From 00468907dca964b94115014360904b5688efbb57 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 14:26:17 -0400
Subject: [PATCH 01/34] os.path.exists("/proc/self/maps") is very expensive,
 maybe because it needs to create and then check a long list of things in
 /proc/self?

---
 threadpoolctl.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index b8b4448d..acbfe245 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -56,6 +56,8 @@
 _SYSTEM_UINT = ctypes.c_uint64 if sys.maxsize > 2**32 else ctypes.c_uint32
 _SYSTEM_UINT_HALF = ctypes.c_uint32 if sys.maxsize > 2**32 else ctypes.c_uint16
 
+_PROCFS_EXISTS = sys.platform == "linux" and os.path.exists("/proc/self")
+
 
 class _dl_phdr_info(ctypes.Structure):
     _fields_ = [
@@ -1137,7 +1139,7 @@ def _load_libraries(self):
                 # CPython before 3.14 does not provide dll inspection.
                 dllist = None
 
-        if sys.platform == "linux" and os.path.exists("/proc/self/maps"):
+        if _PROCFS_EXISTS:
             # On glibc, dl_iterate_phdr has an internal lock, and that plus
             # calling back into Python and the need to (re)acquire the GIL
             # results in deadlocks. To avoid that, use a Linux-specific

From 735a373602c5a5c9083a97aac74cad63c4949873 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 14:30:10 -0400
Subject: [PATCH 02/34] Don't check the existence of the same file repeatedly.

---
 threadpoolctl.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index acbfe245..6ae2e594 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1175,6 +1175,8 @@ def _find_libraries_with_linux(self):
             if start_index == -1 or ".so" not in line:
                 continue
             filepath = line[start_index:]
+            if filepath in filepaths:
+                continue
             if os.path.exists(filepath):
                 filepaths.add(filepath)
 

From 561b60afe35619a912d8c09e52f47e6f709d5bf8 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 14:41:33 -0400
Subject: [PATCH 03/34] Use a regex

---
 threadpoolctl.py | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 6ae2e594..38d5179b 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1161,6 +1161,8 @@ def _load_libraries(self):
             # Non-Linux Unix platforms.
             self._find_libraries_with_dl_iterate_phdr()
 
+    _PATH_RE = re.compile(r" (/[^\n]+\.so[^\n]*)\n", re.MULTILINE)
+
     def _find_libraries_with_linux(self):
         """Loop through loaded libraries and return binders on supported ones
 
@@ -1169,19 +1171,10 @@ def _find_libraries_with_linux(self):
         """
         with open("/proc/self/maps") as f:
             maps = f.read()
-        filepaths = set()
-        for line in maps.splitlines():
-            start_index = line.find("/")
-            if start_index == -1 or ".so" not in line:
-                continue
-            filepath = line[start_index:]
-            if filepath in filepaths:
-                continue
-            if os.path.exists(filepath):
-                filepaths.add(filepath)
-
+        filepaths = set(self._PATH_RE.findall(maps))
         for filepath in filepaths:
-            self._make_controller_from_path(filepath)
+            if os.path.exists(filepath):
+                self._make_controller_from_path(filepath)
 
     def _find_libraries_with_python(self, dllist):
         """Loop through loaded libraries and return binders on supported ones

From b08b5acc531b7af26a3d88857ff08c12115640c7 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 14:42:07 -0400
Subject: [PATCH 04/34] Bytes regex is slightly faster.

---
 threadpoolctl.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 38d5179b..23a9782d 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1161,7 +1161,7 @@ def _load_libraries(self):
             # Non-Linux Unix platforms.
             self._find_libraries_with_dl_iterate_phdr()
 
-    _PATH_RE = re.compile(r" (/[^\n]+\.so[^\n]*)\n", re.MULTILINE)
+    _PATH_RE = re.compile(rb" (/[^\n]+\.so[^\n]*)\n", re.MULTILINE)
 
     def _find_libraries_with_linux(self):
         """Loop through loaded libraries and return binders on supported ones
@@ -1169,10 +1169,11 @@ def _find_libraries_with_linux(self):
         Uses a Linux-specific mechanism:
         https://man7.org/linux/man-pages/man5/proc_pid_maps.5.html
         """
-        with open("/proc/self/maps") as f:
+        with open("/proc/self/maps", "rb") as f:
             maps = f.read()
         filepaths = set(self._PATH_RE.findall(maps))
         for filepath in filepaths:
+            filepath = filepath.decode("utf-8")
             if os.path.exists(filepath):
                 self._make_controller_from_path(filepath)
 

From 2f29ebf3db5deeaf8a33e7de7ff86d954116a79d Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 15:51:27 -0400
Subject: [PATCH 05/34] More robust regex

---
 threadpoolctl.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 23a9782d..a8b12ab4 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1161,7 +1161,7 @@ def _load_libraries(self):
             # Non-Linux Unix platforms.
             self._find_libraries_with_dl_iterate_phdr()
 
-    _PATH_RE = re.compile(rb" (/[^\n]+\.so[^\n]*)\n", re.MULTILINE)
+    _PATH_RE = re.compile(rb" (/[^\n]+\.so[^\n^/]*)\n", re.MULTILINE)
 
     def _find_libraries_with_linux(self):
         """Loop through loaded libraries and return binders on supported ones

From b574c5a8f75b1a7a08bb8ab6ec28c1a33a8fb031 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 15:52:33 -0400
Subject: [PATCH 06/34] Other methods don't check for existence, add safety net
 elsewhere

---
 threadpoolctl.py | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index a8b12ab4..b9cd1a0a 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1174,8 +1174,7 @@ def _find_libraries_with_linux(self):
         filepaths = set(self._PATH_RE.findall(maps))
         for filepath in filepaths:
             filepath = filepath.decode("utf-8")
-            if os.path.exists(filepath):
-                self._make_controller_from_path(filepath)
+            self._make_controller_from_path(filepath)
 
     def _find_libraries_with_python(self, dllist):
         """Loop through loaded libraries and return binders on supported ones
@@ -1597,9 +1596,13 @@ def _make_controller_from_path(self, filepath):
             # expected library (e.g. a library having a common prefix with one of the
             # our supported libraries). Otherwise, create and store the library
             # controller.
-            lib_controller = controller_class(
-                filepath=filepath, prefix=prefix, parent=self
-            )
+            try:
+                lib_controller = controller_class(
+                    filepath=filepath, prefix=prefix, parent=self
+                )
+            except OSError:
+                # Probably because we couldn't load the filepath as a CDLL.
+                continue
 
             if filepath in (lib.filepath for lib in self.lib_controllers):
                 # We already have a controller for this library.

