Add support for unregister/1

Closes issue atomvm#358.

Signed-off-by: Winford <dwinford@pm.me>

CHANGELOG.md

@@ -22,6 +22,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Added `erlang:is_boolean/1` Bif.
 - Added support for `esp:partition_erase_range/2`
 - Added support for `i2c:close/1`
+- Added `erlang:is_boolean/1` Bif.
+- Added support for `esp:partition_erase_range/2`
+- Added support for `i2c:close/1`
+- Added support for `unregister/1`
 
 ### Breaking Changes
 

src/libAtomVM/globalcontext.c

@@ -135,6 +135,28 @@ void globalcontext_register_process(GlobalContext *glb, int atom_index, int loca
     linkedlist_append(&glb->registered_processes, &registered_process->registered_processes_list_head);
 }
 
+bool globalcontext_unregister_process(GlobalContext *glb, int atom_index)
+{
+    if (!glb->registered_processes) {
+        return false;
+    }
+
+    struct RegisteredProcess *registered_processes = GET_LIST_ENTRY(glb->registered_processes, struct RegisteredProcess, registered_processes_list_head);
+
+    struct RegisteredProcess *p = registered_processes;
+
+    do {
+        if (p->atom_index == atom_index) {
+            linkedlist_remove(&glb->registered_processes, &p->registered_processes_list_head);
+            free(p);
+            return true;
+        }
+        p = GET_LIST_ENTRY(p->registered_processes_list_head.next, struct RegisteredProcess, registered_processes_list_head);
+    } while (p != registered_processes);
+
+    return false;
+}
+
 int globalcontext_get_registered_process(GlobalContext *glb, int atom_index)
 {
     if (!glb->registered_processes) {

src/libAtomVM/globalcontext.h

@@ -140,6 +140,15 @@ void globalcontext_register_process(GlobalContext *glb, int atom_index, int loca
  */
 int globalcontext_get_registered_process(GlobalContext *glb, int atom_index);
 
+/**
+ * @brief Unregister a process
+ *
+ * @details Unregister a process with a certain name (atom).
+ * @param glb the global context, each registered process will be globally available for that context.
+ * @param atom_index the atom table index.
+ */
+bool globalcontext_unregister_process(GlobalContext *glb, int atom_index);
+
 /**
  * @brief equivalent to globalcontext_insert_atom_maybe_copy(glb, atom_string, 0);
  */

src/libAtomVM/nifs.c

@@ -118,6 +118,7 @@ static term nif_erlang_iolist_size_1(Context *ctx, int argc, term argv[]);
 static term nif_erlang_iolist_to_binary_1(Context *ctx, int argc, term argv[]);
 static term nif_erlang_open_port_2(Context *ctx, int argc, term argv[]);
 static term nif_erlang_register_2(Context *ctx, int argc, term argv[]);
+static term nif_erlang_unregister_1(Context *ctx, int argc, term argv[]);
 static term nif_erlang_send_2(Context *ctx, int argc, term argv[]);
 static term nif_erlang_setelement_3(Context *ctx, int argc, term argv[]);
 static term nif_erlang_spawn(Context *ctx, int argc, term argv[]);
@@ -364,6 +365,12 @@ static const struct Nif register_nif =
     .nif_ptr = nif_erlang_register_2
 };
 
+static const struct Nif unregister_nif =
+{
+    .base.type = NIFFunctionType,
+    .nif_ptr = nif_erlang_unregister_1
+};
+
 static const struct Nif spawn_nif =
 {
     .base.type = NIFFunctionType,
@@ -762,13 +769,10 @@ static term nif_erlang_register_2(Context *ctx, int argc, term argv[])
     int atom_index = term_to_atom_index(reg_name_term);
     int32_t pid = term_to_local_process_id(pid_or_port_term);
 
-    // pid must be existing, not already registered.
-    if (UNLIKELY(globalcontext_get_process(ctx->global, pid) == NULL)){
-        RAISE_ERROR(BADARG_ATOM);
-    } else if (UNLIKELY(globalcontext_get_registered_process(ctx->global, atom_index) != 0)) {
-        RAISE_ERROR(BADARG_ATOM);
-    // reg_name_term must not be the atom undefined.
-    } else if (UNLIKELY(atom_index == UNDEFINED_ATOM_INDEX)) {
+    // pid must be existing, not already registered, and not the atom undefined.
+    if (UNLIKELY(globalcontext_get_process(ctx->global, pid) == NULL) ||
+        globalcontext_get_registered_process(ctx->global, atom_index) != 0 ||
+        reg_name_term == UNDEFINED_ATOM){
         RAISE_ERROR(BADARG_ATOM);
     }
 
@@ -777,6 +781,23 @@ static term nif_erlang_register_2(Context *ctx, int argc, term argv[])
     return TRUE_ATOM;
 }
 
+static term nif_erlang_unregister_1(Context *ctx, int argc, term argv[])
+{
+    UNUSED(argc);
+
+    term reg_name_term = argv[0];
+    VALIDATE_VALUE(reg_name_term, term_is_atom);
+
+    int atom_index = term_to_atom_index(reg_name_term);
+
+    bool unregistered = globalcontext_unregister_process(ctx->global, atom_index);
+    if (UNLIKELY(!unregistered)) {
+        RAISE_ERROR(BADARG_ATOM);
+    }
+
+    return TRUE_ATOM;
+}
+
 static term nif_erlang_whereis_1(Context *ctx, int argc, term argv[])
 {
     UNUSED(argc);

src/libAtomVM/nifs.gperf

@@ -73,6 +73,7 @@ erlang:monitor/2, &monitor_nif
 erlang:demonitor/1, &demonitor_nif
 erlang:is_process_alive/1, &is_process_alive_nif
 erlang:register/2, &register_nif
+erlang:unregister/1, &unregister_nif
 erlang:send/2, &send_nif
 erlang:setelement/3, &setelement_nif
 erlang:spawn/1, &spawn_fun_nif