BUG: avoid deadlocks with C++ shared mutex in dispatch cache

numpy · charris · Mar 24, 2025 · Mar 24, 2025 · Mar 24, 2025 · 37985a2a900a304ab102fdd692f4ad3920fd797e
commit 37985a2a900a304ab102fdd692f4ad3920fd797e
diff --git a/numpy/_core/src/umath/dispatching.cpp b/numpy/_core/src/umath/dispatching.cpp
@@ -912,7 +912,9 @@ promote_and_get_info_and_ufuncimpl_with_locking(
        npy_bool legacy_promotion_is_possible)
 {
    std::shared_mutex *mutex = ((std::shared_mutex *)((PyArrayIdentityHash *)ufunc->_dispatch_cache)->mutex);
+    NPY_BEGIN_ALLOW_THREADS
    mutex->lock_shared();
+    NPY_END_ALLOW_THREADS
    PyObject *info = PyArrayIdentityHash_GetItem(
            (PyArrayIdentityHash *)ufunc->_dispatch_cache,
            (PyObject **)op_dtypes);
@@ -926,7 +928,9 @@ promote_and_get_info_and_ufuncimpl_with_locking(

    // cache miss, need to acquire a write lock and recursively calculate the
    // correct dispatch resolution
+    NPY_BEGIN_ALLOW_THREADS
    mutex->lock();
+    NPY_END_ALLOW_THREADS
    info = promote_and_get_info_and_ufuncimpl(ufunc,
            ops, signature, op_dtypes, legacy_promotion_is_possible);
    mutex->unlock();