Merge pull request numpy#26750 from ngoldbaum/lapacklite-locking

ENH: Add locking to umath_linalg if no lapack is detected at build time

Author: rgommers

doc/release/upcoming_changes/26750.improvement.rst

@@ -0,0 +1,12 @@
+`lapack_lite` is now thread safe
+--------------------------------
+
+NumPy provides a minimal low-performance version of LAPACK named ``lapack_lite``
+that can be used if no BLAS/LAPACK system is detected at build time.
+
+Until now, ``lapack_lite`` was not thread safe. Single-threaded use cases did
+not hit any issues, but running linear algebra operations in multiple threads
+could lead to errors, incorrect results, or seg faults due to data races.
+
+We have added a global lock, serializing access to ``lapack_lite`` in multiple
+threads.

numpy/_core/config.h.in

@@ -108,6 +108,8 @@
 #mesondefine HAVE_LDOUBLE_IBM_DOUBLE_DOUBLE_LE
 #mesondefine HAVE_LDOUBLE_IBM_DOUBLE_DOUBLE_BE
 
+#mesondefine HAVE_EXTERNAL_LAPACK
+
 #ifndef __cplusplus
 /* #undef inline */
 #endif

numpy/_core/meson.build

@@ -506,6 +506,10 @@ if cc.has_function_attribute('visibility:hidden') and host_machine.system() != '
 endif
 cdata.set('NPY_VISIBILITY_HIDDEN', visibility_hidden)
 
+# if not set, we're using lapack_lite
+if have_lapack
+  cdata.set10('HAVE_EXTERNAL_LAPACK', have_lapack)
+endif
 
 config_h = configure_file(
   input: 'config.h.in',

numpy/_core/tests/test_multithreading.py

@@ -71,3 +71,16 @@ def func(count):
             (alarge + blarge) - 2
 
     run_threaded(func, 100, pass_count=True)
+
+
+def test_eigvalsh_thread_safety():
+    # if lapack isn't thread safe this will randomly segfault or error
+    # see gh-24512
+    rng = np.random.RandomState(873699172)
+    matrices = (
+        rng.random((5, 10, 10, 3, 3)),
+        rng.random((5, 10, 10, 3, 3)),
+    )
+
+    run_threaded(lambda i: np.linalg.eigvalsh(matrices[i]), 2,
+                 pass_count=True)