Unregister processes when they die

Adds the function `globalcontext_maybe_unregister_process_id` to globalcontext.c
to allow removing the appropriate entry from the registered atoms table when the
associated context is destroyed.

Signed-off-by: Winford <winford@object.stream>

src/libAtomVM/context.c

@@ -110,6 +110,9 @@ void context_destroy(Context *ctx)
     // Another process can get an access to our mailbox until this point.
     synclist_remove(&ctx->global->processes_table, &ctx->processes_table_head);
 
+    // Ensure process is not registered
+    globalcontext_maybe_unregister_process_id(ctx->global, ctx->process_id);
+
     // When monitor message is sent, process is no longer in the table.
     context_monitors_handle_terminate(ctx);
 
@@ -135,6 +138,7 @@ void context_destroy(Context *ctx)
     if (ctx->platform_data) {
         free(ctx->platform_data);
     }
+
     free(ctx);
 }
 

src/libAtomVM/globalcontext.c

@@ -316,6 +316,23 @@ bool globalcontext_unregister_process(GlobalContext *glb, int atom_index)
     return false;
 }
 
+bool globalcontext_maybe_unregister_process_id(GlobalContext *glb, int target_process_id)
+{
+    struct ListHead *registered_processes_list = synclist_wrlock(&glb->registered_processes);
+    struct ListHead *item;
+    LIST_FOR_EACH (item, registered_processes_list) {
+        const struct RegisteredProcess *registered_process = GET_LIST_ENTRY(item, struct RegisteredProcess, registered_processes_list_head);
+        if (registered_process->local_process_id == target_process_id) {
+            list_remove(item);
+            free(item);
+            synclist_unlock(&glb->registered_processes);
+            return true;
+        }
+    }
+    synclist_unlock(&glb->registered_processes);
+    return false;
+}
+
 int globalcontext_get_registered_process(GlobalContext *glb, int atom_index)
 {
     struct ListHead *registered_processes_list = synclist_rdlock(&glb->registered_processes);

src/libAtomVM/globalcontext.h

@@ -237,6 +237,17 @@ int globalcontext_get_registered_process(GlobalContext *glb, int atom_index);
  */
 bool globalcontext_unregister_process(GlobalContext *glb, int atom_index);
 
+/**
+ * @brief Remove entry from registered atoms by process id
+ *
+ * @details Unregister a process with a certain process id. This is used when a process dies to ensure
+ * the process is not registered and remove it from the registered atoms table if it is.
+ * @param glb the global context, each registered process will be globally available for that context.
+ * @param process_id the process id of the entry to remove.
+ * @returns \c true if the process was unregistered, \c false otherwise
+ */
+bool globalcontext_maybe_unregister_process_id(GlobalContext *glb, int process_id);
+
 /**
  * @brief equivalent to globalcontext_insert_atom_maybe_copy(glb, atom_string, 0);
  */

tests/erlang_tests/CMakeLists.txt

@@ -87,6 +87,7 @@ compile_erlang(match)
 compile_erlang(if_test)
 compile_erlang(sleep)
 compile_erlang(hello_world)
+compile_erlang(whereis_dead_process)
 compile_erlang(whereis_fail)
 compile_erlang(register_unregister)
 compile_erlang(try_noerror)
@@ -518,6 +519,7 @@ add_custom_target(erlang_test_modules DEPENDS
     if_test.beam
     sleep.beam
     hello_world.beam
+    whereis_dead_process.beam
     whereis_fail.beam
     register_unregister.beam
     try_noerror.beam

tests/erlang_tests/whereis_dead_process.erl

@@ -0,0 +1,32 @@
+%
+% This file is part of AtomVM.
+%
+% Copyright 2023 Winford (Uncle Grumpy) <winford@object.stream>
+%
+% Licensed under the Apache License, Version 2.0 (the "License");
+% you may not use this file except in compliance with the License.
+% You may obtain a copy of the License at
+%
+%    http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS,
+% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+% See the License for the specific language governing permissions and
+% limitations under the License.
+%
+% SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
+%
+
+-module(whereis_dead_process).
+
+-export([start/0]).
+
+start() ->
+    spawn(fun() -> register(foo, self()) end),
+    result_to_int(whereis(foo)).
+
+result_to_int(undefined) ->
+    0;
+result_to_int(_) ->
+    1.

tests/test.c

@@ -112,6 +112,7 @@ struct Test tests[] = {
     TEST_CASE_EXPECTED(match, 5),
     TEST_CASE_EXPECTED(if_test, 5),
     TEST_CASE(sleep),
+    TEST_CASE(whereis_dead_process),
     TEST_CASE_EXPECTED(whereis_fail, 2),
     TEST_CASE_EXPECTED(try_noerror, 1),
     TEST_CASE_EXPECTED(catch_badmatch, 1),