From e31a6a8a6b048193f18eac87a485e36f374f605d Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 16:22:44 -0400
Subject: [PATCH 07/34] Avoid /proc if there are safe alternatives.

---
 tests/test_threadpoolctl.py |  2 +-
 threadpoolctl.py            | 33 +++++++++++++++++++++++++--------
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index 35350110..57331282 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1146,7 +1146,7 @@ def create_controllers():
             backtrace_nogil(buf, 20)
 
     threads = []
-    for _ in range(os.cpu_count() * 4):
+    for _ in range(os.cpu_count()):
         t = Thread(target=create_controllers)
         threads.append(t)
         t.start()
diff --git a/threadpoolctl.py b/threadpoolctl.py
index b9cd1a0a..3cdbd149 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -56,7 +56,28 @@
 _SYSTEM_UINT = ctypes.c_uint64 if sys.maxsize > 2**32 else ctypes.c_uint32
 _SYSTEM_UINT_HALF = ctypes.c_uint32 if sys.maxsize > 2**32 else ctypes.c_uint16
 
-_PROCFS_EXISTS = sys.platform == "linux" and os.path.exists("/proc/self")
+# On glibc, dl_iterate_phdr has an internal lock, and that plus calling back
+# into Python and the need to (re)acquire the GIL can result in deadlocks. To
+# avoid that, listing shared libraries can use a Linux-specific mechanism that
+# doesn't have these issues (/proc/self/maaps). Since it's the Linux kernel,
+# musl works fine too.
+#
+# The downside is this mechanism is slower, so avoid it when safe alternatives
+# are available (Python 3.14+ with free-threading has dllist(), and no GIL to
+# cause deadlocks).
+_USE_PROCFS = (
+    # Only available on Linux:
+    sys.platform == "linux"
+    # Make sure /proc is mounted:
+    and os.path.exists("/proc/self")
+    # If dllist() is available, and there is no GIL, no need to use /proc. It's
+    # possible dllist() might work even if there is a GIL, but that's harder to
+    # prove. See https://github.com/python/cpython/issues/157573
+    and not (
+        sys.version_info[:2] >= (3, 14)
+        and not getattr(sys, "_is_gil_enabled", lambda: True)()
+    )
+)
 
 
 class _dl_phdr_info(ctypes.Structure):
@@ -1132,19 +1153,15 @@ def _load_libraries(self):
         # libffi builds (#225). dllist also uses dl_iterate_phdr internally
         # (#239), which we already avoid on Linux via /proc/self/maps.
         dllist = None
-        if sys.platform not in ("linux", "emscripten"):
+        if sys.platform != "emscripten":
             try:
                 from ctypes.util import dllist
             except ImportError:
                 # CPython before 3.14 does not provide dll inspection.
                 dllist = None
 
-        if _PROCFS_EXISTS:
-            # On glibc, dl_iterate_phdr has an internal lock, and that plus
-            # calling back into Python and the need to (re)acquire the GIL
-            # results in deadlocks. To avoid that, use a Linux-specific
-            # mechanism that doesn't have these issues; since it's Linux, musl
-            # works fine too.
+        if _USE_PROCFS:
+            # See comment on _USE_PROCFS.
             self._find_libraries_with_linux()
         elif dllist is not None:
             # On Python 3.14+, this functionality is built-in. Once Python 3.13

From 713ed718c1a6dee7eed49bd407c91da7e844ff95 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Tue, 15 Sep 2026 16:51:07 -0400
Subject: [PATCH 08/34] Note glibc 2.40

---
 tests/test_threadpoolctl.py |  3 +++
 threadpoolctl.py            | 15 ++++++++++-----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index 57331282..8b9db0e2 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1142,6 +1142,9 @@ def create_controllers():
         buf = (ctypes.c_void_p * 20)()
         for _ in range(100):
             limiter = threadpool_limits()
+            # On glibc 2.39, backtrace() calling dl_iterate_phdr() is enough to
+            # cause deadlocks. On 2.40 and later, they switched to a read-write
+            # lock, so this won't deadlock at all...
             backtrace_gil(buf, 20)
             backtrace_nogil(buf, 20)
 
diff --git a/threadpoolctl.py b/threadpoolctl.py
index 3cdbd149..3246ea07 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -56,15 +56,20 @@
 _SYSTEM_UINT = ctypes.c_uint64 if sys.maxsize > 2**32 else ctypes.c_uint32
 _SYSTEM_UINT_HALF = ctypes.c_uint32 if sys.maxsize > 2**32 else ctypes.c_uint16
 
-# On glibc, dl_iterate_phdr has an internal lock, and that plus calling back
-# into Python and the need to (re)acquire the GIL can result in deadlocks. To
-# avoid that, listing shared libraries can use a Linux-specific mechanism that
-# doesn't have these issues (/proc/self/maaps). Since it's the Linux kernel,
-# musl works fine too.
+# On glibc 2.39 and earlier, dl_iterate_phdr has an internal lock, and that
+# plus calling back into Python and the need to (re)acquire the GIL can result
+# in deadlocks. To avoid that, listing shared libraries can use a
+# Linux-specific mechanism that doesn't have these issues (/proc/self/maaps).
+# Since it's the Linux kernel, musl works fine too.
 #
 # The downside is this mechanism is slower, so avoid it when safe alternatives
 # are available (Python 3.14+ with free-threading has dllist(), and no GIL to
 # cause deadlocks).
+#
+# On glibc 2.40 and later, dl has a read-write lock, and dl_iterate_phdr should
+# only use the read version since it's not modifying anything. So you no longer
+# get deadlocks purely from dl_iterate_phdr. You can still deadlock with
+# dlopen() though.
 _USE_PROCFS = (
     # Only available on Linux:
     sys.platform == "linux"

From 6c798d46e39023ff98497066d14b58557b542c38 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:00:40 -0400
Subject: [PATCH 09/34] Make sure extensions don't prevent free threading

