower() for t in window_bound_types_str.split(",")][udf_index]
    if window_bound_type == "bounded":
        return wrap_bounded_window_agg_pandas_udf(f, return_type)
    elif window_bound_type == "unbounded":
        return wrap_unbounded_window_agg_pandas_udf(f, return_type)
    else:
        raise RuntimeError("Invalid window bound type: {} ".format(window_bound_type))


def wrap_unbounded_window_agg_pandas_udf(f, return_type):
    # This is similar to grouped_agg_pandas_udf, the only difference
    # is that window_agg_pandas_udf needs to repeat the return value
    # to match window length, where grouped_agg_pandas_udf just returns
    # the scalar value.
    arrow_return_type = to_arrow_type(return_type)

    def wrapped(*series):
        import pandas as pd

        result = f(*series)
        return pd.Series([result]).repeat(len(series[0]))

    return lambda *a: (wrapped(*a), arrow_return_type)


def wrap_bounded_window_agg_pandas_udf(f, return_type):
    arrow_return_type = to_arrow_type(return_type)

    def wrapped(begin_index, end_index, *series):
        import pandas as pd

        result = []

        # Index operation is faster on np.ndarray,
        # So we turn the index series into np array
        # here for performance
        begin_array = begin_index.values
        end_array = end_index.values

        for i in range(len(begin_array)):
            # Note: Create a slice from a series for each window is
            #       actually pretty expensive. However, there
            #       is no easy way to reduce cost here.
            # Note: s.iloc[i : j] is about 30% faster than s[i: j], with
            #       the caveat that the created slices shares the same
            #       memory with s. Therefore, user are not allowed to
            #       change the value of input series inside the window
            #       function. It is rare that user needs to modify the
            #       input series in the window function, and therefore,
            #       it is be a reasonable restriction.
            # Note: Calling reset_index on the slices will increase the cost
            #       of creating slices by about 100%. Therefore, for performance
            #       reasons we don't do it here.
            series_slices = [s.iloc[begin_array[i] : end_array[i]] for s in series]
            result.append(f(*series_slices))
        return pd.Series(result)

    return lambda *a: (wrapped(*a), arrow_return_type)


def read_single_udf(pickleSer, infile, eval_type, runner_conf, udf_index):
    num_arg = read_int(infile)
    arg_offsets = [read_int(infile) for i in range(num_arg)]
    chained_func = None
    for i in range(read_int(infile)):
        f, return_type = read_command(pickleSer, infile)
        if chained_func is None:
            chained_func = f
        else:
            chained_func = chain(chained_func, f)

    if eval_type == PythonEvalType.SQL_SCALAR_PANDAS_ITER_UDF:
        func = chained_func
    else:
        # make sure StopIteration's raised in the user code are not ignored
        # when they are processed in a for loop, raise them as RuntimeError's instead
        func = fail_on_stopiteration(chained_func)

    # the last returnType will be the return type of UDF
    if eval_type == PythonEvalType.SQL_SCALAR_PANDAS_UDF:
        return arg_offsets, wrap_scalar_pandas_udf(func, return_type)
    elif eval_type == PythonEvalType.SQL_SCALAR_PANDAS_ITER_UDF:
        return arg_offsets, wrap_batch_iter_udf(func, return_type)
    elif eval_type == PythonEvalType.SQL_MAP_PANDAS_ITER_UDF:
        return arg_offsets, wrap_batch_iter_udf(func, return_type)
    elif eval_type == PythonEvalType.SQL_MAP_ARROW_ITER_UDF:
        return arg_offsets, wrap_batch_iter_udf(func, return_type)
    elif eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF:
        argspec = getfullargspec(chained_func)  # signature was lost when wrapping it
        return arg_offsets, wrap_grouped_map_pandas_udf(func, return_type, argspec, runner_conf)
    elif eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF_WITH_STATE:
        return arg_offsets, wrap_grouped_map_pandas_udf_with_state(func, return_type)
    elif eval_type == PythonEvalType.SQL_COGROUPED_MAP_PANDAS_UDF:
        argspec = getfullargspec(chained_func)  # signature was lost when wrapping it
        return arg_offsets, wrap_cogrouped_map_pandas_udf(func, return_type, argspec, runner_conf)
    elif eval_type == PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF:
        return arg_offsets, wrap_grouped_agg_pandas_udf(func, return_type)
    elif eval_type == PythonEvalType.SQL_WINDOW_AGG_PANDAS_UDF:
        return arg_offsets, wrap_window_agg_pandas_udf(func, return_type, runner_conf, udf_index)
    elif eval_type == PythonEvalType.SQL_BATCHED_UDF:
        return arg_offsets, wrap_udf(func, return_type)
    else:
        raise ValueError("Unknown eval type: {}".format(eval_type))


