Try #704:

libs/pika/init_runtime/include/pika/init_runtime/init_runtime.hpp

@@ -143,6 +143,7 @@ namespace pika {
         init_params const& params = init_params());
     PIKA_EXPORT int finalize(error_code& ec = throws);
     PIKA_EXPORT int stop(error_code& ec = throws);
+    PIKA_EXPORT int wait(error_code& ec = throws);
     PIKA_EXPORT int suspend(error_code& ec = throws);
     PIKA_EXPORT int resume(error_code& ec = throws);
 }    // namespace pika

libs/pika/init_runtime/src/init_runtime.cpp

@@ -217,6 +217,21 @@ namespace pika {
         return result;
     }
 
+    int wait(error_code& ec)
+    {
+        runtime* rt = get_runtime_ptr();
+        if (nullptr == rt)
+        {
+            PIKA_THROWS_IF(ec, pika::error::invalid_status, "pika::wait",
+                "the runtime system is not active (did you already call pika::stop?)");
+            return -1;
+        }
+
+        rt->get_thread_manager().wait();
+
+        return 0;
+    }
+
     int suspend(error_code& ec)
     {
         if (threads::detail::get_self_ptr())

libs/pika/init_runtime/tests/unit/CMakeLists.txt

@@ -5,7 +5,8 @@
 # file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
 set(tests
-    config_entry const_args_init finalize_non_pika_thread scoped_finalize
+    config_entry const_args_init finalize_non_pika_thread pika_wait
+    scoped_finalize
     # shutdown_suspended_thread # Disabled due to unavailable timed suspension
 )
 

libs/pika/init_runtime/tests/unit/pika_wait.cpp

@@ -0,0 +1,58 @@
+//  Copyright (c) 2023 ETH Zurich
+//
+//  SPDX-License-Identifier: BSL-1.0
+//  Distributed under the Boost Software License, Version 1.0. (See accompanying
+//  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// This test checks that the runtime takes into account suspended threads before
+// initiating full shutdown.
+
+#include <pika/execution.hpp>
+#include <pika/init.hpp>
+#include <pika/runtime/thread_pool_helpers.hpp>
+#include <pika/testing.hpp>
+
+#include <cstddef>
+
+namespace ex = pika::execution::experimental;
+namespace tt = pika::this_thread::experimental;
+
+void test_wait()
+{
+    for (std::size_t i = 0; i < 1000; ++i)
+    {
+        ex::execute(ex::thread_pool_scheduler{}, [] {});
+    }
+
+    pika::wait();
+
+    if (pika::threads::detail::get_self_ptr())
+    {
+        PIKA_TEST_EQ(pika::threads::get_thread_count(), 1);
+    }
+    else
+    {
+        PIKA_TEST_EQ(pika::threads::get_thread_count(), 0);
+    }
+}
+
+int main(int argc, char** argv)
+{
+    pika::start(nullptr, argc, argv);
+
+    // Test outside the runtime
+    test_wait();
+
+    // Test in a pika thread
+    tt::sync_wait(ex::schedule(ex::thread_pool_scheduler()) | ex::then(test_wait));
+
+    // Test in a stackless pika thread
+    tt::sync_wait(ex::schedule(ex::with_stacksize(
+                      ex::thread_pool_scheduler(), pika::execution::thread_stacksize::nostack)) |
+        ex::then(test_wait));
+
+    pika::finalize();
+    pika::stop();
+
+    return 0;
+}