---
 tests/_openmp_test_helper/nested_prange_blas.pyx        | 2 ++
 tests/_openmp_test_helper/nested_prange_blas_custom.pyx | 2 ++
 tests/_openmp_test_helper/openmp_helpers_inner.pyx      | 2 ++
 tests/_openmp_test_helper/openmp_helpers_outer.pyx      | 2 ++
 4 files changed, 8 insertions(+)

diff --git a/tests/_openmp_test_helper/nested_prange_blas.pyx b/tests/_openmp_test_helper/nested_prange_blas.pyx
index af2a6693..ad3ef185 100644
--- a/tests/_openmp_test_helper/nested_prange_blas.pyx
+++ b/tests/_openmp_test_helper/nested_prange_blas.pyx
@@ -1,3 +1,5 @@
+# cython: freethreading_compatible = True
+
 cimport openmp
 from cython.parallel import parallel, prange
 
diff --git a/tests/_openmp_test_helper/nested_prange_blas_custom.pyx b/tests/_openmp_test_helper/nested_prange_blas_custom.pyx
index 6c0a9771..d76291e7 100644
--- a/tests/_openmp_test_helper/nested_prange_blas_custom.pyx
+++ b/tests/_openmp_test_helper/nested_prange_blas_custom.pyx
@@ -1,3 +1,5 @@
+# cython: freethreading_compatible = True
+
 cimport openmp
 from cython.parallel import parallel, prange
 
diff --git a/tests/_openmp_test_helper/openmp_helpers_inner.pyx b/tests/_openmp_test_helper/openmp_helpers_inner.pyx
index e7928d2f..566e7f4c 100644
--- a/tests/_openmp_test_helper/openmp_helpers_inner.pyx
+++ b/tests/_openmp_test_helper/openmp_helpers_inner.pyx
@@ -1,3 +1,5 @@
+# cython: freethreading_compatible = True
+
 cimport openmp
 from cython.parallel import prange
 
diff --git a/tests/_openmp_test_helper/openmp_helpers_outer.pyx b/tests/_openmp_test_helper/openmp_helpers_outer.pyx
index 2c8a383c..9e668f5c 100644
--- a/tests/_openmp_test_helper/openmp_helpers_outer.pyx
+++ b/tests/_openmp_test_helper/openmp_helpers_outer.pyx
@@ -1,3 +1,5 @@
+# cython: freethreading_compatible = True
+
 cimport openmp
 from cython.parallel import prange
 from openmp_helpers_inner cimport inner_openmp_loop

From 944d1f515821c21ea2e8afd9548d4b01844c0c24 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:18:19 -0400
Subject: [PATCH 10/34] More reliable deadlocks, including newer glibc

---
 tests/test_threadpoolctl.py | 28 ++++++++++++++++------------
 1 file changed, 16 insertions(+), 12 deletions(-)

diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index 8b9db0e2..24857895 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import ctypes
+import gc
 import json
 import os
 import pytest
@@ -1131,25 +1132,23 @@ def test_controller_parallelism_no_deadlocks():
     if sys.platform != "linux" or not hasattr(ctypes.PyDLL(None), "backtrace"):
         pytest.skip("Testing glibc on Linux")
 
-    # Internally, backtrace() calls dl_iterate_phdr which can result in
-    # deadlocks if threadpoolctl is also using dl_iterate_phdr.
-    backtrace_gil = ctypes.PyDLL(None).backtrace
-    backtrace_gil.argtypes = [ctypes.c_void_p, ctypes.c_int]
-    backtrace_nogil = ctypes.CDLL(None).backtrace
-    backtrace_nogil.argtypes = [ctypes.c_void_p, ctypes.c_int]
+    done = []
 
     def create_controllers():
         buf = (ctypes.c_void_p * 20)()
         for _ in range(100):
+            # May use dl_iterate_phdr() on Linux:
             limiter = threadpool_limits()
-            # On glibc 2.39, backtrace() calling dl_iterate_phdr() is enough to
-            # cause deadlocks. On 2.40 and later, they switched to a read-write
-            # lock, so this won't deadlock at all...
-            backtrace_gil(buf, 20)
-            backtrace_nogil(buf, 20)
+            # dlopen():
+            try:
+                dll = ctypes.CDLL("libncurses.so.6")
+                del dll
+            except OSError:
+                done.append(False)
+        done.append(True)
 
     threads = []
-    for _ in range(os.cpu_count()):
+    for _ in range(os.cpu_count() * 4):
         t = Thread(target=create_controllers)
         threads.append(t)
         t.start()
@@ -1157,6 +1156,11 @@ def create_controllers():
     for t in threads:
         t.join()
 
+    if False in done:
+        pytest.skip("libncurses.so.6 not available")
+
+    assert len(done) == os.cpu_count() * 4
+
 
 @pytest.mark.skipif(
     not sys.platform.startswith("linux"),

From 2cc8f692d4c320dbae7e18de349300f7eb828e8d Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:31:24 -0400
Subject: [PATCH 11/34] Update with latest understanding

---
 threadpoolctl.py | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 3246ea07..7df4fb5b 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -58,26 +58,30 @@
 
 # On glibc 2.39 and earlier, dl_iterate_phdr has an internal lock, and that
 # plus calling back into Python and the need to (re)acquire the GIL can result
-# in deadlocks. To avoid that, listing shared libraries can use a
-# Linux-specific mechanism that doesn't have these issues (/proc/self/maaps).
-# Since it's the Linux kernel, musl works fine too.
-#
-# The downside is this mechanism is slower, so avoid it when safe alternatives
-# are available (Python 3.14+ with free-threading has dllist(), and no GIL to
-# cause deadlocks).
+# in deadlocks.
 #
 # On glibc 2.40 and later, dl has a read-write lock, and dl_iterate_phdr should
 # only use the read version since it's not modifying anything. So you no longer
 # get deadlocks purely from dl_iterate_phdr. You can still deadlock with
 # dlopen() though.
+#
+# To avoid that deadlock, listing shared libraries can use a Linux-specific
+# mechanism that doesn't have these issues (/proc/self/maps). Since it's the
+# Linux kernel, musl works fine too.
+#
+# The downside is this mechanism is slower, so avoid it when safe alternatives
+# are available.
 _USE_PROCFS = (
     # Only available on Linux:
     sys.platform == "linux"
     # Make sure /proc is mounted:
     and os.path.exists("/proc/self")
-    # If dllist() is available, and there is no GIL, no need to use /proc. It's
-    # possible dllist() might work even if there is a GIL, but that's harder to
-    # prove. See https://github.com/python/cpython/issues/157573
+    # If dllist() is available (3.14+), and there is no GIL, no need to use
+    # /proc. It's possible dllist() might work in GIL builds too starting in
+    # Python 3.15, where it is written in C instead of being equivalent to
+    # threadpoolctl's implementation. But see
+    # https://github.com/python/cpython/issues/157573. We should consider
+    # enabling it on GIL Python too once threadpoolctl supports 3.15.
     and not (
         sys.version_info[:2] >= (3, 14)
         and not getattr(sys, "_is_gil_enabled", lambda: True)()

