Fix segfault on closing down network connections

core/federated/federate.c

@@ -641,11 +641,16 @@ static int handle_tagged_message(net_abstraction_t net, int fed_id) {
                      "    Discarding message and closing the network connection.",
                      env->current_tag.time - start_time, env->current_tag.microstep, intended_tag.time - start_time,
                      intended_tag.microstep);
-      // Free the allocated memory before returning
-      _lf_done_using(message_token);
-      // Close network abstraction, reading any incoming data and discarding it.
-      shutdown_net(_fed.net_for_inbound_p2p_connections[fed_id], false);
-      _fed.net_for_inbound_p2p_connections[fed_id] = NULL;
+      // The token was freshly allocated by _lf_new_token with ref_count 0 and was never
+      // scheduled, so _lf_done_using would incorrectly treat it as already freed.
+      // Use _lf_free_token directly, which handles ref_count == 0 correctly.
+      _lf_free_token(message_token);
+#ifdef FEDERATED_DECENTRALIZED
+      _lf_decrement_tag_barrier_locked(env);
+#endif
+      // Close the connection to unblock the listener, but do not free the memory;
+      // lf_terminate_execution will free it after joining the listener thread.
+      close_net(net, false);
       LF_MUTEX_UNLOCK(&env->mutex);
       return -1;
     } else {
@@ -1508,23 +1513,21 @@ static void* listen_to_rti_net(void* args) {
   // Listen for messages from the federate.
   while (!_lf_termination_executed) {
     // Check whether the RTI network abstraction is still valid.
-    if (_fed.net_to_RTI == NULL) {
-      lf_print_warning("network abstraction to the RTI unexpectedly closed.");
+    if (_fed.net_to_RTI == NULL || !is_net_open(_fed.net_to_RTI)) {
+      lf_print_warning("network connection to the RTI unexpectedly closed.");
       return NULL;
     }
     // Read one byte to get the message type.
     // This will exit if the read fails.
     int read_failed = read_from_net(_fed.net_to_RTI, 1, buffer);
     if (read_failed < 0) {
       lf_print_error("Connection to the RTI was closed by the RTI with an error. Considering this a soft error.");
-      shutdown_net(_fed.net_to_RTI, false);
-      _fed.net_to_RTI = NULL;
+      close_net(_fed.net_to_RTI, false);
       return NULL;
     } else if (read_failed > 0) {
       // EOF received.
       lf_print_info("Connection to the RTI closed with an EOF.");
-      shutdown_net(_fed.net_to_RTI, false);
-      _fed.net_to_RTI = NULL;
+      close_net(_fed.net_to_RTI, false);
       return NULL;
     }
     switch (buffer[0]) {
@@ -1647,22 +1650,17 @@ void lf_terminate_execution(environment_t* env) {
   }
 
   LF_PRINT_DEBUG("Closing incoming P2P network abstractions.");
-  // Close any incoming P2P network abstractions that are still open.
+  // Close connections to unblock any listener threads that are blocking on reads,
+  // but do NOT free the memory yet because listener threads hold local pointers.
   for (int i = 0; i < NUMBER_OF_FEDERATES; i++) {
-    shutdown_net(_fed.net_for_inbound_p2p_connections[i], false);
-    // Ignore errors. Mark the network abstraction closed.
-    _fed.net_for_inbound_p2p_connections[i] = NULL;
+    close_net(_fed.net_for_inbound_p2p_connections[i], false);
   }
 
   // Check for all outgoing physical connections in
   // _fed.net_for_outbound_p2p_connections and
   // if the network abstraction ID is not NULL, the connection is still open.
   // Send an EOF by closing the network abstraction here.
   for (int i = 0; i < NUMBER_OF_FEDERATES; i++) {
-
-    // Close outbound connections, in case they have not closed themselves.
-    // This will result in EOF being sent to the remote federate, except for
-    // abnormal termination, in which case it will just close the network abstraction.
     close_outbound_net(i);
   }
 
@@ -1681,6 +1679,14 @@ void lf_terminate_execution(environment_t* env) {
   // Wait for the thread listening for messages from the RTI to close.
   lf_thread_join(_fed.RTI_net_listener, NULL);
 
+  // All listener threads have now exited. Safe to free network abstraction memory.
+  for (int i = 0; i < NUMBER_OF_FEDERATES; i++) {
+    free_net(_fed.net_for_inbound_p2p_connections[i]);
+    _fed.net_for_inbound_p2p_connections[i] = NULL;
+  }
+  free_net(_fed.net_to_RTI);
+  _fed.net_to_RTI = NULL;
+
   // For abnormal termination, there is no need to free memory.
   if (_lf_normal_termination) {
     LF_PRINT_DEBUG("Freeing memory occupied by the federate.");

network/api/net_abstraction.h

@@ -204,13 +204,44 @@ void write_to_net_fail_on_error(net_abstraction_t net_abs, size_t num_bytes, uns
 bool is_net_open(net_abstraction_t net_abs);
 
