Downstream next event tag (DNET), a new signal for more efficient centralized federated execution

core/federated/RTI/main.c

@@ -136,6 +136,7 @@ void usage(int argc, const char* argv[]) {
   lf_print("          clock sync attempt (default is 10). Applies to 'init' and 'on'.\n");
   lf_print("  -a, --auth Turn on HMAC authentication options.\n");
   lf_print("  -t, --tracing Turn on tracing.\n");
+  lf_print("  -d, --dnet_disabled Turn off DNET signals.\n");
 
   lf_print("Command given:");
   for (int i = 0; i < argc; i++) {
@@ -263,6 +264,8 @@ int process_args(int argc, const char* argv[]) {
       rti.authentication_enabled = true;
     } else if (strcmp(argv[i], "-t") == 0 || strcmp(argv[i], "--tracing") == 0) {
       rti.base.tracing_enabled = true;
+    } else if (strcmp(argv[i], "-d") == 0 || strcmp(argv[i], "--dnet_disabled") == 0) {
+      rti.base.dnet_disabled = true;
     } else if (strcmp(argv[i], " ") == 0) {
       // Tolerate spaces
       continue;
@@ -316,9 +319,9 @@ int main(int argc, const char* argv[]) {
   assert(rti.base.number_of_scheduling_nodes < UINT16_MAX);
 
   // Allocate memory for the federates
-  rti.base.scheduling_nodes =
-      (scheduling_node_t**)calloc(rti.base.number_of_scheduling_nodes, sizeof(scheduling_node_t*));
-  for (uint16_t i = 0; i < rti.base.number_of_scheduling_nodes; i++) {
+  int n = rti.base.number_of_scheduling_nodes;
+  rti.base.scheduling_nodes = (scheduling_node_t**)calloc(n, sizeof(scheduling_node_t*));
+  for (uint16_t i = 0; i < n; i++) {
     federate_info_t* fed_info = (federate_info_t*)calloc(1, sizeof(federate_info_t));
     initialize_federate(fed_info, i);
     rti.base.scheduling_nodes[i] = (scheduling_node_t*)fed_info;

core/federated/RTI/rti_common.h

@@ -53,17 +53,16 @@ typedef struct scheduling_node_t {
   tag_t last_granted;               // The maximum TAG that has been granted so far (or NEVER if none granted)
   tag_t last_provisionally_granted; // The maximum PTAG that has been provisionally granted (or NEVER if none granted)
   tag_t next_event;                 // Most recent NET received from the scheduling node (or NEVER if none received).
+  tag_t last_DNET;                  // Most recent DNET.
   scheduling_node_state_t state;    // State of the scheduling node.
-  uint16_t* upstream;               // Array of upstream scheduling node ids.
-  interval_t* upstream_delay;       // Minimum delay on connections from upstream scheduling nodes.
-                                    // Here, NEVER encodes no delay. 0LL is a microstep delay.
-  int num_upstream;                 // Size of the array of upstream scheduling nodes and delays.
-  uint16_t* downstream;             // Array of downstream scheduling node ids.
-  int num_downstream;               // Size of the array of downstream scheduling nodes.
-  execution_mode_t mode;            // FAST or REALTIME.
-  minimum_delay_t* min_delays;      // Array of minimum delays from upstream nodes, not including this node.
-  size_t num_min_delays;            // Size of min_delays array.
-  int flags;                        // Or of IS_IN_ZERO_DELAY_CYCLE, IS_IN_CYCLE
+  uint16_t* immediate_upstreams;    // Array of immediate upstream scheduling node ids.
+  interval_t* immediate_upstream_delays; // Minimum delay on connections from immdediate upstream scheduling nodes.
+                                         // Here, NEVER encodes no delay. 0LL is a microstep delay.
+  uint16_t num_immediate_upstreams;      // Size of the array of immediate upstream scheduling nodes and delays.
+  uint16_t* immediate_downstreams;       // Array of immediate downstream scheduling node ids.
+  uint16_t num_immediate_downstreams;    // Size of the array of immediate downstream scheduling nodes.
+  execution_mode_t mode;                 // FAST or REALTIME.
+  int flags;                             // One of IS_IN_ZERO_DELAY_CYCLE, IS_IN_CYCLE
 } scheduling_node_t;
 