From 8dd87e37ddf95d2c47a8a26370cf668e6b7a9d5f Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:45:15 -0400
Subject: [PATCH 12/34] Cleanups

---
 tests/test_threadpoolctl.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index 24857895..0aebee0c 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 import ctypes
-import gc
 import json
 import os
 import pytest
@@ -1141,10 +1140,14 @@ def create_controllers():
             limiter = threadpool_limits()
             # dlopen():
             try:
+                # Should be available in most Linux, and importantly isn't
+                # loaded by default into Python:
                 dll = ctypes.CDLL("libncurses.so.6")
                 del dll
             except OSError:
                 done.append(False)
+                return
+            del limiter
         done.append(True)
 
     threads = []

From b43e0562d27c147bd5d9b994abfebd7198980881 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:45:20 -0400
Subject: [PATCH 13/34] dllist() is ok on Python 3.15

---
 threadpoolctl.py | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 7df4fb5b..f47bc2cd 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -76,14 +76,13 @@
     sys.platform == "linux"
     # Make sure /proc is mounted:
     and os.path.exists("/proc/self")
-    # If dllist() is available (3.14+), and there is no GIL, no need to use
-    # /proc. It's possible dllist() might work in GIL builds too starting in
-    # Python 3.15, where it is written in C instead of being equivalent to
-    # threadpoolctl's implementation. But see
-    # https://github.com/python/cpython/issues/157573. We should consider
+    # If dllist() is available (3.14+), written in C so no risk of GC part way
+    # (3.15+), and there is no GIL, no need to use /proc, since dllist() is
+    # faster. It's possible dllist() might work in GIL builds too but see
+    # https://github.com/python/cpython/issues/157573. So we should consider
     # enabling it on GIL Python too once threadpoolctl supports 3.15.
     and not (
-        sys.version_info[:2] >= (3, 14)
+        sys.version_info[:2] >= (3, 15)
         and not getattr(sys, "_is_gil_enabled", lambda: True)()
     )
 )
@@ -1162,7 +1161,10 @@ def _load_libraries(self):
         # libffi builds (#225). dllist also uses dl_iterate_phdr internally
         # (#239), which we already avoid on Linux via /proc/self/maps.
         dllist = None
-        if sys.platform != "emscripten":
+        if sys.platform != "emscripten" or (
+            # Python 3.15 doesn't have the CFUNCTYPE anymore:
+            sys.platform == "linux" and sys.version_info[:2] >= (3, 15)
+        ):
             try:
                 from ctypes.util import dllist
             except ImportError:

From e87c8fedd1fad0fd3a466a06f179c25eb9ff7fd8 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:56:05 -0400
Subject: [PATCH 14/34] Changelog entry

---
 CHANGES.md | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/CHANGES.md b/CHANGES.md
index a23ce6e0..2529e3bc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,7 +1,10 @@
 3.8.0 (under development)
 =========================
 
-TODO: update me.
+- Run faster on Linux, where the new `/proc/self/maps` mechanism in 3.7.0 added
+  quite a bit of overhead.
+  https://github.com/joblib/threadpoolctl/pull/250
+
 
 3.7.0 (2026-09-15)
 ==================

From f7d625e9b210bdef88d214dd122076982d33f771 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 11:57:32 -0400
Subject: [PATCH 15/34] Reformat with black to match CI

---
 threadpoolctl.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index f47bc2cd..bb963c26 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1163,7 +1163,8 @@ def _load_libraries(self):
         dllist = None
         if sys.platform != "emscripten" or (
             # Python 3.15 doesn't have the CFUNCTYPE anymore:
-            sys.platform == "linux" and sys.version_info[:2] >= (3, 15)
+            sys.platform == "linux"
+            and sys.version_info[:2] >= (3, 15)
         ):
             try:
                 from ctypes.util import dllist

From c75c9f774c50e90841acba2d67899929dd274abe Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Wed, 16 Sep 2026 12:02:06 -0400
Subject: [PATCH 16/34] Correct ctypes.util logic on Linux

---
 tests/test_threadpoolctl.py | 6 +++++-
 threadpoolctl.py            | 2 +-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index 0aebee0c..f13f9c99 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1167,7 +1167,11 @@ def create_controllers():
 
 @pytest.mark.skipif(
     not sys.platform.startswith("linux"),
-    reason="ctypes.util is only avoided on Linux (#225)",
+    reason="ctypes.util is only avoided on Linux (#225) in Python 3.14",
+)
+@pytest.mark.skipif(
+    sys.version_info[:2] >= (3, 15),
+    reason="Python 3.15 shouldn't have the issue in #225",
 )
 def test_linux_does_not_import_ctypes_util():
     # ctypes.util on CPython 3.14 Linux allocates a process-lifetime CFUNCTYPE
diff --git a/threadpoolctl.py b/threadpoolctl.py
index bb963c26..41bb5994 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -1161,7 +1161,7 @@ def _load_libraries(self):
         # libffi builds (#225). dllist also uses dl_iterate_phdr internally
         # (#239), which we already avoid on Linux via /proc/self/maps.
         dllist = None
-        if sys.platform != "emscripten" or (
+        if sys.platform != "emscripten" and (
             # Python 3.15 doesn't have the CFUNCTYPE anymore:
             sys.platform == "linux"
             and sys.version_info[:2] >= (3, 15)

From c0abb0a7fdc027a2018ccae0f5dd2e0bde85f744 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 11:48:31 -0400
Subject: [PATCH 17/34] Apply batched suggestions from code review, removing
 dead code

Co-authored-by: Olivier Grisel <olivier.grisel@ensta.org>
---
 tests/test_threadpoolctl.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index f13f9c99..654c3fdd 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1128,13 +1128,12 @@ def test_controller_parallelism_no_deadlocks():
     Lacking the fixes from PR #243, this deadlocks on Conda environments, at
     least, but possibly not on PyPI with Python from a Linux distro.
     """
-    if sys.platform != "linux" or not hasattr(ctypes.PyDLL(None), "backtrace"):
+    if sys.platform != "linux":
         pytest.skip("Testing glibc on Linux")
 
     done = []
 
     def create_controllers():
-        buf = (ctypes.c_void_p * 20)()
         for _ in range(100):
             # May use dl_iterate_phdr() on Linux:
             limiter = threadpool_limits()

From 3d2e5f56e61388e8a02bb29c82aae0c9ae34ac27 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 11:57:21 -0400
Subject: [PATCH 18/34] Additional runners

