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, filter_cached, read_cache, write_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         if sys.version_info[:2] >= (3, 7):
  51             all_tasks = asyncio.all_tasks
  52         else:
  53             all_tasks = asyncio.Task.all_tasks
  54         # This part is borrowed from asyncio/runners.py in Python 3.7b2.
  55         to_cancel = [task for task in all_tasks(loop) if not task.done()]
  56         if not to_cancel:
  57             return
  58
  59         for task in to_cancel:
  60             task.cancel()
  61         if sys.version_info >= (3, 7):
  62             loop.run_until_complete(asyncio.gather(*to_cancel, return_exceptions=True))
  63         else:
  64             loop.run_until_complete(
  65                 asyncio.gather(*to_cancel, loop=loop, return_exceptions=True)
  66             )
  67     finally:
  68         # `concurrent.futures.Future` objects cannot be cancelled once they
  69         # are already running. There might be some when the `shutdown()` happened.
  70         # Silence their logger's spew about the event loop being closed.
  71         cf_logger = logging.getLogger("concurrent.futures")
  72         cf_logger.setLevel(logging.CRITICAL)
  73         loop.close()
  74
  75
  76 # diff-shades depends on being to monkeypatch this function to operate. I know it's
  77 # not ideal, but this shouldn't cause any issues ... hopefully. ~ichard26
  78 @mypyc_attr(patchable=True)
  79 def reformat_many(
  80     sources: Set[Path],
  81     fast: bool,
  82     write_back: WriteBack,
  83     mode: Mode,
  84     report: Report,
  85     workers: Optional[int],
  86 ) -> None:
  87     """Reformat multiple files using a ProcessPoolExecutor."""
  88     maybe_install_uvloop()
  89
  90     executor: Executor
  91     if workers is None:
  92         workers = os.cpu_count() or 1
  93     if sys.platform == "win32":
  94         # Work around https://bugs.python.org/issue26903
  95         workers = min(workers, 60)
  96     try:
  97         executor = ProcessPoolExecutor(max_workers=workers)
  98     except (ImportError, NotImplementedError, OSError):
  99         # we arrive here if the underlying system does not support multi-processing
 100         # like in AWS Lambda or Termux, in which case we gracefully fallback to
 101         # a ThreadPoolExecutor with just a single worker (more workers would not do us
 102         # any good due to the Global Interpreter Lock)
 103         executor = ThreadPoolExecutor(max_workers=1)
 104
 105     loop = asyncio.new_event_loop()
 106     asyncio.set_event_loop(loop)
 107     try:
 108         loop.run_until_complete(
 109             schedule_formatting(
 110                 sources=sources,
 111                 fast=fast,
 112                 write_back=write_back,
 113                 mode=mode,
 114                 report=report,
 115                 loop=loop,
 116                 executor=executor,
 117             )
 118         )
 119     finally:
 120         try:
 121             shutdown(loop)
 122         finally:
 123             asyncio.set_event_loop(None)
 124         if executor is not None:
 125             executor.shutdown()
 126
 127
 128 async def schedule_formatting(
 129     sources: Set[Path],
 130     fast: bool,
 131     write_back: WriteBack,
 132     mode: Mode,
 133     report: "Report",
 134     loop: asyncio.AbstractEventLoop,
 135     executor: "Executor",
 136 ) -> None:
 137     """Run formatting of `sources` in parallel using the provided `executor`.
 138
 139     (Use ProcessPoolExecutors for actual parallelism.)
 140
 141     `write_back`, `fast`, and `mode` options are passed to
 142     :func:`format_file_in_place`.
 143     """
 144     cache: Cache = {}
 145     if write_back not in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
 146         cache = read_cache(mode)
 147         sources, cached = filter_cached(cache, sources)
 148         for src in sorted(cached):
 149             report.done(src, Changed.CACHED)
 150     if not sources:
 151         return
 152
 153     cancelled = []
 154     sources_to_cache = []
 155     lock = None
 156     if write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
 157         # For diff output, we need locks to ensure we don't interleave output
 158         # from different processes.
 159         manager = Manager()
 160         lock = manager.Lock()
 161     tasks = {
 162         asyncio.ensure_future(
 163             loop.run_in_executor(
 164                 executor, format_file_in_place, src, fast, mode, write_back, lock
 165             )
 166         ): src
 167         for src in sorted(sources)
 168     }
 169     pending = tasks.keys()
 170     try:
 171         loop.add_signal_handler(signal.SIGINT, cancel, pending)
 172         loop.add_signal_handler(signal.SIGTERM, cancel, pending)
 173     except NotImplementedError:
 174         # There are no good alternatives for these on Windows.
 175         pass
 176     while pending:
 177         done, _ = await asyncio.wait(pending, return_when=asyncio.FIRST_COMPLETED)
 178         for task in done:
 179             src = tasks.pop(task)
 180             if task.cancelled():
 181                 cancelled.append(task)
 182             elif task.exception():
 183                 report.failed(src, str(task.exception()))
 184             else:
 185                 changed = Changed.YES if task.result() else Changed.NO
 186                 # If the file was written back or was successfully checked as
 187                 # well-formatted, store this information in the cache.
 188                 if write_back is WriteBack.YES or (
 189                     write_back is WriteBack.CHECK and changed is Changed.NO
 190                 ):
 191                     sources_to_cache.append(src)
 192                 report.done(src, changed)
 193     if cancelled:
 194         if sys.version_info >= (3, 7):
 195             await asyncio.gather(*cancelled, return_exceptions=True)
 196         else:
 197             await asyncio.gather(*cancelled, loop=loop, return_exceptions=True)
 198     if sources_to_cache:
 199         write_cache(cache, sources_to_cache, mode)