# Used by SQL_GROUPED_MAP_PANDAS_UDF and SQL_SCALAR_PANDAS_UDF when returning StructType
def assign_cols_by_name(runner_conf):
    return (
        runner_conf.get(
            "spark.sql.legacy.execution.pandas.groupedMap.assignColumnsByName", "true"
        ).lower()
        == "true"
    )


def read_udfs(pickleSer, infile, eval_type):
    runner_conf = {}

    if eval_type in (
        PythonEvalType.SQL_SCALAR_PANDAS_UDF,
        PythonEvalType.SQL_COGROUPED_MAP_PANDAS_UDF,
        PythonEvalType.SQL_SCALAR_PANDAS_ITER_UDF,
        PythonEvalType.SQL_MAP_PANDAS_ITER_UDF,
        PythonEvalType.SQL_MAP_ARROW_ITER_UDF,
        PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF,
        PythonEvalType.SQL_GROUPED_AGG_PANDAS_UDF,
        PythonEvalType.SQL_WINDOW_AGG_PANDAS_UDF,
        PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF_WITH_STATE,
    ):

        # Load conf used for pandas_udf evaluation
        num_conf = read_int(infile)
        for i in range(num_conf):
            k = utf8_deserializer.loads(infile)
            v = utf8_deserializer.loads(infile)
            runner_conf[k] = v

        state_object_schema = None
        if eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF_WITH_STATE:
            state_object_schema = StructType.fromJson(json.loads(utf8_deserializer.loads(infile)))

        # NOTE: if timezone is set here, that implies respectSessionTimeZone is True
        timezone = runner_conf.get("spark.sql.session.timeZone", None)
        safecheck = (
            runner_conf.get("spark.sql.execution.pandas.convertToArrowArraySafely", "false").lower()
            == "true"
        )

        if eval_type == PythonEvalType.SQL_COGROUPED_MAP_PANDAS_UDF:
            ser = CogroupUDFSerializer(timezone, safecheck, assign_cols_by_name(runner_conf))
        elif eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF_WITH_STATE:
            arrow_max_records_per_batch = runner_conf.get(
                "spark.sql.execution.arrow.maxRecordsPerBatch", 10000
            )
            arrow_max_records_per_batch = int(arrow_max_records_per_batch)

            ser = ApplyInPandasWithStateSerializer(
                timezone,
                safecheck,
                assign_cols_by_name(runner_conf),
                state_object_schema,
                arrow_max_records_per_batch,
            )
        elif eval_type == PythonEvalType.SQL_MAP_ARROW_ITER_UDF:
            ser = ArrowStreamUDFSerializer()
        else:
            # Scalar Pandas UDF handles struct type arguments as pandas DataFrames instead of
            # pandas Series. See SPARK-27240.
            df_for_struct = (
                eval_type == PythonEvalType.SQL_SCALAR_PANDAS_UDF
                or eval_type == PythonEvalType.SQL_SCALAR_PANDAS_ITER_UDF
                or eval_type == PythonEvalType.SQL_MAP_PANDAS_ITER_UDF
            )
            ser = ArrowStreamPandasUDFSerializer(
                timezone, safecheck, assign_cols_by_name(runner_conf), df_for_struct
            )
    else:
        ser = BatchedSerializer(CPickleSerializer(), 100)