---
 .github/workflows/test.yml | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 64304eae..b58bba6e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -221,6 +221,39 @@ jobs:
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
 
+          # Python 3.15, with GIL
+          - name: py315_gil_pip_openblas
+            os: ubuntu-latest
+            PACKAGER: "pip"
+            PYTHON_VERSION: "3.15-dev"
+            CC_OUTER_LOOP: "gcc"
+            CC_INNER_LOOP: "gcc"
+
+          # Python 3.15, free-threaded
+          - name: py315_freethreaded_pip_openblas
+            os: ubuntu-latest
+            PACKAGER: "pip"
+            PYTHON_VERSION: "3.15t-dev"
+            CC_OUTER_LOOP: "gcc"
+            CC_INNER_LOOP: "gcc"
+
+          # Python 3.14, free-threaded
+          - name: py315_freethreaded_pip_openblas
+            os: ubuntu-latest
+            PACKAGER: "pip"
+            PYTHON_VERSION: "3.14t"
+            CC_OUTER_LOOP: "gcc"
+            CC_INNER_LOOP: "gcc"
+
+          # Ubuntu 24.04, which has glibc with different dl_iterate_phdr than
+          # latest Ubuntus.
+          - name: ubuntu24_04
+            os: ubuntu-24.04
+            PACKAGER: "pip"
+            PYTHON_VERSION: "3.14"
+            CC_OUTER_LOOP: "gcc"
+            CC_INNER_LOOP: "gcc"
+
     env: ${{ matrix }}
 
     runs-on: ${{ matrix.os }}

From 8755aeebc3c2e0042ad25e2c52d1db6abf7a2617 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:27:32 -0400
Subject: [PATCH 19/34] Much more aggressive (and therefore robust) test for
 deadlocks.

---
 conftest.py                        |  1 +
 tests/_dl_iterate_phdr_deadlock.py | 69 ++++++++++++++++++++++++++++++
 tests/test_threadpoolctl.py        | 50 +++++++---------------
 3 files changed, 85 insertions(+), 35 deletions(-)
 create mode 100644 tests/_dl_iterate_phdr_deadlock.py

diff --git a/conftest.py b/conftest.py
index 53baddff..ad3e8ad3 100644
--- a/conftest.py
+++ b/conftest.py
@@ -2,4 +2,5 @@
     "tests/empirical_scope_observation.py",
     "tests/_openmp_test_helper.py",
     "tests/_limit_blas.py",
+    "tests/_dl_iterate_phdr_deadlock.py"
 ]
diff --git a/tests/_dl_iterate_phdr_deadlock.py b/tests/_dl_iterate_phdr_deadlock.py
new file mode 100644
index 00000000..ac98c36a
--- /dev/null
+++ b/tests/_dl_iterate_phdr_deadlock.py
@@ -0,0 +1,69 @@
+"""Try to trigger deadlock via dl_iterate_phdr."""
+
+import ctypes
+import os
+import sys
+from threading import Thread
+
+from threadpoolctl import threadpool_limits
+
+
+def create_controllers(done):
+    for _ in range(100):
+        # May use dl_iterate_phdr() on Linux:
+        limiter = threadpool_limits()
+        # dlopen() of some shared libraries like to be installed:
+        loaded = False
+        # Common libraries on Ubuntu:
+        for name in [
+            "libncurses.so.6",
+            "libncursesw.so.6",
+            "libgmp.so.10",
+            "libssl.so.3",
+            "libcrypt.so.1",
+        ]:
+            try:
+                dll = ctypes.CDLL(name)
+                del dll
+                loaded = True
+            except OSError:
+                pass
+        if not loaded:
+            # Couldn't do an dlopen()s.
+            os._exit(7)
+
+        # Imports, which also do dlopen():
+        import numpy  # also gets us BLAS
+        import _pickle
+
+        try:
+            import tests._openmp_test_helper.nested_prange_blas
+        except ImportError:
+            pass
+
+        del limiter
+
+    done.append(True)
+
+
+def main():
+    threads = []
+    done = []
+
+    for _ in range(os.cpu_count() * 4):
+        t = Thread(target=create_controllers, args=(done,))
+        threads.append(t)
+        t.start()
+
+    for t in threads:
+        t.join()
+
+    if len(done) != os.cpu_count() * 4:
+        sys.exit(1)
+
+    # Special success exist code:
+    sys.exit(17)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/tests/test_threadpoolctl.py b/tests/test_threadpoolctl.py
index 654c3fdd..75a6ac9a 100644
--- a/tests/test_threadpoolctl.py
+++ b/tests/test_threadpoolctl.py
@@ -1121,47 +1121,27 @@ def test_conda_blas_detection_after_import(module):
 
 
 def test_controller_parallelism_no_deadlocks():
-    """Creating a controller in parallel to itself does not cause deadlocks.
+    """
+    Creating a controller in parallel to itself and other operations loading
+    shared libraries does not cause deadlocks.
 
     Non-regression test for https://github.com/joblib/threadpoolctl/issues/239
-
-    Lacking the fixes from PR #243, this deadlocks on Conda environments, at
-    least, but possibly not on PyPI with Python from a Linux distro.
     """
     if sys.platform != "linux":
         pytest.skip("Testing glibc on Linux")
 
-    done = []
-
-    def create_controllers():
-        for _ in range(100):
-            # May use dl_iterate_phdr() on Linux:
-            limiter = threadpool_limits()
-            # dlopen():
-            try:
-                # Should be available in most Linux, and importantly isn't
-                # loaded by default into Python:
-                dll = ctypes.CDLL("libncurses.so.6")
-                del dll
-            except OSError:
-                done.append(False)
-                return
-            del limiter
-        done.append(True)
-
-    threads = []
-    for _ in range(os.cpu_count() * 4):
-        t = Thread(target=create_controllers)
-        threads.append(t)
-        t.start()
-
-    for t in threads:
-        t.join()
-
-    if False in done:
-        pytest.skip("libncurses.so.6 not available")
-
-    assert len(done) == os.cpu_count() * 4
+    # Deadlock isn't always reliable, so run multiple times:
+    for _ in range(10):
+        process = subprocess.run(
+            [sys.executable, "-m", "tests._dl_iterate_phdr_deadlock"], timeout=10
+        )
+
+        if process.returncode == 7:
+            # Special code indicating it couldn't load any shared libraries.
+            pytest.skip("Couldn't find any of the exected shared libraries")
+
+        # Special code indicating success:
+        assert process.returncode == 17
 
 
 @pytest.mark.skipif(

From e6b88711b43d1f7c80681d387f8a3266c565e06d Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:32:39 -0400
Subject: [PATCH 20/34] Maybe correct freethreading installations

