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: 15d7448e04aa78c827d2cef9eb1a62bd6e0dd119)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Martin Jansa <martin.jansa@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 cdec9e4d6c..f59c2515b7 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 a66117acad..953c02ef3e 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 6fce19b464..778cbb5897 100644
--- a/bitbake/lib/bb/cooker.py
+++ b/bitbake/lib/bb/cooker.py
@@ -12,7 +12,7 @@
 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 76b189291d..34b3a2ae9d 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 d2f11e4377..1b4fb93a30 100644
--- a/bitbake/lib/bb/utils.py
+++ b/bitbake/lib/bb/utils.py
@@ -14,7 +14,7 @@ import logging
 import bb
 import bb.msg
 import locale
-import multiprocessing
+from bb import multiprocessing
 import fcntl
 import importlib
 import importlib.machinery
@@ -1174,8 +1174,6 @@ 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 5349cd5867..ed1ade749c 100644
--- a/bitbake/lib/hashserv/tests.py
+++ b/bitbake/lib/hashserv/tests.py
@@ -11,7 +11,7 @@ from bb.asyncrpc import InvokeError
 from .client import ClientPool
 import hashlib
 import logging
-import multiprocessing
+from bb import multiprocessing
 import os
 import sys
 import tempfile