#!/usr/bin/env python3fromconcurrent.futuresimportThreadPoolExecutor,waitfromsubprocessimportPopendeftarget(i):p=Popen(['touch',f'/tmp/reproc-{i}'])p.communicate()executor=ThreadPoolExecutor(max_workers=64)futures=set()foriinrange(10_000):futures.add(executor.submit(target,i))wait(futures)

real    0m2.419suser    0m4.524ssys     0m0.976s

real    0m11.772suser    0m10.287ssys     0m14.409s

diff --git a/Modules/_posixsubprocess.c b/Modules/_posixsubprocess.cindex 2898eedc3e..fb6c235901 100644--- a/Modules/_posixsubprocess.c+++ b/Modules/_posixsubprocess.c@@ -889,7 +889,7 @@ do_fork_exec(char *const exec_array[],         /* These are checked by our caller; verify them in debug builds. */         assert(uid == (uid_t)-1);         assert(gid == (gid_t)-1);-        assert(extra_group_size < 0);+        assert(extra_group_size == 0);         assert(preexec_fn == Py_None);         /* Drop the GIL so that other threads can continue execution while this@@ -1208,7 +1208,7 @@ subprocess_fork_exec_impl(PyObject *module, PyObject *process_args,     /* Use vfork() only if it's safe. See the comment above child_exec(). */     sigset_t old_sigs;     if (preexec_fn == Py_None && allow_vfork &&-        uid == (uid_t)-1 && gid == (gid_t)-1 && extra_group_size < 0) {+        uid == (uid_t)-1 && gid == (gid_t)-1 && extra_group_size == 0) {         /* Block all signals to ensure that no signal handlers are run in the          * child process while it shares memory with us. Note that signals          * used internally by C libraries won't be blocked by

extra_group_size=PySequence_Size(extra_groups_packed);if (extra_group_size<0)    gotocleanup;