bitbake: Use a "fork" multiprocessing context

Python 3.14 changes the default multiprocessing context from "fork" to
"forkserver"; however bitbake heavily relies on "fork" to efficiently
pass data to the child processes. As such, make "fork" context in the bb
namespace and use it in place of the normal multiprocessing module.

Note that multiprocessing contexts were added in Python 3.4, so this
should be safe to use even before Python 3.14

[YOCTO #15858]

(Bitbake rev: 0d9d8d0863e82e986c33c08064ce9a99224a06d5)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

7 files changed, 35 insertions, 9 deletions

diff --git a/bitbake/lib/bb/__init__.py b/bitbake/lib/bb/__init__.py
index 5668355737..605355e1ad 100644
--- a/bitbake/lib/bb/__init__.py
+++ b/bitbake/lib/bb/__init__.py
@@ -37,6 +37,34 @@ class BBHandledException(Exception):
 import os
 import logging
 from collections import namedtuple
+import multiprocessing as mp
+
+# Python 3.14 changes the default multiprocessing context from "fork" to
+# "forkserver". However, bitbake heavily relies on "fork" behavior to
+# efficiently pass data to the child processes. Places that need this should do:
+#   from bb import multiprocessing
+# in place of
+#   import multiprocessing
+
+class MultiprocessingContext(object):
+    """
+    Multiprocessing proxy object that uses the "fork" context for a property if
+    available, otherwise goes to the main multiprocessing module. This allows
+    it to be a drop-in replacement for the multiprocessing module, but use the
+    fork context
+    """
+    def __init__(self):
+        super().__setattr__("_ctx", mp.get_context("fork"))
+
+    def __getattr__(self, name):
+        if hasattr(self._ctx, name):
+            return getattr(self._ctx, name)
+        return getattr(mp, name)
+
+    def __setattr__(self, name, value):
+        raise AttributeError(f"Unable to set attribute {name}")
+
+multiprocessing = MultiprocessingContext()
 
 
 class NullHandler(logging.Handler):
diff --git a/bitbake/lib/bb/asyncrpc/serv.py b/bitbake/lib/bb/asyncrpc/serv.py
index 667217c5c1..acdcaf08ed 100644
--- a/bitbake/lib/bb/asyncrpc/serv.py
+++ b/bitbake/lib/bb/asyncrpc/serv.py
@@ -11,7 +11,7 @@ import os
 import signal
 import socket
 import sys
-import multiprocessing
+from bb import multiprocessing
 import logging
 from .connection import StreamConnection, WebsocketConnection
 from .exceptions import ClientError, ServerError, ConnectionClosedError, InvokeError
diff --git a/bitbake/lib/bb/cooker.py b/bitbake/lib/bb/cooker.py
index 1810bcc604..36659cee26 100644
--- a/bitbake/lib/bb/cooker.py
+++ b/bitbake/lib/bb/cooker.py
@@ -12,7 +12,7 @@ import enum
 import sys, os, glob, os.path, re, time
 import itertools
 import logging
-import multiprocessing
+from bb import multiprocessing
 import threading
 from io import StringIO, UnsupportedOperation
 from contextlib import closing
diff --git a/bitbake/lib/bb/server/process.py b/bitbake/lib/bb/server/process.py
index 4b35be62cd..f74b3f1bf2 100644
--- a/bitbake/lib/bb/server/process.py
+++ b/bitbake/lib/bb/server/process.py
@@ -13,7 +13,7 @@
 import bb
 import bb.event
 import logging
-import multiprocessing
+from bb import multiprocessing
 import threading
 import array
 import os
diff --git a/bitbake/lib/bb/tests/support/httpserver.py b/bitbake/lib/bb/tests/support/httpserver.py
index 78f7660053..03327e923b 100644
--- a/bitbake/lib/bb/tests/support/httpserver.py
+++ b/bitbake/lib/bb/tests/support/httpserver.py
@@ -3,7 +3,7 @@
 #
 
 import http.server
-import multiprocessing
+from bb import multiprocessing
 import os
 import traceback
 import signal
@@ -43,7 +43,7 @@ class HTTPService(object):
         self.process = multiprocessing.Process(target=self.server.server_start, args=[self.root_dir, self.logger])
 
         # The signal handler from testimage.bbclass can cause deadlocks here
-        # if the HTTPServer is terminated before it can restore the standard 
+        # if the HTTPServer is terminated before it can restore the standard
         #signal behaviour
         orig = signal.getsignal(signal.SIGTERM)
         signal.signal(signal.SIGTERM, signal.SIG_DFL)
diff --git a/bitbake/lib/bb/utils.py b/bitbake/lib/bb/utils.py
index 0832422683..694e79f552 100644
--- a/bitbake/lib/bb/utils.py
+++ b/bitbake/lib/bb/utils.py
@@ -12,7 +12,7 @@ import sys
 import errno
 import logging
 import locale
-import multiprocessing
+from bb import multiprocessing
 import importlib
 import importlib.machinery
 import importlib.util
@@ -1198,8 +1198,6 @@ def process_profilelog(fn, pout = None):
 #
 def multiprocessingpool(*args, **kwargs):
 
-    import multiprocessing.pool
-    #import multiprocessing.util
     #multiprocessing.util.log_to_stderr(10)
     # Deal with a multiprocessing bug where signals to the processes would be delayed until the work
     # completes. Putting in a timeout means the signals (like SIGINT/SIGTERM) get processed.
diff --git a/bitbake/lib/hashserv/tests.py b/bitbake/lib/hashserv/tests.py
index da3f8e0884..124d8aa005 100644
--- a/bitbake/lib/hashserv/tests.py
+++ b/bitbake/lib/hashserv/tests.py
@@ -10,7 +10,7 @@ from .server import DEFAULT_ANON_PERMS, ALL_PERMISSIONS
 from bb.asyncrpc import InvokeError
 import hashlib
 import logging
-import multiprocessing
+from bb import multiprocessing
 import os
 import sys
 import tempfile