[RFC v2 01/16] bitbake: fork: Add os.fork() wrappers

[Joshua Watt <jpewhacker@gmail.com>]

Adds a compatibility wrapper around os.fork() that backports the ability
to register fork event handlers (os.register_at_fork()) from Python 3.7

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
---
 bitbake/bin/bitbake-worker |  2 +-
 bitbake/lib/bb/fork.py     | 71 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 bitbake/lib/bb/fork.py

diff --git a/bitbake/bin/bitbake-worker b/bitbake/bin/bitbake-worker
index e925054b7f9..baa1a84e6dd 100755
--- a/bitbake/bin/bitbake-worker
+++ b/bitbake/bin/bitbake-worker
@@ -181,7 +181,7 @@ def fork_off_task(cfg, data, databuilder, workerdata, fn, task, taskname, append
         pipein, pipeout = os.pipe()
         pipein = os.fdopen(pipein, 'rb', 4096)
         pipeout = os.fdopen(pipeout, 'wb', 0)
-        pid = os.fork()
+        pid = bb.fork.fork()
     except OSError as e:
         logger.critical("fork failed: %d (%s)" % (e.errno, e.strerror))
         sys.exit(1)
diff --git a/bitbake/lib/bb/fork.py b/bitbake/lib/bb/fork.py
new file mode 100644
index 00000000000..5ac5aba1832
--- /dev/null
+++ b/bitbake/lib/bb/fork.py
@@ -0,0 +1,71 @@
+# ex:ts=4:sw=4:sts=4:et
+# -*- tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*-
+#
+# Copyright (C) 2018 Garmin Ltd.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+#
+"""
+Python wrappers for os.fork() that allow the insertion of callbacks for fork events.
+This is designed to exacmimic os.register_at_fork() available in Python 3.7 with the
+intent that it can be removed when that version becomes standard
+"""
+
+import sys
+import os
+
+before_calls = []
+after_in_parent_calls = []
+after_in_child_calls = []
+
+def _do_calls(l, reverse=False):
+    # Make a copy in case the list is modified in the callback
+    copy = l[:]
+    if reverse:
+        copy = reversed(copy)
+
+    for f in copy:
+        # All exception in calls are ignored
+        try:
+            f()
+        except:
+            pass
+
+def fork():
+    if sys.hexversion >= 0x030700F0:
+        return os.fork()
+
+    _do_calls(before_calls, reverse=True)
+
+    ret = os.fork()
+    if ret == 0:
+        _do_calls(after_in_child_calls)
+    else:
+        _do_calls(after_in_parent_calls)
+    return ret
+
+def register_at_fork(*, before=None, after_in_parent=None, after_in_child=None):
+    if sys.hexversion >= 0x030700F0:
+        os.register_at_fork(before=before, after_in_parent=after_in_parent, after_in_child=after_in_child)
+        return
+
+    if before is not None:
+        before_calls.append(before)
+
+    if after_in_parent is not None:
+        after_in_parent_calls.append(after_in_parent)
+
+    if after_in_child is not None:
+        after_in_child_calls.append(after_in_child)
+
-- 
2.17.1