Process aliases

Signed-off-by: Mateusz Front <mateusz.front@swmansion.com>

Author: mat-hek

libs/estdlib/src/erlang.erl

@@ -99,6 +99,7 @@
     make_ref/0,
     send/2,
     monitor/2,
+    monitor/3,
     demonitor/1,
     demonitor/2,
     exit/1,
@@ -133,7 +134,9 @@
     dist_ctrl_put_data/2,
     unique_integer/0,
     unique_integer/1,
-    raise/3
+    raise/3,
+    alias/0,
+    unalias/1
 ]).
 
 -export_type([
@@ -177,7 +180,8 @@
     | {max_heap_size, pos_integer()}
     | {atomvm_heap_growth, atomvm_heap_growth_strategy()}
     | link
-    | monitor.
+    | monitor
+    | {monitor, [monitor_option()]}.
 
 -type send_destination() ::
     pid()
@@ -203,6 +207,8 @@
 -type raise_stacktrace() ::
     [{module(), atom(), arity() | [term()]} | {function(), arity() | [term()]}] | stacktrace().
 
+-type monitor_option() :: {'alias', 'explicit_unalias' | 'demonitor' | 'reply_demonitor'}.
+
 %%-----------------------------------------------------------------------------
 %% @param   Time time in milliseconds after which to send the timeout message.
 %% @param   Dest Pid or server name to which to send the timeout message.
@@ -1167,6 +1173,28 @@ send(_Target, _Message) ->
 monitor(_Type, _PidOrPort) ->
     erlang:nif_error(undefined).
 
+%%-----------------------------------------------------------------------------
+%% @param   Type        type of monitor to create
+%% @param   PidOrPort   pid or port of the object to monitor
+%% @param   Options     monitor options
+%% @returns a monitor reference
+%% @doc     Creates a monitor and allows passing additional options.
+%%          Currently, only the `{alias, AliasMode}' option is supported. Passing it
+%%          makes the monitor also an alias on the calling process (see `alias/0').
+%%          `AliasMode' defines the behaviour of the alias:
+%%          - explicit_unalias - the alias can be only removed with `unalias/1',
+%%          - demonitor - the alias is also removed when `demonitor/1' is called
+%%                        on the monitor,
+%%          - reply_demonitor - the alias is also removed after a first message
+%%                              is sent via it.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec monitor
+    (Type :: process, Pid :: pid() | atom(), [monitor_option()]) -> reference();
+    (Type :: port, Port :: port() | atom(), [monitor_option()]) -> reference().
+monitor(_Type, _PidOrPort, _Options) ->
+    erlang:nif_error(undefined).
+
 %%-----------------------------------------------------------------------------
 %% @param   Monitor reference of monitor to remove
 %% @returns `true'
@@ -1578,3 +1606,25 @@ nif_error(_Reason) ->
     no_return().
 raise(_Class, _Reason, _Stacktrace) ->
     erlang:nif_error(undefined).
+
+%%-----------------------------------------------------------------------------
+%% @returns A reference aliasing the calling process.
+%% @doc     Creates an alias for the callling process. The alias can be used
+%%          to send messages to the process like the PID. The alias can also be
+%%          created along with a monitor - see `monitor/3'. The alias can be
+%%          removed by calling `unalias/1'.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec alias() -> Alias when Alias :: reference().
+alias() ->
+    erlang:nif_error(undefined).
+
+%%-----------------------------------------------------------------------------
+%% @param   Alias the alias to be removed.
+%% @returns `true' if alias was removed, `false' if it was not found
+%% @doc     Removes process alias. See `alias/0' for more information.
+%% @end
+%%-----------------------------------------------------------------------------
+-spec unalias(Alias) -> boolean() when Alias :: reference().
+unalias(_Alias) ->
+    erlang:nif_error(undefined).

