fixes #1572 nng creates too many threads

This further limits some of the thread counts, but principally it
offers a new runtime facility, nng_init_set_parameter(), which can
be used to set certain runtime parameters on the number of threads,
provided it is called before the rest of application start up.

This facility is quite intentionally "undocumented", at least for now,
as we want to limit our commitment to it.  Still this should be helpful
for applications that need to reduce the number of threads that are
created.

1 files changed, 99 insertions, 1 deletions

diff --git a/src/core/init.c b/src/core/init.c
index f2195bcb..8f2e1056 100644
--- a/src/core/init.c
+++ b/src/core/init.c
@@ -1,5 +1,5 @@
 //
-// Copyright 2023 Staysail Systems, Inc. <info@staysail.tech>
+// Copyright 2024 Staysail Systems, Inc. <info@staysail.tech>
 // Copyright 2018 Capitar IT Group BV <info@capitar.com>
 //
 // This software is supplied under the terms of the MIT License, a
@@ -54,10 +54,107 @@ nni_init(void)
 	return (nni_plat_init(nni_init_helper));
 }
 
+// accessing the list of parameters
+typedef struct nni_init_param {
+	nni_list_node      node;
+	nng_init_parameter param;
+	uint64_t           value;
+#ifdef NNG_TEST_LIB
+	uint64_t           effective;
+#endif
+} nni_init_param;
+
+static nni_list nni_init_params =
+    NNI_LIST_INITIALIZER(nni_init_params, nni_init_param, node);
+
+void
+nni_init_set_param(nng_init_parameter p, uint64_t value)
+{
+	if (nni_inited) {
+		// this is paranoia -- if some library code started already
+		// then we cannot safely change parameters, and modifying the
+		// list is not thread safe.
+		return;
+	}
+	nni_init_param *item;
+	NNI_LIST_FOREACH (&nni_init_params, item) {
+		if (item->param == p) {
+			item->value = value;
+			return;
+		}
+	}
+	if ((item = NNI_ALLOC_STRUCT(item)) != NULL) {
+		item->param = p;
+		item->value = value;
+		nni_list_append(&nni_init_params, item);
+	}
+}
+
+uint64_t
+nni_init_get_param(nng_init_parameter p, uint64_t default_value)
+{
+	nni_init_param *item;
+	NNI_LIST_FOREACH (&nni_init_params, item) {
+		if (item->param == p) {
+			return (item->value);
+		}
+	}
+	return (default_value);
+}
+
+void
+nni_init_set_effective(nng_init_parameter p, uint64_t value)
+{
+#ifdef NNG_TEST_LIB
+	nni_init_param *item;
+	NNI_LIST_FOREACH (&nni_init_params, item) {
+		if (item->param == p) {
+			item->effective = value;
+			return;
+		}
+	}
+	if ((item = NNI_ALLOC_STRUCT(item)) != NULL) {
+		item->param = p;
+		item->effective = value;
+		nni_list_append(&nni_init_params, item);
+	}
+#else
+	NNI_ARG_UNUSED(p);
+	NNI_ARG_UNUSED(value);
+#endif
+}
+
+#ifdef NNG_TEST_LIB
+uint64_t
+nni_init_get_effective(nng_init_parameter p)
+{
+	nni_init_param *item;
+	NNI_LIST_FOREACH (&nni_init_params, item) {
+		if (item->param == p) {
+			return (item->effective);
+		}
+	}
+	return ((uint64_t)-1);
+}
+#endif
+
+
+static void
+nni_init_params_fini(void)
+{
+	nni_init_param *item;
+	while ((item = nni_list_first(&nni_init_params)) != NULL) {
+		nni_list_remove(&nni_init_params, item);
+		NNI_FREE_STRUCT(item);
+	}
+}
+
 void
 nni_fini(void)
 {
 	if (!nni_inited) {
+		// make sure we discard parameters even if we didn't startup
+		nni_init_params_fini();
 		return;
 	}
 	nni_sp_tran_sys_fini();
@@ -67,6 +164,7 @@ nni_fini(void)
 	nni_taskq_sys_fini();
 	nni_reap_sys_fini(); // must be before timer and aio (expire)
 	nni_id_map_sys_fini();
+	nni_init_params_fini();
 
 	nni_plat_fini();
 	nni_inited = false;