From ab719e1bdb5d73cabe7c063f45f21fd295bd2f9d Mon Sep 17 00:00:00 2001
From: Nathan Goldbaum <nathan.goldbaum@gmail.com>
Date: Tue, 16 Apr 2024 12:44:49 -0600
Subject: [PATCH 1/3] MNT: disable the coercion cache for the nogil build

---
 numpy/_core/src/multiarray/array_coercion.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/numpy/_core/src/multiarray/array_coercion.c b/numpy/_core/src/multiarray/array_coercion.c
index f63dbbc77e1f..443239274ea3 100644
--- a/numpy/_core/src/multiarray/array_coercion.c
+++ b/numpy/_core/src/multiarray/array_coercion.c
@@ -614,10 +614,13 @@ update_shape(int curr_ndim, int *max_ndim,
     return success;
 }
 
-
+#ifndef Py_GIL_DISABLED
 #define COERCION_CACHE_CACHE_SIZE 5
 static int _coercion_cache_num = 0;
 static coercion_cache_obj *_coercion_cache_cache[COERCION_CACHE_CACHE_SIZE];
+#else
+#define COERCION_CACHE_CACHE_SIZE 0
+#endif
 
 /*
  * Steals a reference to the object.
@@ -628,11 +631,14 @@ npy_new_coercion_cache(
         coercion_cache_obj ***next_ptr, int ndim)
 {
     coercion_cache_obj *cache;
+#if COERCION_CACHE_CACHE_SIZE > 0
     if (_coercion_cache_num > 0) {
         _coercion_cache_num--;
         cache = _coercion_cache_cache[_coercion_cache_num];
     }
-    else {
+    else
+#endif
+    {
         cache = PyMem_Malloc(sizeof(coercion_cache_obj));
     }
     if (cache == NULL) {
@@ -661,11 +667,14 @@ npy_unlink_coercion_cache(coercion_cache_obj *current)
 {
     coercion_cache_obj *next = current->next;
     Py_DECREF(current->arr_or_sequence);
+#if COERCION_CACHE_CACHE_SIZE > 0
     if (_coercion_cache_num < COERCION_CACHE_CACHE_SIZE) {
         _coercion_cache_cache[_coercion_cache_num] = current;
         _coercion_cache_num++;
     }
-    else {
+    else
+#endif
+    {
         PyMem_Free(current);
     }
     return next;

From b3b5109100e5880ce03ca93a112b25bca6578ddb Mon Sep 17 00:00:00 2001
From: Nathan Goldbaum <nathan.goldbaum@gmail.com>
Date: Thu, 18 Apr 2024 09:09:08 -0600
Subject: [PATCH 2/3] TST: add a test in a new test_multithreading module

---
 numpy/_core/tests/test_multithreading.py | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 numpy/_core/tests/test_multithreading.py

diff --git a/numpy/_core/tests/test_multithreading.py b/numpy/_core/tests/test_multithreading.py
new file mode 100644
index 000000000000..0e35408ef6b2
--- /dev/null
+++ b/numpy/_core/tests/test_multithreading.py
@@ -0,0 +1,15 @@
+import concurrent.futures
+
+import numpy as np
+
+
+def test_parallel_errstate_creation():
+    # if the coercion cache is enabled and not thread-safe, creating
+    # RandomState instances simultaneously leads to a data race
+    def func(seed):
+        np.random.RandomState(seed)
+
+    with concurrent.futures.ThreadPoolExecutor(max_workers=8) as tpe:
+        futures = [tpe.submit(func, i) for i in range(500)]
+        for f in futures:
+            f.result()

From 1d976fc448cedc1033f9f928daed5fdeac7738ea Mon Sep 17 00:00:00 2001
From: Nathan Goldbaum <nathan.goldbaum@gmail.com>
Date: Thu, 18 Apr 2024 10:06:14 -0600
Subject: [PATCH 3/3] TST: skip multithreading tests on WASM

---
 numpy/_core/tests/test_multithreading.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/numpy/_core/tests/test_multithreading.py b/numpy/_core/tests/test_multithreading.py
index 0e35408ef6b2..8999a18a39ff 100644
--- a/numpy/_core/tests/test_multithreading.py
+++ b/numpy/_core/tests/test_multithreading.py
@@ -1,6 +1,12 @@
 import concurrent.futures
 
 import numpy as np
+import pytest
+
+from numpy.testing import IS_WASM
+
+if IS_WASM:
+    pytest.skip(allow_module_level=True, reason="no threading support in wasm")
 
 
 def test_parallel_errstate_creation():