src/libAtomVM/context.c

@@ -260,6 +260,7 @@ void context_destroy(Context *ctx)
                 case CONTEXT_MONITOR_MONITORED_LOCAL:
                 case CONTEXT_MONITOR_MONITORING_LOCAL:
                 case CONTEXT_MONITOR_MONITORING_LOCAL_REGISTEREDNAME:
+                case CONTEXT_MONITOR_ALIAS:
                     UNREACHABLE();
             }
         }
@@ -774,15 +775,15 @@ static struct Monitor *context_monitors_handle_terminate(Context *ctx)
                 Context *target = globalcontext_get_process_nolock(glb, local_process_id);
                 // Target cannot be NULL as we processed Demonitor signals
                 assert(target != NULL);
-                int required_terms = REF_SIZE + TUPLE_SIZE(5);
+                int required_terms = TERM_BOXED_PROCESS_REF_SIZE + TUPLE_SIZE(5);
                 if (UNLIKELY(memory_ensure_free(ctx, required_terms) != MEMORY_GC_OK)) {
                     // TODO: handle out of memory here
                     fprintf(stderr, "Cannot handle out of memory.\n");
                     globalcontext_get_process_unlock(glb, target);
                     AVM_ABORT();
                 }
                 // Prepare the message on ctx's heap which will be freed afterwards.
-                term ref = term_from_ref_ticks(monitored_monitor->ref_ticks, &ctx->heap);
+                term ref = term_make_process_reference(target->process_id, monitored_monitor->ref_ticks, &ctx->heap);
 
                 term port_or_process = term_pid_or_port_from_context(ctx);
                 term port_or_process_atom
@@ -799,6 +800,9 @@ static struct Monitor *context_monitors_handle_terminate(Context *ctx)
                 free(monitor);
                 break;
             }
+            case CONTEXT_MONITOR_ALIAS: {
+                free(monitor);
+            }
         }
     }
     return result;
@@ -869,6 +873,19 @@ struct Monitor *monitor_registeredname_monitor_new(int32_t monitor_process_id, t
     return &monitor->monitor;
 }
 
+struct Monitor *monitor_alias_new(uint64_t ref_ticks, enum ContextMonitorAliasType alias_type)
+{
+    struct MonitorAlias *monitor = malloc(sizeof(struct MonitorAlias));
+    if (IS_NULL_PTR(monitor)) {
+        return NULL;
+    }
+    monitor->monitor.monitor_type = CONTEXT_MONITOR_ALIAS;
+    monitor->ref_ticks = ref_ticks;
+    monitor->alias_type = alias_type;
+
+    return &monitor->monitor;
+}
+
 struct Monitor *monitor_resource_monitor_new(void *resource, uint64_t ref_ticks)
 {
     struct ResourceContextMonitor *monitor = malloc(sizeof(struct ResourceContextMonitor));
@@ -920,6 +937,16 @@ bool context_add_monitor(Context *ctx, struct Monitor *new_monitor)
                     }
                     break;
                 }
+                case CONTEXT_MONITOR_ALIAS: {
+                    struct MonitorAlias *new_alias_monitor = CONTAINER_OF(new_monitor, struct MonitorAlias, monitor);
+                    struct MonitorAlias *existing_alias_monitor = CONTAINER_OF(existing, struct MonitorAlias, monitor);
+
+                    if (UNLIKELY(existing_alias_monitor->alias_type == new_alias_monitor->alias_type && existing_alias_monitor->ref_ticks == new_alias_monitor->ref_ticks)) {
+                        free(new_monitor);
+                        return false;
+                    }
+                    break;
+                }
                 case CONTEXT_MONITOR_RESOURCE: {
                     struct ResourceContextMonitor *new_resource_monitor = CONTAINER_OF(new_monitor, struct ResourceContextMonitor, monitor);
                     struct ResourceContextMonitor *existing_resource_monitor = CONTAINER_OF(existing, struct ResourceContextMonitor, monitor);
@@ -1053,6 +1080,11 @@ void context_unlink_ack(Context *ctx, term link_pid, uint64_t unlink_id)
 
