Multithreaded S3 downloads

URIDownloader.py

# pip install smart_open[s3]
from collections import deque
from concurrent.futures import ThreadPoolExecutor as _ThreadPoolExecutor
from functools import partial
from typing import Callable, Dict, Optional, Iterable, Iterator, Sequence

import boto3
import botocore
import smart_open


class URIDownloader:
    """Stream S3 URIs into memory using multithreading."""

    def __init__(self, threads: int = 64):
        self.threads = threads
        self.executor = ThreadPoolExecutor(max_workers=threads)
        config = botocore.client.Config(
            max_pool_connections=threads,
            tcp_keepalive=True,
            retries={"max_attempts": 6, "mode": "adaptive"},
        )
        client = boto3.session.Session().client("s3", config=config)  # thread-safe
        self._open = partial(smart_open.open, transport_params={"client": client})

    def read(self, uri: str, /, mode="rb", **kwargs) -> bytes:
        """Download (and decompress) a URI using smart_open."""
        with self._open(uri, mode, **kwargs) as fp:
            return fp.read()

    def read_multi(self, uris: Iterable[str], **kwargs) -> Iterator[bytes]:
        """Download (and decompress) URIs with a multithreaded boto3 client."""
        yield from self.executor.imap(partial(self.read, **kwargs), uris)

    def read_multi_dict(self, uris: Sequence[str], **kwargs) -> Dict[str, bytes]:
        """Download (and decompress) URIs with a multithreaded boto3 client into a dict[uri, bytes]."""
        return dict(zip(uris, self.read_multi(uris, **kwargs)))


class ThreadPoolExecutor(_ThreadPoolExecutor):
    """The missing ThreadPoolExecutor.imap ref https://gist.github.com/ddelange/c98b05437f80e4b16bf4fc20fde9c999."""

    def imap(self, fn: Callable, *iterables: Iterable, timeout: Optional[float] = None):
        """Ordered imap that lazily consumes iterables."""
        futures, maxlen = deque(), self._max_workers * 3  # two queued tasks per worker
        popleft, append, submit = futures.popleft, futures.append, self.submit

        def get():
            """Block until the next task is done and return the result."""
            return popleft().result(timeout)

        for args in zip(*iterables):
            append(submit(fn, *args))
            if len(futures) == maxlen:
                yield get()

        while futures:
            yield get()

for an asynchronous variant, see https://gist.github.com/ddelange/643fbb791b398783c04d1ceb90102163#file-proxy-py-L28