Merge branch 'sverk/deprecate-nif-reload'

* sverk/deprecate-nif-reload:
  erts: Deprecate the NIF reload mechanism

OTP-9771

2 files changed, 30 insertions, 16 deletions

diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml
index 8daa67aa87..5fc6508aad 100644
--- a/erts/doc/src/erl_nif.xml
+++ b/erts/doc/src/erl_nif.xml
@@ -136,9 +136,7 @@ ok
      then retrieved by calling <seealso marker="#enif_priv_data">enif_priv_data</seealso>.</p>
     <p>There is no way to explicitly unload a NIF library. A library will be
      automatically unloaded when the module code that it belongs to is purged
-     by the code server. A NIF library will also be unloaded if it is replaced
-     by another version of the library by a second call to
-     <c>erlang:load_nif/2</c> from the same module code.</p> 
+     by the code server.</p> 
   </description>
   <section>
   <title>FUNCTIONALITY</title>
@@ -308,21 +306,9 @@ ok
            initialization is needed.</p> 
        </item>
 
-      <tag><marker id="reload"/>int (*reload)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag>
-       <item><p><c>reload</c> is called when the NIF library is loaded
-        and there is already a previously loaded library for this
-        module code.</p>
-        <p>Works the same as <c>load</c>. The only difference is that
-        <c>*priv_data</c> already contains the value set by the
-        previous call to <c>load</c> or <c>reload</c>.</p>
-        <p>The library will fail to load if <c>reload</c> returns
-           anything other than 0 or if <c>reload</c> is NULL.</p> 
-      </item>
-
       <tag><marker id="upgrade"/>int (*upgrade)(ErlNifEnv* env, void** priv_data, void** old_priv_data, ERL_NIF_TERM load_info)</tag>
        <item><p><c>upgrade</c> is called when the NIF library is loaded
-        and there is no previously loaded library for this module
-        code, BUT there is old code of this module with a loaded NIF library.</p>
+        and there is old code of this module with a loaded NIF library.</p>
         <p>Works the same as <c>load</c>. The only difference is that
         <c>*old_priv_data</c> already contains the value set by the
          last call to <c>load</c> or <c>reload</c> for the old module
@@ -339,6 +325,23 @@ ok
        called for a replaced library as a consequence of <c>reload</c>.</p>
       </item>
 
+      <tag><marker id="reload"/>int (*reload)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag>
+     <note><p>The reload mechanism is <em>deprecated</em>. It was only intended
+     as a development feature. Do not use it as an upgrade method for
+     live production systems. It might be removed in future releases. Be sure
+     to pass <c>reload</c> as <c>NULL</c> to <seealso marker="#ERL_NIF_INIT">ERL_NIF_INIT</seealso>
+     to disable it when not used.</p>
+     </note>
+       <item><p><c>reload</c> is called when the NIF library is loaded
+        and there is already a previously loaded library for this
+        module code.</p>
+        <p>Works the same as <c>load</c>. The only difference is that
+        <c>*priv_data</c> already contains the value set by the
+        previous call to <c>load</c> or <c>reload</c>.</p>
+        <p>The library will fail to load if <c>reload</c> returns
+           anything other than 0 or if <c>reload</c> is NULL.</p> 
+      </item>
+
     </taglist>
   </section>
 
diff --git a/erts/emulator/beam/erl_nif.c b/erts/emulator/beam/erl_nif.c
index 143f631f58..58a09986d2 100644
--- a/erts/emulator/beam/erl_nif.c
+++ b/erts/emulator/beam/erl_nif.c
@@ -1507,6 +1507,7 @@ BIF_RETTYPE load_nif_2(BIF_ALIST_2)
     Eterm ret = am_ok;
     int veto;
     struct erl_module_nif* lib = NULL;
+    int reload_warning = 0;
 
     len = list_length(BIF_ARG_1);
     if (len < 0) {
@@ -1646,6 +1647,7 @@ BIF_RETTYPE load_nif_2(BIF_ALIST_2)
 	else {
 	    mod->nif->entry = NULL; /* to prevent 'unload' callback */
 	    erts_unload_nif(mod->nif);
+	    reload_warning = 1;
 	}
     }
     else {
@@ -1714,6 +1716,15 @@ BIF_RETTYPE load_nif_2(BIF_ALIST_2)
     erts_smp_thr_progress_unblock();
     erts_smp_proc_lock(BIF_P, ERTS_PROC_LOCK_MAIN);
     erts_free(ERTS_ALC_T_TMP, lib_name);
+
+    if (reload_warning) {
+	erts_dsprintf_buf_t* dsbufp = erts_create_logger_dsbuf();
+	erts_dsprintf(dsbufp,
+		      "Repeated calls to erlang:load_nif from module '%T'.\n\n"
+		      "The NIF reload mechanism is deprecated and must not "
+		      "be used in production systems.\n", mod_atom);
+	erts_send_warning_to_logger(BIF_P->group_leader, dsbufp);
+    }
     BIF_RET(ret);
 }