 void context_demonitor(Context *ctx, uint64_t ref_ticks)
 {
+    struct MonitorAlias *alias = context_find_alias(ctx, ref_ticks);
+    if (alias != NULL && alias->alias_type != ContextMonitorAliasExplicitUnalias) {
+        context_unalias(alias);
+    }
+
     struct ListHead *item;
     LIST_FOR_EACH (item, &ctx->monitors_head) {
         struct Monitor *monitor = GET_LIST_ENTRY(item, struct Monitor, monitor_list_head);
@@ -1086,11 +1118,36 @@ void context_demonitor(Context *ctx, uint64_t ref_ticks)
             }
             case CONTEXT_MONITOR_LINK_LOCAL:
             case CONTEXT_MONITOR_LINK_REMOTE:
+            case CONTEXT_MONITOR_ALIAS:
                 break;
         }
     }
 }
 
+struct MonitorAlias *context_find_alias(Context *ctx, uint64_t ref_ticks)
+{
+    struct ListHead *item;
+    LIST_FOR_EACH (item, &ctx->monitors_head) {
+        struct Monitor *monitor = GET_LIST_ENTRY(item, struct Monitor, monitor_list_head);
+        if (monitor->monitor_type == CONTEXT_MONITOR_ALIAS) {
+            struct MonitorAlias *alias_monitor = CONTAINER_OF(monitor, struct MonitorAlias, monitor);
+            if (alias_monitor->ref_ticks == ref_ticks) {
+                return alias_monitor;
+            }
+        }
+    }
+
+    return NULL;
+}
+
+void context_unalias(struct MonitorAlias *alias)
+{
+    TERM_DEBUG_ASSERT(alias != NULL);
+    struct Monitor *monitor = &alias->monitor;
+    list_remove(&monitor->monitor_list_head);
+    free(monitor);
+}
+
 term context_get_monitor_pid(Context *ctx, uint64_t ref_ticks, bool *is_monitoring)
 {
     struct ListHead *item;
@@ -1117,6 +1174,7 @@ term context_get_monitor_pid(Context *ctx, uint64_t ref_ticks, bool *is_monitori
             case CONTEXT_MONITOR_LINK_LOCAL:
             case CONTEXT_MONITOR_LINK_REMOTE:
             case CONTEXT_MONITOR_RESOURCE:
+            case CONTEXT_MONITOR_ALIAS:
                 break;
         }
     }
@@ -1246,6 +1304,12 @@ COLD_FUNC void context_dump(Context *ctx)
                 fprintf(stderr, "\n");
                 break;
             }
+            case CONTEXT_MONITOR_ALIAS: {
+                struct MonitorLocalMonitor *monitored_monitor = CONTAINER_OF(monitor, struct MonitorLocalMonitor, monitor);
+                fprintf(stderr, "has alias ref=%lu", (long unsigned) monitored_monitor->ref_ticks);
+                fprintf(stderr, "\n");
+                break;
+            }
             case CONTEXT_MONITOR_MONITORED_LOCAL: {
                 struct MonitorLocalMonitor *monitored_monitor = CONTAINER_OF(monitor, struct MonitorLocalMonitor, monitor);
                 fprintf(stderr, "monitored by ");

src/libAtomVM/context.h

@@ -172,6 +172,14 @@ enum ContextMonitorType
     CONTEXT_MONITOR_RESOURCE,
     CONTEXT_MONITOR_LINK_REMOTE,
     CONTEXT_MONITOR_MONITORING_LOCAL_REGISTEREDNAME,
+    CONTEXT_MONITOR_ALIAS,
+};
+
+enum ContextMonitorAliasType
+{
+    ContextMonitorAliasExplicitUnalias,
+    ContextMonitorAliasDemonitor,
+    ContextMonitorAliasReplyDemonitor,
 };
 
 #define UNLINK_ID_LINK_ACTIVE 0x0
@@ -207,6 +215,13 @@ struct MonitorLocalRegisteredNameMonitor
     term monitor_name;
 };
 
+struct MonitorAlias
+{
+    struct Monitor monitor;
+    uint64_t ref_ticks;
+    enum ContextMonitorAliasType alias_type;
+};
+
 // The other half is called ResourceMonitor and is a linked list of resources
 struct ResourceContextMonitor
 {
@@ -512,6 +527,8 @@ struct Monitor *monitor_link_new(term link_pid);
  */
 struct Monitor *monitor_new(term monitor_pid, uint64_t ref_ticks, bool is_monitoring);
 
