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# Ideally, we would manage async access to stdin/stdout/stderr *without* | |
# setting them to non-blocking mode, because that can break other processes. | |
# (See https://github.com/python-trio/trio/issues/174 for much more detail.) | |
# Of course we can call read/write in a separate thread, but then we lose | |
# cancellation support. | |
# This file demonstrates a weird hack to make blocking read/write cancellable, | |
# and thus at least theoretically possible to integrate into Trio as ordinary | |
# first-class operations. | |
# I blame @geofft. | |
# This only works on Linux; possibly it only works on glibc. | |
import trio | |
import os | |
import socket | |
import errno | |
bad_socket = socket.socket() | |
class BlockingReadTimeoutError(Exception): | |
pass | |
async def blocking_read_with_timeout(fd, count, timeout): | |
print("reading from fd", fd) | |
cancel_requested = False | |
async def kill_it_after_timeout(new_fd): | |
print("sleeping") | |
await trio.sleep(timeout) | |
print("breaking the fd") | |
os.dup2(bad_socket.fileno(), new_fd, inheritable=False) | |
# MAGIC | |
print("setuid(getuid())") | |
os.setuid(os.getuid()) | |
nonlocal cancel_requested | |
cancel_requested = True | |
new_fd = os.dup(fd) | |
print("working fd is", new_fd) | |
try: | |
async with trio.open_nursery() as nursery: | |
nursery.start_soon(kill_it_after_timeout, new_fd) | |
try: | |
data = await trio.run_sync_in_worker_thread(os.read, new_fd, count) | |
except OSError as exc: | |
if cancel_requested and exc.errno == errno.ENOTCONN: | |
# Call was successfully cancelled. In a real version we'd | |
# integrate properly with trio's cancellation tools; here | |
# we'll just raise an arbitrary error. | |
raise BlockingReadTimeoutError from None | |
print("got", data) | |
nursery.cancel_scope.cancel() | |
return data | |
finally: | |
os.close(new_fd) | |
trio.run(blocking_read_with_timeout, 0, 10, 2) |
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