---
 .github/workflows/test.yml        | 16 +++++++++-------
 continuous_integration/install.sh |  4 +++-
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index b58bba6e..f0ed7ac8 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -224,24 +224,26 @@ jobs:
           # Python 3.15, with GIL
           - name: py315_gil_pip_openblas
             os: ubuntu-latest
-            PACKAGER: "pip"
-            PYTHON_VERSION: "3.15-dev"
+            PACKAGER: "conda-forge"
+            PYTHON_VERSION: "3.15"
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
 
           # Python 3.15, free-threaded
           - name: py315_freethreaded_pip_openblas
             os: ubuntu-latest
-            PACKAGER: "pip"
-            PYTHON_VERSION: "3.15t-dev"
+            PACKAGER: "conda-forge"
+            PYTHON_VERSION: "3.15"
+            FREETHREADING: "1"
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
 
           # Python 3.14, free-threaded
           - name: py315_freethreaded_pip_openblas
             os: ubuntu-latest
-            PACKAGER: "pip"
-            PYTHON_VERSION: "3.14t"
+            PACKAGER: "conda-forge"
+            PYTHON_VERSION: "3.14"
+            FREETHREADING: "1"
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
 
@@ -249,7 +251,7 @@ jobs:
           # latest Ubuntus.
           - name: ubuntu24_04
             os: ubuntu-24.04
-            PACKAGER: "pip"
+            PACKAGER: "conda-forge"
             PYTHON_VERSION: "3.14"
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index cd9fc2d2..b6841e3d 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -41,7 +41,9 @@ make_conda() {
         fi
     fi
 
-    if [[ "$PYTHON_VERSION" == "*" ]]; then
+    if [[ "$FREETHREADING" == "1"]]; then
+        TO_INSTALL="$TO_INSTALL python-freethreading"
+    elif [[ "$PYTHON_VERSION" == "*" ]]; then
         # Avoid installing free-threaded python
         TO_INSTALL="$TO_INSTALL python-gil"
     fi

From 0dc7249bc26702111d4e554c319e3df5c6410d85 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:34:10 -0400
Subject: [PATCH 21/34] Reformat

---
 conftest.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/conftest.py b/conftest.py
index ad3e8ad3..11855652 100644
--- a/conftest.py
+++ b/conftest.py
@@ -2,5 +2,5 @@
     "tests/empirical_scope_observation.py",
     "tests/_openmp_test_helper.py",
     "tests/_limit_blas.py",
-    "tests/_dl_iterate_phdr_deadlock.py"
+    "tests/_dl_iterate_phdr_deadlock.py",
 ]

From a31a0ab73359006ab2492c4f44e5ff31556f7dad Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:38:52 -0400
Subject: [PATCH 22/34] Check for GIL on every call since imports can change.

Also move some checks out to save a little time.
---
 threadpoolctl.py | 84 ++++++++++++++++++++++++------------------------
 1 file changed, 42 insertions(+), 42 deletions(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 41bb5994..9690121e 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -24,6 +24,22 @@
 from functools import lru_cache
 from contextlib import ContextDecorator
 
+# ctypes.util is not imported on Linux: on CPython 3.14 it allocates a
+# process-lifetime CFUNCTYPE callback that is not fork-safe with some libffi
+# builds (#225). dllist also uses dl_iterate_phdr internally (#239), which we
+# already avoid on Linux via /proc/self/maps on older versions of Python.
+dllist = None
+if sys.platform != "emscripten" and (
+    # Python 3.15 doesn't have the CFUNCTYPE anymore:
+    sys.platform == "linux" and sys.version_info[:2] >= (3, 15)
+):
+    try:
+        from ctypes.util import dllist
+    except ImportError:
+        # CPython before 3.14 does not provide dll inspection.
+        dllist = None
+
+
 __version__ = "3.8.0.dev0"
 __all__ = [
     "threadpool_limits",
@@ -56,35 +72,12 @@
 _SYSTEM_UINT = ctypes.c_uint64 if sys.maxsize > 2**32 else ctypes.c_uint32
 _SYSTEM_UINT_HALF = ctypes.c_uint32 if sys.maxsize > 2**32 else ctypes.c_uint16
 
-# On glibc 2.39 and earlier, dl_iterate_phdr has an internal lock, and that
-# plus calling back into Python and the need to (re)acquire the GIL can result
-# in deadlocks.
-#
-# On glibc 2.40 and later, dl has a read-write lock, and dl_iterate_phdr should
-# only use the read version since it's not modifying anything. So you no longer
-# get deadlocks purely from dl_iterate_phdr. You can still deadlock with
-# dlopen() though.
-#
-# To avoid that deadlock, listing shared libraries can use a Linux-specific
-# mechanism that doesn't have these issues (/proc/self/maps). Since it's the
-# Linux kernel, musl works fine too.
-#
-# The downside is this mechanism is slower, so avoid it when safe alternatives
-# are available.
-_USE_PROCFS = (
+
+_HAS_PROCFS = (
     # Only available on Linux:
     sys.platform == "linux"
     # Make sure /proc is mounted:
     and os.path.exists("/proc/self")
-    # If dllist() is available (3.14+), written in C so no risk of GC part way
-    # (3.15+), and there is no GIL, no need to use /proc, since dllist() is
-    # faster. It's possible dllist() might work in GIL builds too but see
-    # https://github.com/python/cpython/issues/157573. So we should consider
-    # enabling it on GIL Python too once threadpoolctl supports 3.15.
-    and not (
-        sys.version_info[:2] >= (3, 15)
-        and not getattr(sys, "_is_gil_enabled", lambda: True)()
-    )
 )
 