    num_udfs = read_int(infile)

    is_scalar_iter = eval_type == PythonEvalType.SQL_SCALAR_PANDAS_ITER_UDF
    is_map_pandas_iter = eval_type == PythonEvalType.SQL_MAP_PANDAS_ITER_UDF
    is_map_arrow_iter = eval_type == PythonEvalType.SQL_MAP_ARROW_ITER_UDF

    if is_scalar_iter or is_map_pandas_iter or is_map_arrow_iter:
        if is_scalar_iter:
            assert num_udfs == 1, "One SCALAR_ITER UDF expected here."
        if is_map_pandas_iter:
            assert num_udfs == 1, "One MAP_PANDAS_ITER UDF expected here."
        if is_map_arrow_iter:
            assert num_udfs == 1, "One MAP_ARROW_ITER UDF expected here."

        arg_offsets, udf = read_single_udf(pickleSer, infile, eval_type, runner_conf, udf_index=0)

        def func(_, iterator):
            num_input_rows = 0

            def map_batch(batch):
                nonlocal num_input_rows

                udf_args = [batch[offset] for offset in arg_offsets]
                num_input_rows += len(udf_args[0])
                if len(udf_args) == 1:
                    return udf_args[0]
                else:
                    return tuple(udf_args)

            iterator = map(map_batch, iterator)
            result_iter = udf(iterator)

            num_output_rows = 0
            for result_batch, result_type in result_iter:
                num_output_rows += len(result_batch)
                # This assert is for Scalar Iterator UDF to fail fast.
                # The length of the entire input can only be explicitly known
                # by consuming the input iterator in user side. Therefore,
                # it's very unlikely the output length is higher than
                # input length.
                assert (
                    is_map_pandas_iter or is_map_arrow_iter or num_output_rows <= num_input_rows
                ), "Pandas SCALAR_ITER UDF outputted more rows than input rows."
                yield (result_batch, result_type)

            if is_scalar_iter:
                try:
                    next(iterator)
                except StopIteration:
                    pass
                else:
                    raise RuntimeError("pandas iterator UDF should exhaust the input " "iterator.")

                if num_output_rows != num_input_rows:
                    raise RuntimeError(
                        "The length of output in Scalar iterator pandas UDF should be "
                        "the same with the input's; however, the length of output was %d and the "
                        "length of input was %d." % (num_output_rows, num_input_rows)
                    )

        # profiling is not supported for UDF
        return func, None, ser, ser

    def extract_key_value_indexes(grouped_arg_offsets):
        """
        Helper function to extract the key and value indexes from arg_offsets for the grouped and
        cogrouped pandas udfs. See BasePandasGroupExec.resolveArgOffsets for equivalent scala code.

        Parameters
        ----------
        grouped_arg_offsets:  list
            List containing the key and value indexes of columns of the
            DataFrames to be passed to the udf. It consists of n repeating groups where n is the
            number of DataFrames.  Each group has the following format:
                group[0]: length of group
                group[1]: length of key indexes
                group[2.. group[1] +2]: key attributes
                group[group[1] +3 group[0]]: value attributes
        """
        parsed = []
        idx = 0
        while idx < len(grouped_arg_offsets):
            offsets_len = grouped_arg_offsets[idx]
            idx += 1
            offsets = grouped_arg_offsets[idx : idx + offsets_len]
            split_index = offsets[0] + 1
            offset_keys = offsets[1:split_index]
            offset_values = offsets[split_index:]
            parsed.append([offset_keys, offset_values])
            idx += offsets_len
        return parsed

    if eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF:
        # We assume there is only one UDF here because grouped map doesn't
        # support combining multiple UDFs.
        assert num_udfs == 1

        # See FlatMapGroupsInPandasExec for how arg_offsets are used to
        # distinguish between grouping attributes and data attributes
        arg_offsets, f = read_single_udf(pickleSer, infile, eval_type, runner_conf, udf_index=0)
        parsed_offsets = extract_key_value_indexes(arg_offsets)

