Revert (unneeded, already done elsewhere) "gh-98552: flush std streams in the multiprocessing forkserver before fork (#141849)"
This reverts commit 58badb1711.
* gh-138813: Default `BaseProcess` `kwargs` to `None` (#138814)
Set `BaseProcess.__init__(..., kwargs=None)` and initialize `kwargs` with
`dict(kwargs) if kwargs else {}`. This avoids a shared mutable default and
matches threading.Thread behavior.
Co-authored-by: Dmitrii Chuprov <cheese@altlinux.org>
* DummyProcess kwargs=None (which threading.Thread accepts properly)
Co-authored-by: Gregory P. Smith <greg@krypto.org>
gh-126631: gh-137996: fix pre-loading of `__main__`
The `main_path` parameter was renamed `init_main_from_name`, update the
forkserver code accordingly. This was leading to slower startup times when people
were trying to preload the main module.
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Co-authored-by: Gregory P. Smith <greg@krypto.org>
fix potential hang.
It can happen that the child crashes right in the beginning for whatever reason. In this case, the parent will hang when writing into the pipe, because the child fd is not closed yet.
The normal pattern is to close the child fds right after the child proc is forked/executed/spawned, so when the child dies, then also the pipes will be closed, and there will be no hang (the parent gets SIGPIPE instead).
If a preloaded module writes to stdout or stderr, and the stream is buffered,
child processes will inherit the buffered data after forking. Attempt to
prevent this by flushing the streams after preload.
Co-authored-by: Mikhail Efimov <efimov.mikhail@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>
Doc/library/multiprocessing.rst: freeze_support: Change to specify spawn method instead of platform
Have multiprocessing.freeze_support() enable on spawn, not just win32.
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Co-authored-by: Gregory P. Smith <greg@krypto.org>
The SyncManager provided support for various data structures such as dict, list, and queue, but oddly, not set.
This introduces support for set by defining SetProxy and registering it with SyncManager.
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Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
Correct pthread_sigmask in resource_tracker to restore old signals
Using SIG_UNBLOCK to remove blocked "ignored signals" may accidentally
cause side effects if the calling parent already had said signals
blocked to begin with and did not intend to unblock them when
creating a pool. Use SIG_SETMASK instead with the previous mask of
blocked signals to restore the original blocked set.
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
* Correct pthread_sigmask in resource_tracker to restore old signals
Using SIG_UNBLOCK to remove blocked "ignored signals" may accidentally
cause side effects if the calling parent already had said signals
blocked to begin with and did not intend to unblock them when
creating a pool. Use SIG_SETMASK instead with the previous mask of
blocked signals to restore the original blocked set.
* Adding resource_tracker blocked signals test
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
This adds authentication to the forkserver control socket. In the past only filesystem permissions protected this socket from code injection into the forkserver process by limiting access to the same UID, which didn't exist when Linux abstract namespace sockets were used (see issue) meaning that any process in the same system network namespace could inject code. We've since stopped using abstract namespace sockets by default, but protecting our control sockets regardless of type is a good idea.
This reuses the HMAC based shared key auth already used by `multiprocessing.connection` sockets for other purposes.
Doing this is useful so that filesystem permissions are not relied upon and trust isn't implied by default between all processes running as the same UID with access to the unix socket.
### pyperformance benchmarks
No significant changes. Including `concurrent_imap` which exercises `multiprocessing.Pool.imap` in that suite.
### Microbenchmarks
This does _slightly_ slow down forkserver use. How much so appears to depend on the platform. Modern platforms and simple platforms are less impacted. This PR adds additional IPC round trips to the control socket to tell forkserver to spawn a new process. Systems with potentially high latency IPC are naturally impacted more.
Typically a 1-4% slowdown on a very targeted process creation microbenchmark, with a worst case overloaded system slowdown of 20%. No evidence that these slowdowns appear in practical sense. See the PR for details.
* gh-71936: Fix race condition in multiprocessing.Pool
Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it
will call BaseProxy._decref() when it is GCed. This may cause a race condition
with Pool(maxtasksperchild=None) on Windows.
A connection would be closed and raised TypeError when a GC occurs between
_ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in
_ConnectionBase.send() in the second or later task, and a new object
is allocated that shares the id() of a previously deleted one.
Instead of using the id() of the token (or the proxy), use a unique,
non-reusable number.
Co-Authored-By: Akinori Hattori <hattya@gmail.com>
gh-117378: Fix multiprocessing forkserver preload sys.path inheritance.
`sys.path` was not properly being sent from the parent process when launching
the multiprocessing forkserver process to preload imports. This bug has been
there since the forkserver start method was introduced in Python 3.4. It was
always _supposed_ to inherit `sys.path` the same way the spawn method does.
Observable behavior change: A `''` value in `sys.path` will now be replaced in
the forkserver's `sys.path` with an absolute pathname
`os.path.abspath(os.getcwd())` saved at the time that `multiprocessing` was
imported in the parent process as it already was when using the spawn start
method. **This will only be observable during forkserver preload imports**.
The code invoked before calling things in another process already correctly sets `sys.path`.
Which is likely why this went unnoticed for so long as a mere performance issue in
some configurations.
A workaround for the bug on impacted Pythons is to set PYTHONPATH in the
environment before multiprocessing's forkserver process was started. Not perfect
as that is then inherited by other children, etc, but likely good enough for many
people's purposes.
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Change the default multiprocessing start method away from fork to forkserver or spawn on the remaining platforms where it was fork. See the issue for context. This makes the default far more thread safe (other than for people spawning threads at import time... - don't do that!).
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>
See https://github.com/python/cpython/issues/121313 for analysis, but this greatly reduces memory overallocation and overhead when multiprocessing is sending non-small data over its pipes between processes.
This flag was added as an escape hatch in gh-91401 and backported to
Python 3.10. The flag broke at some point between its addition and now.
As there is currently no publicly known environments that require this,
remove it rather than work on fixing it.
This leaves the flag in the subprocess module to not break code which
may have used / checked the flag itself.
discussion: https://discuss.python.org/t/subprocess-use-vfork-escape-hatch-broken-fix-or-remove/56915/2
Make error message for index() methods consistent
Remove the repr of the searched value (which can be arbitrary large)
from ValueError messages for list.index(), range.index(), deque.index(),
deque.remove() and ShareableList.index(). Make the error messages
consistent with error messages for other index() and remove()
methods.
Tools such as ruff can ignore "imported but unused" warnings if a
line ends with "# noqa: F401". It avoids the temptation to remove
an import which is used effectively.
AN Long