Issue #7242: On Solaris 9 and earlier calling os.fork() from within a

thread could raise an incorrect RuntimeError about not holding the import
lock.  The import lock is now reinitialized after fork.

Lib/test/test_thread.py

@@ -4,6 +4,7 @@ import random
 from test import test_support
 import thread
 import time
+import sys
 import weakref
 
 from test import lock_tests
@@ -196,8 +197,47 @@ class LockTests(lock_tests.LockTests):
     locktype = thread.allocate_lock
 
 
+class TestForkInThread(unittest.TestCase):
+    def setUp(self):
+        self.read_fd, self.write_fd = os.pipe()
+
+    def test_forkinthread(self):
+        if sys.platform.startswith('win'):
+            from test.test_support import TestSkipped
+            raise TestSkipped("This test is only appropriate for "
+                              "POSIX-like systems.")
+        def thread1():
+            try:
+                pid = os.fork() # fork in a thread
+            except RuntimeError:
+                sys.exit(0) # exit the child
+
+            if pid == 0: # child
+                os.close(self.read_fd)
+                os.write(self.write_fd, "OK")
+                sys.exit(0)
+            else: # parent
+                os.close(self.write_fd)
+
+        thread.start_new_thread(thread1, ())
+        self.assertEqual(os.read(self.read_fd, 2), "OK",
+                         "Unable to fork() in thread")
+
+    def tearDown(self):
+        try:
+            os.close(self.read_fd)
+        except OSError:
+            pass
+
+        try:
+            os.close(self.write_fd)
+        except OSError:
+            pass
+
+
 def test_main():
-    test_support.run_unittest(ThreadRunningTests, BarrierTest, LockTests)
+    test_support.run_unittest(ThreadRunningTests, BarrierTest, LockTests,
+                              TestForkInThread)
 
 if __name__ == "__main__":
     test_main()

Misc/NEWS

@@ -87,6 +87,10 @@ Extension Modules
 - Stop providing crtassem.h symbols when compiling with Visual Studio 2010, as
   msvcr100.dll is not a platform assembly anymore.
 
+- Issue #7242: On Solaris 9 and earlier calling os.fork() from within a
+  thread could raise an incorrect RuntimeError about not holding the import
+  lock.  The import lock is now reinitialized after fork.
+
 Tests
 -----
 

Modules/posixmodule.c

@@ -3605,14 +3605,18 @@ static PyObject *
 posix_fork1(PyObject *self, PyObject *noargs)
 {
 	pid_t pid;
-	int result;
+	int result = 0;
 	_PyImport_AcquireLock();
 	pid = fork1();
-	result = _PyImport_ReleaseLock();
+	if (pid == 0) {
+		/* child: this clobbers and resets the import lock. */
+		PyOS_AfterFork();
+	} else {
+		/* parent: release the import lock. */
+		result = _PyImport_ReleaseLock();
+	}
 	if (pid == -1)
 		return posix_error();
-	if (pid == 0)
-		PyOS_AfterFork();
 	if (result < 0) {
 		/* Don't clobber the OSError if the fork failed. */
 		PyErr_SetString(PyExc_RuntimeError,
@@ -3634,14 +3638,18 @@ static PyObject *
 posix_fork(PyObject *self, PyObject *noargs)
 {
 	pid_t pid;
-	int result;
+	int result = 0;
 	_PyImport_AcquireLock();
 	pid = fork();
-	result = _PyImport_ReleaseLock();
+	if (pid == 0) {
+		/* child: this clobbers and resets the import lock. */
+		PyOS_AfterFork();
+	} else {
+		/* parent: release the import lock. */
+		result = _PyImport_ReleaseLock();
+	}
 	if (pid == -1)
 		return posix_error();
-	if (pid == 0)
-		PyOS_AfterFork();
 	if (result < 0) {
 		/* Don't clobber the OSError if the fork failed. */
 		PyErr_SetString(PyExc_RuntimeError,
@@ -3759,11 +3767,12 @@ posix_forkpty(PyObject *self, PyObject *noargs)
 
 	_PyImport_AcquireLock();
 	pid = forkpty(&master_fd, NULL, NULL, NULL);
+	if (pid == 0)
+		PyOS_AfterFork();
+
 	result = _PyImport_ReleaseLock();
 	if (pid == -1)
 		return posix_error();
-	if (pid == 0)
-		PyOS_AfterFork();
 	if (result < 0) {
 		/* Don't clobber the OSError if the fork failed. */
 		PyErr_SetString(PyExc_RuntimeError,

Python/import.c

@@ -301,14 +301,18 @@ _PyImport_ReleaseLock(void)
 	return 1;
 }
 
-/* This function used to be called from PyOS_AfterFork to ensure that newly
-   created child processes do not share locks with the parent, but for some
-   reason only on AIX systems. Instead of re-initializing the lock, we now
-   acquire the import lock around fork() calls. */
+/* This function is called from PyOS_AfterFork to ensure that newly
+   created child processes do not share locks with the parent.
+   We now acquire the import lock around fork() calls but on some platforms
+   (Solaris 9 and earlier? see isue7242) that still left us with problems. */
 
 void
 _PyImport_ReInitLock(void)
 {
+ 	if (import_lock != NULL)
+ 		import_lock = PyThread_allocate_lock();
+ 	import_lock_thread = -1;
+ 	import_lock_level = 0;
 }
 
 #endif