        # Create function like this:
        #   mapper a: f([a[0]], [a[0], a[1]])
        def mapper(a):
            keys = [a[o] for o in parsed_offsets[0][0]]
            vals = [a[o] for o in parsed_offsets[0][1]]
            return f(keys, vals)

    elif eval_type == PythonEvalType.SQL_GROUPED_MAP_PANDAS_UDF_WITH_STATE:
        # We assume there is only one UDF here because grouped map doesn't
        # support combining multiple UDFs.
        assert num_udfs == 1

        # See FlatMapGroupsInPandas(WithState)Exec for how arg_offsets are used to
        # distinguish between grouping attributes and data attributes
        arg_offsets, f = read_single_udf(pickleSer, infile, eval_type, runner_conf, udf_index=0)
        parsed_offsets = extract_key_value_indexes(arg_offsets)

        def mapper(a):
            """
            The function receives (iterator of data, state) and performs extraction of key and
            value from the data, with retaining lazy evaluation.

            See `load_stream` in `ApplyInPandasWithStateSerializer` for more details on the input
            and see `wrap_grouped_map_pandas_udf_with_state` for more details on how output will
            be used.
            """
            from itertools import tee

            state = a[1]
            data_gen = (x[0] for x in a[0])

            # We know there should be at least one item in the iterator/generator.
            # We want to peek the first element to construct the key, hence applying
            # tee to construct the key while we retain another iterator/generator
            # for values.
            keys_gen, values_gen = tee(data_gen)
            keys_elem = next(keys_gen)
            keys = [keys_elem[o] for o in parsed_offsets[0][0]]

            # This must be generator comprehension - do not materialize.
            vals = ([x[o] for o in parsed_offsets[0][1]] for x in values_gen)

            return f(keys, vals, state)

    elif eval_type == PythonEvalType.SQL_COGROUPED_MAP_PANDAS_UDF:
        # We assume there is only one UDF here because cogrouped map doesn't
        # support combining multiple UDFs.
        assert num_udfs == 1
        arg_offsets, f = read_single_udf(pickleSer, infile, eval_type, runner_conf, udf_index=0)

        parsed_offsets = extract_key_value_indexes(arg_offsets)

        def mapper(a):
            df1_keys = [a[0][o] for o in parsed_offsets[0][0]]
            df1_vals = [a[0][o] for o in parsed_offsets[0][1]]
            df2_keys = [a[1][o] for o in parsed_offsets[1][0]]
            df2_vals = [a[1][o] for o in parsed_offsets[1][1]]
            return f(df1_keys, df1_vals, df2_keys, df2_vals)

    else:
        udfs = []
        for i in range(num_udfs):
            udfs.append(read_single_udf(pickleSer, infile, eval_type, runner_conf, udf_index=i))

        def mapper(a):
            result = tuple(f(*[a[o] for o in arg_offsets]) for (arg_offsets, f) in udfs)
            # In the special case of a single UDF this will return a single result rather
            # than a tuple of results; this is the format that the JVM side expects.
            if len(result) == 1:
                return result[0]
            else:
                return result

    def func(_, it):
        return map(mapper, it)

    # profiling is not supported for UDF
    return func, None, ser, ser


def main(infile, outfile):
    faulthandler_log_path = os.environ.get("PYTHON_FAULTHANDLER_DIR", None)
    try:
        if faulthandler_log_path:
            faulthandler_log_path = os.path.join(faulthandler_log_path, str(os.getpid()))
            faulthandler_log_file = open(faulthandler_log_path, "w")
            faulthandler.enable(file=faulthandler_log_file)

        boot_time = time.time()
        split_index = read_int(infile)
        if split_index == -1:  # for unit tests
            sys.exit(-1)

        version = utf8_deserializer.loads(infile)
        if version != "%d.%d" % sys.version_info[:2]:
            raise RuntimeError(
                (
                    "Python in worker has different version %s than that in "
                    + "driver %s, PySpark cannot run with different minor versions. "
                    + "Please check environment variables PYSPARK_PYTHON and "
                    + "PYSPARK_DRIVER_PYTHON are correctly set."
                )
                % ("%d.%d" % sys.version_info[:2], version)
            )

