Issue #9573: os.fork now works when triggered as a side effect of import (the wisdom of actually relying on this remains questionable!)
diff --git a/Lib/test/test_fork1.py b/Lib/test/test_fork1.py
index bf7fdcd..8192c38 100644
--- a/Lib/test/test_fork1.py
+++ b/Lib/test/test_fork1.py
@@ -8,13 +8,14 @@
import time
from test.fork_wait import ForkWait
-from test.support import run_unittest, reap_children, get_attribute, import_module
+from test.support import (run_unittest, reap_children, get_attribute,
+ import_module, verbose)
+
threading = import_module('threading')
# Skip test if fork does not exist.
get_attribute(os, 'fork')
-
class ForkTest(ForkWait):
def wait_impl(self, cpid):
for i in range(10):
@@ -28,7 +29,8 @@
self.assertEqual(spid, cpid)
self.assertEqual(status, 0, "cause = %d, exit = %d" % (status&0xff, status>>8))
- def test_import_lock_fork(self):
+ def test_threaded_import_lock_fork(self):
+ """Check fork() in main thread works while a subthread is doing an import"""
import_started = threading.Event()
fake_module_name = "fake test module"
partial_module = "partial"
@@ -45,11 +47,16 @@
import_started.wait()
pid = os.fork()
try:
+ # PyOS_BeforeFork should have waited for the import to complete
+ # before forking, so the child can recreate the import lock
+ # correctly, but also won't see a partially initialised module
if not pid:
m = __import__(fake_module_name)
if m == complete_module:
os._exit(0)
else:
+ if verbose > 1:
+ print("Child encountered partial module")
os._exit(1)
else:
t.join()
@@ -63,6 +70,39 @@
except OSError:
pass
+
+ def test_nested_import_lock_fork(self):
+ """Check fork() in main thread works while the main thread is doing an import"""
+ # Issue 9573: this used to trigger RuntimeError in the child process
+ def fork_with_import_lock(level):
+ release = 0
+ in_child = False
+ try:
+ try:
+ for i in range(level):
+ imp.acquire_lock()
+ release += 1
+ pid = os.fork()
+ in_child = not pid
+ finally:
+ for i in range(release):
+ imp.release_lock()
+ except RuntimeError:
+ if in_child:
+ if verbose > 1:
+ print("RuntimeError in child")
+ os._exit(1)
+ raise
+ if in_child:
+ os._exit(0)
+ self.wait_impl(pid)
+
+ # Check this works with various levels of nested
+ # import in the main thread
+ for level in range(5):
+ fork_with_import_lock(level)
+
+
def test_main():
run_unittest(ForkTest)
reap_children()
diff --git a/Misc/NEWS b/Misc/NEWS
index adec2df..b2c8258 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -46,6 +46,9 @@
Library
-------
+- Issue #9573: os.fork() now works correctly when triggered as a side effect
+ of a module import
+
- Issue #10464: netrc now correctly handles lines with embedded '#' characters.
- Added itertools.accumulate().
diff --git a/Python/import.c b/Python/import.c
index 67c4f70..e582a27 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -325,8 +325,17 @@
{
if (import_lock != NULL)
import_lock = PyThread_allocate_lock();
- import_lock_thread = -1;
- import_lock_level = 0;
+ if (import_lock_level > 1) {
+ /* Forked as a side effect of import */
+ long me = PyThread_get_thread_ident();
+ PyThread_acquire_lock(import_lock, 0);
+ /* XXX: can the previous line fail? */
+ import_lock_thread = me;
+ import_lock_level--;
+ } else {
+ import_lock_thread = -1;
+ import_lock_level = 0;
+ }
}
#endif