 /**
@@ -76,7 +75,13 @@ typedef struct rti_common_t {
   scheduling_node_t** scheduling_nodes;
 
   // Number of scheduling nodes
-  int32_t number_of_scheduling_nodes;
+  uint16_t number_of_scheduling_nodes;
+
+  // Matrix of minimum delays between pairs of nodes.
+  // Rows represent upstream nodes and Columns represent downstream nodes.
+  // FOREVER_TAG means there is no path, and ZERO_TAG means there is no delay.
+  // This could be NULL if the matrix is not being used, so accesses should test for NULL first.
+  tag_t* min_delays;
 
   // RTI's decided stop tag for the scheduling nodes
   tag_t max_stop_tag;
@@ -87,6 +92,9 @@ typedef struct rti_common_t {
   // Boolean indicating that tracing is enabled.
   bool tracing_enabled;
 
+  // Boolean indicating that DNET is enabled.
+  bool dnet_disabled;
+
   // The RTI mutex for making thread-safe access to the shared state.
   lf_mutex_t* mutex;
 } rti_common_t;
@@ -246,34 +254,66 @@ tag_t earliest_future_incoming_message_tag(scheduling_node_t* e);
 tag_t eimt_strict(scheduling_node_t* e);
 
 /**
- * Return true if the node is in a zero-delay cycle.
+ * If necessary, update the `min_delays` and the fields that indicate cycles.
+ * These fields will be updated only if they have not been previously updated or if invalidate_min_delays
+ * has been called since they were last updated.
  * @param node The node.
  */
-bool is_in_zero_delay_cycle(scheduling_node_t* node);
+void update_min_delays();
 
 /**
- * Return true if the node is in a cycle (possibly a zero-delay cycle).
- * @param node The node.
+ * Find the tag g that is the latest tag that satisfies lf_tag_add(g, minimum_delay) < next_event_tag.
+ * This function behaves like the tag subtraction, next_event_tag - minimum_delay.
+ * minimum_delay cannot be NEVER.
+ *
+ * This function is called in function downstream_next_event_tag.
+ * @param next_event_tag The next event tag of a downstream node.
+ * @param minimum_delay The minimum delay between the target upstream node and the downstream node.
  */
-bool is_in_cycle(scheduling_node_t* node);
+tag_t get_dnet_candidate(tag_t next_event_tag, tag_t minimum_delay);
 
 /**
- * For the given scheduling node (enclave or federate), if necessary, update the `min_delays`,
- * `num_min_delays`, and the fields that indicate cycles.  These fields will be
- * updated only if they have not been previously updated or if invalidate_min_delays_upstream
- * has been called since they were last updated.
+ * @brief Determine whether the specified scheduling node is needed to receive a downstream next event tag (DNET),
+ * and, if so, return the details.
+ *
+ * This function is called upon receiving a NET from one of the specified node's downstream nodes.
+ *
+ * This function calculates the minimum tag M over
+ * all downstream scheduling nodes of the most recent NET from that node minus the "after delay" (see function
+ * get_dnet_candidate). If M is earlier than the startup tag, then set the result as the NEVER_TAG.
+ *
+ * @param node The target node that may receive a new DNET.
+ * @param node_sending_new_net_id The ID of the node that sends a new NET. If this node's new NET does not
+ * change the DNET value, we can exit this function immediately. If it does, we have to look up the target node's
+ * downstream federates to compute the exact new DNET value.
+ * @return If needed, return the tag value. Otherwise, return the NEVER_TAG.
+ */
+tag_t downstream_next_event_tag(scheduling_node_t* node, uint16_t node_sending_new_net_id);
+
+/**
+ * Notify a downstream next event tag (DNET) signal to the specified scheduling node.
+ * @param e The target node.
+ * @param tag The downstream next event tag for e.
+ */
+void notify_downstream_next_event_tag(scheduling_node_t* e, tag_t tag);
+
+/**
+ * Return true if the node is in a zero-delay cycle.
  * @param node The node.
  */
-void update_min_delays_upstream(scheduling_node_t* node);
+bool is_in_zero_delay_cycle(scheduling_node_t* node);
 