        # read inputs only for a barrier task
        isBarrier = read_bool(infile)
        boundPort = read_int(infile)
        secret = UTF8Deserializer().loads(infile)

        # set up memory limits
        memory_limit_mb = int(os.environ.get("PYSPARK_EXECUTOR_MEMORY_MB", "-1"))
        if memory_limit_mb > 0 and has_resource_module:
            total_memory = resource.RLIMIT_AS
            try:
                (soft_limit, hard_limit) = resource.getrlimit(total_memory)
                msg = "Current mem limits: {0} of max {1}\n".format(soft_limit, hard_limit)
                print(msg, file=sys.stderr)

                # convert to bytes
                new_limit = memory_limit_mb * 1024 * 1024

                if soft_limit == resource.RLIM_INFINITY or new_limit < soft_limit:
                    msg = "Setting mem limits to {0} of max {1}\n".format(new_limit, new_limit)
                    print(msg, file=sys.stderr)
                    resource.setrlimit(total_memory, (new_limit, new_limit))

            except (resource.error, OSError, ValueError) as e:
                # not all systems support resource limits, so warn instead of failing
                lineno = (
                    getframeinfo(currentframe()).lineno + 1 if currentframe() is not None else 0
                )
                if "__file__" in globals():
                    print(
                        warnings.formatwarning(
                            "Failed to set memory limit: {0}".format(e),
                            ResourceWarning,
                            __file__,
                            lineno,
                        ),
                        file=sys.stderr,
                    )

        # initialize global state
        taskContext = None
        if isBarrier:
            taskContext = BarrierTaskContext._getOrCreate()
            BarrierTaskContext._initialize(boundPort, secret)
            # Set the task context instance here, so we can get it by TaskContext.get for
            # both TaskContext and BarrierTaskContext
            TaskContext._setTaskContext(taskContext)
        else:
            taskContext = TaskContext._getOrCreate()
        # read inputs for TaskContext info
        taskContext._stageId = read_int(infile)
        taskContext._partitionId = read_int(infile)
        taskContext._attemptNumber = read_int(infile)
        taskContext._taskAttemptId = read_long(infile)
        taskContext._cpus = read_int(infile)
        taskContext._resources = {}
        for r in range(read_int(infile)):
            key = utf8_deserializer.loads(infile)
            name = utf8_deserializer.loads(infile)
            addresses = []
            taskContext._resources = {}
            for a in range(read_int(infile)):
                addresses.append(utf8_deserializer.loads(infile))
            taskContext._resources[key] = ResourceInformation(name, addresses)

        taskContext._localProperties = dict()
        for i in range(read_int(infile)):
            k = utf8_deserializer.loads(infile)
            v = utf8_deserializer.loads(infile)
            taskContext._localProperties[k] = v

        shuffle.MemoryBytesSpilled = 0
        shuffle.DiskBytesSpilled = 0
        _accumulatorRegistry.clear()

        # fetch name of workdir
        spark_files_dir = utf8_deserializer.loads(infile)
        SparkFiles._root_directory = spark_files_dir
        SparkFiles._is_running_on_worker = True

        # fetch names of includes (*.zip and *.egg files) and construct PYTHONPATH
        add_path(spark_files_dir)  # *.py files that were added will be copied here
        num_python_includes = read_int(infile)
        for _ in range(num_python_includes):
            filename = utf8_deserializer.loads(infile)
            add_path(os.path.join(spark_files_dir, filename))

        importlib.invalidate_caches()