 
@@ -1156,24 +1149,31 @@ def __len__(self):
 
     def _load_libraries(self):
         """Loop through loaded shared libraries and store the supported ones"""
-        # ctypes.util is not imported on Linux: on CPython 3.14 it allocates a
-        # process-lifetime CFUNCTYPE callback that is not fork-safe with some
-        # libffi builds (#225). dllist also uses dl_iterate_phdr internally
-        # (#239), which we already avoid on Linux via /proc/self/maps.
-        dllist = None
-        if sys.platform != "emscripten" and (
-            # Python 3.15 doesn't have the CFUNCTYPE anymore:
-            sys.platform == "linux"
-            and sys.version_info[:2] >= (3, 15)
+        # On glibc 2.39 and earlier, dl_iterate_phdr has an internal lock, and
+        # that plus calling back into Python and the need to (re)acquire the
+        # GIL can result in deadlocks.
+        #
+        # On glibc 2.40 and later, dl has a read-write lock, and
+        # dl_iterate_phdr should only use the read version since it's not
+        # modifying anything. So you no longer get deadlocks purely from
+        # dl_iterate_phdr. You can still deadlock with dlopen() though.
+        #
+        # To avoid that deadlock, listing shared libraries can use a
+        # Linux-specific mechanism that doesn't have these issues
+        # (/proc/self/maps). Since it's the Linux kernel, musl works fine too.
+        #
+        # The downside is this mechanism is slower, so avoid it when safe
+        # alternatives are available. In particular, if dllist() is available
+        # (3.14+), written in C so no risk of GC part way (3.15+), and there is
+        # no GIL, no need to use /proc, since dllist() is faster. It's possible
+        # dllist() might work in GIL builds too but see
+        # https://github.com/python/cpython/issues/157573. So we should
+        # consider enabling it on GIL Python too once threadpoolctl supports
+        # 3.15.
+        if _HAS_PROCFS and not (
+            sys.version_info[:2] >= (3, 15)
+            and not getattr(sys, "_is_gil_enabled", lambda: True)()
         ):
-            try:
-                from ctypes.util import dllist
-            except ImportError:
-                # CPython before 3.14 does not provide dll inspection.
-                dllist = None
-
-        if _USE_PROCFS:
-            # See comment on _USE_PROCFS.
             self._find_libraries_with_linux()
         elif dllist is not None:
             # On Python 3.14+, this functionality is built-in. Once Python 3.13

From 59c8a637cf266cda849ccc5c54203c1a31f361d4 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:42:47 -0400
Subject: [PATCH 23/34] Reformat harder

---
 threadpoolctl.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/threadpoolctl.py b/threadpoolctl.py
index 9690121e..177bb244 100644
--- a/threadpoolctl.py
+++ b/threadpoolctl.py
@@ -31,7 +31,8 @@
 dllist = None
 if sys.platform != "emscripten" and (
     # Python 3.15 doesn't have the CFUNCTYPE anymore:
-    sys.platform == "linux" and sys.version_info[:2] >= (3, 15)
+    sys.platform == "linux"
+    and sys.version_info[:2] >= (3, 15)
 ):
     try:
         from ctypes.util import dllist

From 82d130cce0e4b2953e8f7bf95e4a229f4779f41a Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:44:39 -0400
Subject: [PATCH 24/34] I love bash

---
 continuous_integration/install.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index b6841e3d..42c551ba 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -41,7 +41,7 @@ make_conda() {
         fi
     fi
 
-    if [[ "$FREETHREADING" == "1"]]; then
+    if [[ "$FREETHREADING" == "1" ]]; then
         TO_INSTALL="$TO_INSTALL python-freethreading"
     elif [[ "$PYTHON_VERSION" == "*" ]]; then
         # Avoid installing free-threaded python

From 152f1db0bf522c068ee1e855d05b64f149ad65a7 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:47:24 -0400
Subject: [PATCH 25/34] Tell it which blas

---
 .github/workflows/test.yml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f0ed7ac8..94e77743 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -225,6 +225,7 @@ jobs:
           - name: py315_gil_pip_openblas
             os: ubuntu-latest
             PACKAGER: "conda-forge"
+            BLAS: "openblas"
             PYTHON_VERSION: "3.15"
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
@@ -233,6 +234,7 @@ jobs:
           - name: py315_freethreaded_pip_openblas
             os: ubuntu-latest
             PACKAGER: "conda-forge"
+            BLAS: "openblas"
             PYTHON_VERSION: "3.15"
             FREETHREADING: "1"
             CC_OUTER_LOOP: "gcc"
@@ -242,6 +244,7 @@ jobs:
           - name: py315_freethreaded_pip_openblas
             os: ubuntu-latest
             PACKAGER: "conda-forge"
+            BLAS: "openblas"
             PYTHON_VERSION: "3.14"
             FREETHREADING: "1"
             CC_OUTER_LOOP: "gcc"
@@ -252,6 +255,7 @@ jobs:
           - name: ubuntu24_04
             os: ubuntu-24.04
             PACKAGER: "conda-forge"
+            BLAS: "openblas"
             PYTHON_VERSION: "3.14"
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"

From 0883c2afc20c767263af05adde88429ae9cc6100 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:50:03 -0400
Subject: [PATCH 26/34] Not always available

---
 tests/_dl_iterate_phdr_deadlock.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tests/_dl_iterate_phdr_deadlock.py b/tests/_dl_iterate_phdr_deadlock.py
index ac98c36a..f55af53e 100644
--- a/tests/_dl_iterate_phdr_deadlock.py
+++ b/tests/_dl_iterate_phdr_deadlock.py
@@ -33,7 +33,10 @@ def create_controllers(done):
             os._exit(7)
 
         # Imports, which also do dlopen():
-        import numpy  # also gets us BLAS
+        try:
+            import numpy  # also gets us BLAS
+        except ImportError:
+            pass
         import _pickle
 
         try:

From cbd587df6affd47c3c94b92091cc61be59053dc1 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:52:17 -0400
Subject: [PATCH 27/34] Add a channel for rcs

---
 continuous_integration/install.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index 42c551ba..72a84248 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -83,7 +83,7 @@ elif [[ "$PACKAGER" == "conda-forge" ]]; then
     if [[ "$INSTALL_OPENCV" == "true" ]]; then
         TO_INSTALL="$TO_INSTALL opencv"
     fi
-    make_conda "conda-forge" "$TO_INSTALL"
+    make_conda "conda-forge" "$TO_INSTALL -c conda-forge/label/python_rc"
 
 elif [[ "$PACKAGER" == "pip" ]]; then
     # Use conda to build an empty python env and then use pip to install

From 5090cbb5f7cd462d56849513565d22c5975f3d08 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 12:56:07 -0400
Subject: [PATCH 28/34] A better way

---
 continuous_integration/install.sh | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index 72a84248..64060675 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -53,6 +53,10 @@ make_conda() {
     # prevent mixing conda channels
     conda config --set channel_priority strict
     conda config --add channels $CHANNEL
+    if [[ "$CHANNEL" == "conda-forge" ]]; then
+        # Support Python release candidates
+        conda config --add channels conda-forge/label/python_rc
+    fi
 
     conda update -n base conda conda-libmamba-solver -q --yes
     conda config --set solver libmamba
@@ -83,7 +87,7 @@ elif [[ "$PACKAGER" == "conda-forge" ]]; then
     if [[ "$INSTALL_OPENCV" == "true" ]]; then
         TO_INSTALL="$TO_INSTALL opencv"
     fi
-    make_conda "conda-forge" "$TO_INSTALL -c conda-forge/label/python_rc"
+    make_conda "conda-forge" "$TO_INSTALL"
 
 elif [[ "$PACKAGER" == "pip" ]]; then
     # Use conda to build an empty python env and then use pip to install