 /**
- * For the given scheduling node (enclave or federate), invalidate the `min_delays`,
- * `num_min_delays`, and the fields that indicate cycles.
- * This should be called whenever the structure of the connections upstream of the
- * given node have changed.
+ * Return true if the node is in a cycle (possibly a zero-delay cycle).
  * @param node The node.
  */
-void invalidate_min_delays_upstream(scheduling_node_t* node);
+bool is_in_cycle(scheduling_node_t* node);
+
+/**
+ * Invalidate the `min_delays`, `num_min_delays`, and the fields that indicate cycles
+ * of all nodes. This should be called whenever the structure of the connections have changed.
+ */
+void invalidate_min_delays();
 
 /**
  * Free dynamically allocated memory on the scheduling nodes and the scheduling node array itself.

core/federated/RTI/rti_local.c

@@ -53,9 +53,9 @@ void initialize_local_rti(environment_t* envs, int num_envs) {
     rti_local->base.scheduling_nodes[i] = (scheduling_node_t*)enclave_info;
 
     // Encode the connection topology into the enclave_info object.
-    enclave_info->base.num_downstream = lf_get_downstream_of(i, &enclave_info->base.downstream);
-    enclave_info->base.num_upstream = lf_get_upstream_of(i, &enclave_info->base.upstream);
-    lf_get_upstream_delay_of(i, &enclave_info->base.upstream_delay);
+    enclave_info->base.num_immediate_downstreams = _lf_get_downstream_of(i, &enclave_info->base.immediate_downstreams);
+    enclave_info->base.num_immediate_upstreams = _lf_get_upstream_of(i, &enclave_info->base.immediate_upstreams);
+    _lf_get_upstream_delay_of(i, &enclave_info->base.immediate_upstream_delays);
 
     enclave_info->base.state = GRANTED;
   }
@@ -112,7 +112,7 @@ tag_t rti_next_event_tag_locked(enclave_info_t* e, tag_t next_event_tag) {
   }
 
   // If this enclave has no upstream, then we give a TAG till forever straight away.
-  if (e->base.num_upstream == 0) {
+  if (e->base.num_immediate_upstreams == 0) {
     LF_PRINT_LOG("RTI: enclave %u has no upstream. Giving it a to the NET", e->base.id);
     e->base.last_granted = next_event_tag;
   }
@@ -191,6 +191,10 @@ void notify_provisional_tag_advance_grant(scheduling_node_t* e, tag_t tag) {
   LF_PRINT_LOG("RTI: enclave %u callback with PTAG " PRINTF_TAG " ", e->id, tag.time - lf_time_start(), tag.microstep);
 }
 
+void notify_downstream_next_event_tag(scheduling_node_t* e, tag_t tag) {
+  // Nothing to do here.
+}
+
 void free_scheduling_nodes(scheduling_node_t** scheduling_nodes, uint16_t number_of_scheduling_nodes) {
   // Nothing to do here.
 }

core/federated/RTI/rti_remote.c

@@ -251,8 +251,8 @@ void notify_provisional_tag_advance_grant(scheduling_node_t* e, tag_t tag) {
     // Note that this is transitive.
     // NOTE: This is not needed for enclaves because zero-delay loops are prohibited.
     // It's only needed for federates, which is why this is implemented here.
-    for (int j = 0; j < e->num_upstream; j++) {
-      scheduling_node_t* upstream = rti_remote->base.scheduling_nodes[e->upstream[j]];
+    for (int j = 0; j < e->num_immediate_upstreams; j++) {
+      scheduling_node_t* upstream = rti_remote->base.scheduling_nodes[e->immediate_upstreams[j]];
 
       // Ignore this federate if it has resigned.
       if (upstream->state == NOT_CONNECTED)
@@ -272,6 +272,35 @@ void notify_provisional_tag_advance_grant(scheduling_node_t* e, tag_t tag) {
   }
 }
 