        # fetch names and values of broadcast variables
        needs_broadcast_decryption_server = read_bool(infile)
        num_broadcast_variables = read_int(infile)
        if needs_broadcast_decryption_server:
            # read the decrypted data from a server in the jvm
            port = read_int(infile)
            auth_secret = utf8_deserializer.loads(infile)
            (broadcast_sock_file, _) = local_connect_and_auth(port, auth_secret)

        for _ in range(num_broadcast_variables):
            bid = read_long(infile)
            if bid >= 0:
                if needs_broadcast_decryption_server:
                    read_bid = read_long(broadcast_sock_file)
                    assert read_bid == bid
                    _broadcastRegistry[bid] = Broadcast(sock_file=broadcast_sock_file)
                else:
                    path = utf8_deserializer.loads(infile)
                    _broadcastRegistry[bid] = Broadcast(path=path)

            else:
                bid = -bid - 1
                _broadcastRegistry.pop(bid)

        if needs_broadcast_decryption_server:
            broadcast_sock_file.write(b"1")
            broadcast_sock_file.close()

        _accumulatorRegistry.clear()
        eval_type = read_int(infile)
        if eval_type == PythonEvalType.NON_UDF:
            func, profiler, deserializer, serializer = read_command(pickleSer, infile)
        else:
            func, profiler, deserializer, serializer = read_udfs(pickleSer, infile, eval_type)

        init_time = time.time()

        def process():
            iterator = deserializer.load_stream(infile)
            out_iter = func(split_index, iterator)
            try:
                serializer.dump_stream(out_iter, outfile)
            finally:
                if hasattr(out_iter, "close"):
                    out_iter.close()

        if profiler:
            profiler.profile(process)
        else:
            process()

        # Reset task context to None. This is a guard code to avoid residual context when worker
        # reuse.
        TaskContext._setTaskContext(None)
        BarrierTaskContext._setTaskContext(None)
    except BaseException as e:
        try:
            exc_info = None
            if os.environ.get("SPARK_SIMPLIFIED_TRACEBACK", False):
                tb = try_simplify_traceback(sys.exc_info()[-1])
                if tb is not None:
                    e.__cause__ = None
                    exc_info = "".join(traceback.format_exception(type(e), e, tb))
            if exc_info is None:
                exc_info = traceback.format_exc()

            write_int(SpecialLengths.PYTHON_EXCEPTION_THROWN, outfile)
            write_with_length(exc_info.encode("utf-8"), outfile)
        except IOError:
            # JVM close the socket
            pass
        except BaseException:
            # Write the error to stderr if it happened while serializing
            print("PySpark worker failed with exception:", file=sys.stderr)
            print(traceback.format_exc(), file=sys.stderr)
        sys.exit(-1)
    finally:
        if faulthandler_log_path:
            faulthandler.disable()
            faulthandler_log_file.close()
            os.remove(faulthandler_log_path)
    finish_time = time.time()
    report_times(outfile, boot_time, init_time, finish_time)
    write_long(shuffle.MemoryBytesSpilled, outfile)
    write_long(shuffle.DiskBytesSpilled, outfile)

    # Mark the beginning of the accumulators section of the output
    write_int(SpecialLengths.END_OF_DATA_SECTION, outfile)
    write_int(len(_accumulatorRegistry), outfile)
    for (aid, accum) in _accumulatorRegistry.items():
        pickleSer._write_with_length((aid, accum._value), outfile)

    # check end of stream
    if read_int(infile) == SpecialLengths.END_OF_STREAM:
        write_int(SpecialLengths.END_OF_STREAM, outfile)
    else:
        # write a different value to tell JVM to not reuse this worker
        write_int(SpecialLengths.END_OF_DATA_SECTION, outfile)
        sys.exit(-1)


if __name__ == "__main__":
    # Read information about how to connect back to the JVM from the environment.
    java_port = int(os.environ["PYTHON_WORKER_FACTORY_PORT"])
    auth_secret = os.environ["PYTHON_WORKER_FACTORY_SECRET"]
    (sock_file, _) = local_connect_and_auth(java_port, auth_secret)
    # TODO: Remove the following two lines and use `Process.pid()` when we drop JDK 8.
    write_int(os.getpid(), sock_file)
    sock_file.flush()
    main(sock_file, sock_file)