From 83ecfb363fb814dc2fc2c93ff7b5bf0c1e548f6b Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 13:02:12 -0400
Subject: [PATCH 29/34] Try a different approach

---
 continuous_integration/install.sh | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index 64060675..e91ed12e 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -50,10 +50,9 @@ make_conda() {
 
     # Need to source conda.sh before first conda command
     source "$CONDA/etc/profile.d/conda.sh"
-    # prevent mixing conda channels
-    conda config --set channel_priority strict
-    conda config --add channels $CHANNEL
     if [[ "$CHANNEL" == "conda-forge" ]]; then
+        conda config --add channels conda-forge
+        conda config --remove channels defaults
         # Support Python release candidates
         conda config --add channels conda-forge/label/python_rc
     fi

From b5d9071d4ee7722d1ad14465d7c53313905c4787 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 13:03:09 -0400
Subject: [PATCH 30/34] Better order

---
 continuous_integration/install.sh | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index e91ed12e..ed97bc11 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -50,6 +50,9 @@ make_conda() {
 
     # Need to source conda.sh before first conda command
     source "$CONDA/etc/profile.d/conda.sh"
+    conda update -n base conda conda-libmamba-solver -q --yes
+    conda config --set solver libmamba
+
     if [[ "$CHANNEL" == "conda-forge" ]]; then
         conda config --add channels conda-forge
         conda config --remove channels defaults
@@ -57,9 +60,6 @@ make_conda() {
         conda config --add channels conda-forge/label/python_rc
     fi
 
-    conda update -n base conda conda-libmamba-solver -q --yes
-    conda config --set solver libmamba
-
     conda create -n testenv -q --yes python=$PYTHON_VERSION $TO_INSTALL
     conda activate testenv
 }

From 4a0b442fbdbe38fcc40d06a7216b7762e2528668 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 13:06:59 -0400
Subject: [PATCH 31/34] Conda claims no defaults?

---
 continuous_integration/install.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index ed97bc11..3e492c43 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -53,9 +53,10 @@ make_conda() {
     conda update -n base conda conda-libmamba-solver -q --yes
     conda config --set solver libmamba
 
+    conda config --show-sources
+
     if [[ "$CHANNEL" == "conda-forge" ]]; then
         conda config --add channels conda-forge
-        conda config --remove channels defaults
         # Support Python release candidates
         conda config --add channels conda-forge/label/python_rc
     fi

From 2ca058e73add2e93d95baf692e860f2983136c97 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 13:10:23 -0400
Subject: [PATCH 32/34] Maybe this'll fix it

---
 continuous_integration/install.sh | 1 +
 1 file changed, 1 insertion(+)

diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index 3e492c43..a1e5b2f1 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -59,6 +59,7 @@ make_conda() {
         conda config --add channels conda-forge
         # Support Python release candidates
         conda config --add channels conda-forge/label/python_rc
+        conda config --add channels conda-forge/label/numpy_rc
     fi
 
     conda create -n testenv -q --yes python=$PYTHON_VERSION $TO_INSTALL

From d3d322ead46024d96f0fb72d9a9217af63810601 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 13:14:45 -0400
Subject: [PATCH 33/34] Drop Python 3.15 for now

---
 .github/workflows/test.yml        | 19 -------------------
 continuous_integration/install.sh | 13 ++++---------
 2 files changed, 4 insertions(+), 28 deletions(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 94e77743..046a2d0f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -221,25 +221,6 @@ jobs:
             CC_OUTER_LOOP: "gcc"
             CC_INNER_LOOP: "gcc"
 
-          # Python 3.15, with GIL
-          - name: py315_gil_pip_openblas
-            os: ubuntu-latest
-            PACKAGER: "conda-forge"
-            BLAS: "openblas"
-            PYTHON_VERSION: "3.15"
-            CC_OUTER_LOOP: "gcc"
-            CC_INNER_LOOP: "gcc"
-
-          # Python 3.15, free-threaded
-          - name: py315_freethreaded_pip_openblas
-            os: ubuntu-latest
-            PACKAGER: "conda-forge"
-            BLAS: "openblas"
-            PYTHON_VERSION: "3.15"
-            FREETHREADING: "1"
-            CC_OUTER_LOOP: "gcc"
-            CC_INNER_LOOP: "gcc"
-
           # Python 3.14, free-threaded
           - name: py315_freethreaded_pip_openblas
             os: ubuntu-latest
diff --git a/continuous_integration/install.sh b/continuous_integration/install.sh
index a1e5b2f1..42c551ba 100755
--- a/continuous_integration/install.sh
+++ b/continuous_integration/install.sh
@@ -50,18 +50,13 @@ make_conda() {
 
     # Need to source conda.sh before first conda command
     source "$CONDA/etc/profile.d/conda.sh"
+    # prevent mixing conda channels
+    conda config --set channel_priority strict
+    conda config --add channels $CHANNEL
+
     conda update -n base conda conda-libmamba-solver -q --yes
     conda config --set solver libmamba
 
-    conda config --show-sources
-
-    if [[ "$CHANNEL" == "conda-forge" ]]; then
-        conda config --add channels conda-forge
-        # Support Python release candidates
-        conda config --add channels conda-forge/label/python_rc
-        conda config --add channels conda-forge/label/numpy_rc
-    fi
-
     conda create -n testenv -q --yes python=$PYTHON_VERSION $TO_INSTALL
     conda activate testenv
 }

From 59f9b327c57c90358f41cb7813ea11b7206ebc77 Mon Sep 17 00:00:00 2001
From: Itamar Turner-Trauring <itamar@itamarst.org>
Date: Thu, 17 Sep 2026 13:18:12 -0400
Subject: [PATCH 34/34] Correct the name

---
 .github/workflows/test.yml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 046a2d0f..a77b1c5f 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -222,7 +222,7 @@ jobs:
             CC_INNER_LOOP: "gcc"
 
           # Python 3.14, free-threaded
-          - name: py315_freethreaded_pip_openblas
+          - name: py314_freethreaded_pip_openblas
             os: ubuntu-latest
             PACKAGER: "conda-forge"
             BLAS: "openblas"