+void notify_downstream_next_event_tag(scheduling_node_t* e, tag_t tag) {
+  if (e->state == NOT_CONNECTED) {
+    return;
+  }
+  // Need to make sure that the destination federate's thread has already
+  // sent the starting MSG_TYPE_TIMESTAMP message.
+  while (e->state == PENDING) {
+    // Need to wait here.
+    lf_cond_wait(&sent_start_time);
+  }
+  size_t message_length = 1 + sizeof(int64_t) + sizeof(uint32_t);
+  unsigned char buffer[message_length];
+  buffer[0] = MSG_TYPE_DOWNSTREAM_NEXT_EVENT_TAG;
+  encode_int64(tag.time, &(buffer[1]));
+  encode_int32((int32_t)tag.microstep, &(buffer[1 + sizeof(int64_t)]));
+
+  if (rti_remote->base.tracing_enabled) {
+    tracepoint_rti_to_federate(send_DNET, e->id, &tag);
+  }
+  if (write_to_socket(((federate_info_t*)e)->socket, message_length, buffer)) {
+    lf_print_error("RTI failed to send downstream next event tag to federate %d.", e->id);
+    e->state = NOT_CONNECTED;
+  } else {
+    e->last_DNET = tag;
+    LF_PRINT_LOG("RTI sent to federate %d the Downstream Next Event Tag (DNET) " PRINTF_TAG ".", e->id,
+                 tag.time - start_time, tag.microstep);
+  }
+}
+
 void update_federate_next_event_tag_locked(uint16_t federate_id, tag_t next_event_tag) {
   federate_info_t* fed = GET_FED_INFO(federate_id);
   tag_t min_in_transit_tag = pqueue_tag_peek_tag(fed->in_transit_message_tags);
@@ -1325,31 +1354,29 @@ static int receive_connection_information(int* socket_id, uint16_t fed_id) {
   } else {
     federate_info_t* fed = GET_FED_INFO(fed_id);
     // Read the number of upstream and downstream connections
-    fed->enclave.num_upstream = extract_int32(&(connection_info_header[1]));
-    fed->enclave.num_downstream = extract_int32(&(connection_info_header[1 + sizeof(int32_t)]));
-    LF_PRINT_DEBUG("RTI got %d upstreams and %d downstreams from federate %d.", fed->enclave.num_upstream,
-                   fed->enclave.num_downstream, fed_id);
+    fed->enclave.num_immediate_upstreams = extract_int32(&(connection_info_header[1]));
+    fed->enclave.num_immediate_downstreams = extract_int32(&(connection_info_header[1 + sizeof(int32_t)]));
+    LF_PRINT_DEBUG("RTI got %d upstreams and %d downstreams from federate %d.", fed->enclave.num_immediate_upstreams,
+                   fed->enclave.num_immediate_downstreams, fed_id);
 
     // Allocate memory for the upstream and downstream pointers
-    if (fed->enclave.num_upstream > 0) {
-      fed->enclave.upstream = (uint16_t*)malloc(sizeof(uint16_t) * fed->enclave.num_upstream);
-      LF_ASSERT_NON_NULL(fed->enclave.upstream);
+    if (fed->enclave.num_immediate_upstreams > 0) {
+      fed->enclave.immediate_upstreams = (uint16_t*)malloc(sizeof(uint16_t) * fed->enclave.num_immediate_upstreams);
       // Allocate memory for the upstream delay pointers
-      fed->enclave.upstream_delay = (interval_t*)malloc(sizeof(interval_t) * fed->enclave.num_upstream);
-      LF_ASSERT_NON_NULL(fed->enclave.upstream_delay);
+      fed->enclave.immediate_upstream_delays =
+          (interval_t*)malloc(sizeof(interval_t) * fed->enclave.num_immediate_upstreams);
     } else {
-      fed->enclave.upstream = (uint16_t*)NULL;
-      fed->enclave.upstream_delay = (interval_t*)NULL;
+      fed->enclave.immediate_upstreams = (uint16_t*)NULL;
+      fed->enclave.immediate_upstream_delays = (interval_t*)NULL;
     }
-    if (fed->enclave.num_downstream > 0) {
-      fed->enclave.downstream = (uint16_t*)malloc(sizeof(uint16_t) * fed->enclave.num_downstream);
-      LF_ASSERT_NON_NULL(fed->enclave.downstream);
+    if (fed->enclave.num_immediate_downstreams > 0) {
+      fed->enclave.immediate_downstreams = (uint16_t*)malloc(sizeof(uint16_t) * fed->enclave.num_immediate_downstreams);
     } else {
-      fed->enclave.downstream = (uint16_t*)NULL;
+      fed->enclave.immediate_downstreams = (uint16_t*)NULL;
     }
 
