src/black/concurrency.py

   1 """
   2 Formatting many files at once via multiprocessing. Contains entrypoint and utilities.
   3
   4 NOTE: this module is only imported if we need to format several files at once.
   5 """
   6
   7 import asyncio
   8 import logging
   9 import os
  10 import signal
  11 import sys
  12 from concurrent.futures import Executor, ProcessPoolExecutor, ThreadPoolExecutor
  13 from multiprocessing import Manager
  14 from pathlib import Path
  15 from typing import Any, Iterable, Optional, Set
  16
  17 from mypy_extensions import mypyc_attr
  18
  19 from black import WriteBack, format_file_in_place
  20 from black.cache import Cache
  21 from black.mode import Mode
  22 from black.output import err
  23 from black.report import Changed, Report
  24
  25
  26 def maybe_install_uvloop() -> None:
  27     """If our environment has uvloop installed we use it.
  28
  29     This is called only from command-line entry points to avoid
  30     interfering with the parent process if Black is used as a library.
  31     """
  32     try:
  33         import uvloop
  34
  35         uvloop.install()
  36     except ImportError:
  37         pass
  38
  39
  40 def cancel(tasks: Iterable["asyncio.Task[Any]"]) -> None:
  41     """asyncio signal handler that cancels all `tasks` and reports to stderr."""
  42     err("Aborted!")
  43     for task in tasks:
  44         task.cancel()
  45
  46
  47 def shutdown(loop: asyncio.AbstractEventLoop) -> None:
  48     """Cancel all pending tasks on `loop`, wait for them, and close the loop."""
  49     try:
  50         # This part is borrowed from asyncio/runners.py in Python 3.7b2.
  51         to_cancel = [task for task in asyncio.all_tasks(loop) if not task.done()]
  52         if not to_cancel:
  53             return
  54
  55         for task in to_cancel:
  56             task.cancel()
  57         loop.run_until_complete(asyncio.gather(*to_cancel, return_exceptions=True))
  58     finally:
  59         # `concurrent.futures.Future` objects cannot be cancelled once they
  60         # are already running. There might be some when the `shutdown()` happened.
  61         # Silence their logger's spew about the event loop being closed.
  62         cf_logger = logging.getLogger("concurrent.futures")
  63         cf_logger.setLevel(logging.CRITICAL)
  64         loop.close()
  65
  66
  67 # diff-shades depends on being to monkeypatch this function to operate. I know it's
  68 # not ideal, but this shouldn't cause any issues ... hopefully. ~ichard26
  69 @mypyc_attr(patchable=True)
  70 def reformat_many(
  71     sources: Set[Path],
  72     fast: bool,
  73     write_back: WriteBack,
  74     mode: Mode,
  75     report: Report,
  76     workers: Optional[int],
  77 ) -> None:
  78     """Reformat multiple files using a ProcessPoolExecutor."""
  79     maybe_install_uvloop()
  80
  81     executor: Executor
  82     if workers is None:
  83         workers = int(os.environ.get("BLACK_NUM_WORKERS", 0))
  84         workers = workers or os.cpu_count() or 1
  85     if sys.platform == "win32":
  86         # Work around https://bugs.python.org/issue26903
  87         workers = min(workers, 60)
  88     try:
  89         executor = ProcessPoolExecutor(max_workers=workers)
  90     except (ImportError, NotImplementedError, OSError):
  91         # we arrive here if the underlying system does not support multi-processing
  92         # like in AWS Lambda or Termux, in which case we gracefully fallback to
  93         # a ThreadPoolExecutor with just a single worker (more workers would not do us
  94         # any good due to the Global Interpreter Lock)
  95         executor = ThreadPoolExecutor(max_workers=1)
  96
  97     loop = asyncio.new_event_loop()
  98     asyncio.set_event_loop(loop)
  99     try:
 100         loop.run_until_complete(
 101             schedule_formatting(
 102                 sources=sources,
 103                 fast=fast,
 104                 write_back=write_back,
 105                 mode=mode,
 106                 report=report,
 107                 loop=loop,
 108                 executor=executor,
 109             )
 110         )
 111     finally:
 112         try:
 113             shutdown(loop)
 114         finally:
 115             asyncio.set_event_loop(None)
 116         if executor is not None:
 117             executor.shutdown()
 118
 119
 120 async def schedule_formatting(
 121     sources: Set[Path],
 122     fast: bool,
 123     write_back: WriteBack,
 124     mode: Mode,
 125     report: "Report",
 126     loop: asyncio.AbstractEventLoop,
 127     executor: "Executor",
 128 ) -> None:
 129     """Run formatting of `sources` in parallel using the provided `executor`.
 130
 131     (Use ProcessPoolExecutors for actual parallelism.)
 132
 133     `write_back`, `fast`, and `mode` options are passed to
 134     :func:`format_file_in_place`.
 135     """
 136     cache = Cache.read(mode)
 137     if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
 138         sources, cached = cache.filtered_cached(sources)
 139         for src in sorted(cached):
 140             report.done(src, Changed.CACHED)
 141     if not sources:
 142         return
 143
 144     cancelled = []
 145     sources_to_cache = []
 146     lock = None
 147     if write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
 148         # For diff output, we need locks to ensure we don't interleave output
 149         # from different processes.
 150         manager = Manager()
 151         lock = manager.Lock()
 152     tasks = {
 153         asyncio.ensure_future(
 154             loop.run_in_executor(
 155                 executor, format_file_in_place, src, fast, mode, write_back, lock
 156             )
 157         ): src
 158         for src in sorted(sources)
 159     }
 160     pending = tasks.keys()
 161     try:
 162         loop.add_signal_handler(signal.SIGINT, cancel, pending)
 163         loop.add_signal_handler(signal.SIGTERM, cancel, pending)
 164     except NotImplementedError:
 165         # There are no good alternatives for these on Windows.
 166         pass
 167     while pending:
 168         done, _ = await asyncio.wait(pending, return_when=asyncio.FIRST_COMPLETED)
 169         for task in done:
 170             src = tasks.pop(task)
 171             if task.cancelled():
 172                 cancelled.append(task)
 173             elif task.exception():
 174                 report.failed(src, str(task.exception()))
 175             else:
 176                 changed = Changed.YES if task.result() else Changed.NO
 177                 # If the file was written back or was successfully checked as
 178                 # well-formatted, store this information in the cache.
 179                 if write_back is WriteBack.YES or (
 180                     write_back is WriteBack.CHECK and changed is Changed.NO
 181                 ):
 182                     sources_to_cache.append(src)
 183                 report.done(src, changed)
 184     if cancelled:
 185         await asyncio.gather(*cancelled, return_exceptions=True)
 186     if sources_to_cache:
 187         cache.write(sources_to_cache)