[WIP] bpo-38546: Add support.get_child_processes()

Lib/test/libregrtest/runtest.py

@@ -226,6 +226,9 @@ def _runtest_inner2(ns, test_name):
     if test_runner is None:
         test_runner = functools.partial(_test_module, the_module)
 
+    pid = os.getpid()
+    nchild_before = support.get_child_processes(pid)
+
     try:
         if ns.huntrleaks:
             # Return True if the test leaked references
@@ -249,6 +252,16 @@ def _runtest_inner2(ns, test_name):
         gc.garbage.clear()
 
     support.reap_children()
+    if nchild_before is not None:
+        nchild_after = support.get_child_processes(pid)
+        diff = len(nchild_after) - len(nchild_before)
+        if diff:
+            print(f"Warning -- {test_name} leaked "
+                  f"{diff} child processes: "
+                  f"created={nchild_after - nchild_before}, "
+                  f"completed={nchild_before - nchild_after}",
+                  file=sys.stderr)
+            support.environment_altered = True
 
     return refleak
 

Lib/test/support/__init__.py

@@ -3403,3 +3403,38 @@ def __exit__(self, *exc_info):
         del self.exc_value
         del self.exc_traceback
         del self.thread
+
+
+def get_child_processes(ppid):
+    """
+    Get directly child processes of parent process identifier 'pid'.
+    """
+    proc_dir = '/proc'
+    try:
+        names = os.listdir(proc_dir)
+    except FileNotFoundError:
+        return None
+
+    children = []
+    for name in names:
+        if not name.isdigit():
+            continue
+        pid = int(name)
+
+        filename = os.path.join(proc_dir, str(pid), 'status')
+        try:
+            fp = open(filename, encoding="utf-8")
+        except FileNotFoundError:
+            # process completed: ignore it
+            continue
+
+        proc_ppid = None
+        with fp:
+            for line in fp:
+                if line.startswith('PPid:'):
+                    proc_ppid = int(line[5:].strip())
+                    break
+        if proc_ppid == ppid:
+            children.append(pid)
+
+    return set(children)