-    size_t connections_info_body_size = ((sizeof(uint16_t) + sizeof(int64_t)) * fed->enclave.num_upstream) +
-                                        (sizeof(uint16_t) * fed->enclave.num_downstream);
+    size_t connections_info_body_size = ((sizeof(uint16_t) + sizeof(int64_t)) * fed->enclave.num_immediate_upstreams) +
+                                        (sizeof(uint16_t) * fed->enclave.num_immediate_downstreams);
     unsigned char* connections_info_body = NULL;
     if (connections_info_body_size > 0) {
       connections_info_body = (unsigned char*)malloc(connections_info_body_size);
@@ -1360,16 +1387,16 @@ static int receive_connection_information(int* socket_id, uint16_t fed_id) {
       // Keep track of where we are in the buffer
       size_t message_head = 0;
       // First, read the info about upstream federates
-      for (int i = 0; i < fed->enclave.num_upstream; i++) {
-        fed->enclave.upstream[i] = extract_uint16(&(connections_info_body[message_head]));
+      for (int i = 0; i < fed->enclave.num_immediate_upstreams; i++) {
+        fed->enclave.immediate_upstreams[i] = extract_uint16(&(connections_info_body[message_head]));
         message_head += sizeof(uint16_t);
-        fed->enclave.upstream_delay[i] = extract_int64(&(connections_info_body[message_head]));
+        fed->enclave.immediate_upstream_delays[i] = extract_int64(&(connections_info_body[message_head]));
         message_head += sizeof(int64_t);
       }
 
       // Next, read the info about downstream federates
-      for (int i = 0; i < fed->enclave.num_downstream; i++) {
-        fed->enclave.downstream[i] = extract_uint16(&(connections_info_body[message_head]));
+      for (int i = 0; i < fed->enclave.num_immediate_downstreams; i++) {
+        fed->enclave.immediate_downstreams[i] = extract_uint16(&(connections_info_body[message_head]));
         message_head += sizeof(uint16_t);
       }
 
@@ -1738,6 +1765,7 @@ void initialize_RTI(rti_remote_t* rti) {
   rti_remote->clock_sync_exchanges_per_interval = 10;
   rti_remote->authentication_enabled = false;
   rti_remote->base.tracing_enabled = false;
+  rti_remote->base.dnet_disabled = false;
   rti_remote->stop_in_progress = false;
 }
 
@@ -1748,17 +1776,15 @@ void clock_sync_add_offset(instant_t* t) { (void)t; }
 void clock_sync_subtract_offset(instant_t* t) { (void)t; }
 
 void free_scheduling_nodes(scheduling_node_t** scheduling_nodes, uint16_t number_of_scheduling_nodes) {
+  invalidate_min_delays();
   for (uint16_t i = 0; i < number_of_scheduling_nodes; i++) {
     scheduling_node_t* node = scheduling_nodes[i];
-    if (node->upstream != NULL) {
-      free(node->upstream);
-      free(node->upstream_delay);
-    }
-    if (node->min_delays != NULL) {
-      free(node->min_delays);
+    if (node->immediate_upstreams != NULL) {
+      free(node->immediate_upstreams);
+      free(node->immediate_upstream_delays);
     }
-    if (node->downstream != NULL) {
-      free(node->downstream);
+    if (node->immediate_downstreams != NULL) {
+      free(node->immediate_downstreams);
     }
     free(node);
   }

core/federated/RTI/rti_remote.h

@@ -154,6 +154,7 @@ typedef struct rti_remote_t {
    * Boolean indicating that authentication is enabled.
    */
   bool authentication_enabled;
+
   /**
    * Boolean indicating that a stop request is already in progress.
    */