+struct Monitor *monitor_alias_new(uint64_t ref_ticks, enum ContextMonitorAliasType alias_type);
+
 /**
  * @brief Create a monitor on a process by registered name.
  *
@@ -577,6 +594,24 @@ void context_unlink_ack(Context *ctx, term link_pid, uint64_t unlink_id);
  */
 void context_demonitor(Context *ctx, uint64_t ref_ticks);
 
+/**
+ * @brief Find a process alias
+ * @details Called within the process only
+ *
+ * @param ctx the context being executed
+ * @param ref_ticks reference of the alias to remove
+ * @return found alias or NULL
+ */
+struct MonitorAlias *context_find_alias(Context *ctx, uint64_t ref_ticks);
+
+/**
+ * @brief Remove an alias of a process
+ * @details Called within the process only
+ *
+ * @param alias The alias to remove, can be obtained using context_find_alias
+ */
+void context_unalias(struct MonitorAlias *alias);
+
 /**
  * @brief Get target of a monitor.
  *

src/libAtomVM/defaultatoms.def

@@ -211,3 +211,9 @@ X(JIT_X86_64_ATOM, "\xA", "jit_x86_64")
 X(JIT_AARCH64_ATOM, "\xB", "jit_aarch64")
 X(JIT_ARMV6M_ATOM, "\xA", "jit_armv6m")
 X(JIT_RISCV32_ATOM, "\xB", "jit_riscv32")
+
+X(ALIAS_ATOM, "\x5", "alias")
+X(DEMONITOR_ATOM, "\x9", "demonitor")
+X(EXPLICIT_UNALIAS_ATOM, "\x10", "explicit_unalias")
+X(REPLY_DEMONITOR_ATOM, "\xF", "reply_demonitor")
+X(TAG_ATOM, "\x3", "tag")

src/libAtomVM/externalterm.c

@@ -492,6 +492,8 @@ static int serialize_term(uint8_t *buf, term t, GlobalContext *glb)
         uint32_t len;
         if (term_is_resource_reference(t)) {
             len = 4;
+        } else if (term_is_process_reference(t)) {
+            len = 3;
         } else {
             len = 2;
         }
@@ -513,6 +515,15 @@ static int serialize_term(uint8_t *buf, term t, GlobalContext *glb)
                 WRITE_64_UNALIGNED(buf + k + 12, ((uintptr_t) serialize_ref));
             }
             return k + 20;
+        } else if (term_is_process_reference(t)) {
+            if (!IS_NULL_PTR(buf)) {
+                uint64_t ticks = term_to_ref_ticks(t);
+                uint32_t process_id = term_process_ref_to_process_id(t);
+                WRITE_32_UNALIGNED(buf + k, creation);
+                WRITE_64_UNALIGNED(buf + k + 4, ticks);
+                WRITE_32_UNALIGNED(buf + k + 12, process_id);
+            }
+            return k + 16;
         } else {
             if (!IS_NULL_PTR(buf)) {
                 uint64_t ticks = term_to_ref_ticks(t);
@@ -901,6 +912,10 @@ static term parse_external_terms(const uint8_t *external_term_buf, size_t *eterm
                 if (len == 2 && node == this_node && creation == this_creation) {
                     uint64_t ticks = ((uint64_t) data[0]) << 32 | data[1];
                     return term_from_ref_ticks(ticks, heap);
+                } else if (len == 3 && node == this_node && creation == this_creation) {
+                    uint64_t ticks = ((uint64_t) data[0]) << 32 | data[1];
+                    uint32_t process_id = data[2];
+                    return term_make_process_reference(process_id, ticks, heap);
                 } else if (len == 4 && node == this_node && creation == this_creation) {
                     // This is a resource
                     uint64_t resource_type_ptr = ((uint64_t) data[0]) << 32 | data[1];