 /**
- * @brief Gracefully shut down and close a network abstraction.
+ * @brief Close the underlying connection of a network abstraction without freeing its memory.
  * @ingroup Network
  *
+ * This function closes the connection (making it unusable for I/O) but leaves the
+ * net_abstraction_t memory allocated. This is needed when another thread may still hold
+ * a pointer to the same network abstraction; the socket is closed to unblock any pending
+ * reads, but the memory remains valid. Call free_net() to release the memory after ensuring
+ * no other thread holds a reference. This function is idempotent.
+ *
+ * @param net_abs The network abstraction whose connection should be closed, or NULL (no-op).
+ * @param read_before_closing If true, read until EOF before closing.
+ * @return int Returns 0 on success, -1 on failure.
+ */
+int close_net(net_abstraction_t net_abs, bool read_before_closing);
+
+/**
+ * @brief Free the memory associated with a network abstraction.
+ * @ingroup Network
+ *
+ * The connection should already have been closed via close_net() or shutdown_net().
+ * Safe to call with NULL (no-op).
+ *
+ * @param net_abs The network abstraction to free, or NULL.
+ */
+void free_net(net_abstraction_t net_abs);
+
+/**
+ * @brief Gracefully shut down, close, and free a network abstraction.
+ * @ingroup Network
+ *
+ * Equivalent to calling close_net() followed by free_net(). Do not use this function
+ * if another thread may still be using the same net_abstraction_t pointer; use close_net()
+ * to unblock the other thread first, join it, and then call free_net().
+ *
  * If read_before_closing is false, call shutdown() with SHUT_RDWR and then close(). If true, call shutdown() with
  * SHUT_WR, then read() until EOF and discard received bytes before closing.
  *
- * @param net_abs The network abstraction to shut down and close.
+ * @param net_abs The network abstraction to shut down and close, or NULL (no-op).
  * @param read_before_closing If true, read until EOF before closing the network abstraction.
  * @return int Returns 0 on success, -1 on failure (errno will indicate the error).
  */

network/impl/src/lf_socket_support.c

@@ -176,13 +176,16 @@ bool is_net_open(net_abstraction_t net_abs) {
   return is_socket_open(priv->socket_descriptor);
 }
 
-int shutdown_net(net_abstraction_t net_abs, bool read_before_closing) {
+int close_net(net_abstraction_t net_abs, bool read_before_closing) {
   if (net_abs == NULL) {
-    LF_PRINT_LOG("Socket already closed.");
     return 0;
   }
   socket_priv_t* priv = (socket_priv_t*)net_abs;
-  int ret = shutdown_socket(&priv->socket_descriptor, read_before_closing);
+  return shutdown_socket(&priv->socket_descriptor, read_before_closing);
+}
+
+int shutdown_net(net_abstraction_t net_abs, bool read_before_closing) {
+  int ret = close_net(net_abs, read_before_closing);
   free_net(net_abs);
   return ret;
 }

util/initialize_from_file.h

@@ -47,7 +47,7 @@ extern "C" {
  *
  * To use this to initialize parameters and/or state variables of a reactor, you can do the following:
  *
- * ```lf-c
+ * ```lf
  * main reactor MyReactor(x: double = 0.0, row_number: int = 0) {
  *   state y: double = 0.0;
  *   reaction(startup) {=
@@ -67,7 +67,7 @@ extern "C" {
  * If you wish to initialize parameters or state variables of a reactor within a bank, you
  * can create a CSV file with one row per bank member and use the `bank_index` parameter to
  * select the row to read. For example:
- * ```lf-c
+ * ```lf
  * reactor MyReactor(bank_index: int = 0) {
  *   reaction(startup) {=
  *     lf_initialize_double("params.csv", ',', self->bank_index + 1, &self->x, &self->y, NULL);
@@ -79,7 +79,7 @@ extern "C" {
  * This way, each bank member can have a different set of parameter values.
  *
  * To use this in a Lingua Franca program, you must include the following in the target declaration:
- * ```lf-c
+ * ```lf
  * target C {
  *  cmake-include: "/lib/c/reactor-c/util/initialize_from_file.cmake",
  *  files: [
@@ -89,7 +89,7 @@ extern "C" {
  * ```
  *
  * Then, in the reactor, you can include the header file as follows:
- * ```lf-c
+ * ```lf
  * reactor MyReactor {
  *   preamble {=
  *     #include "initialize_from_file.h"
@@ -134,7 +134,7 @@ int lf_initialize_double(const char* filename, char delimiter, size_t row_number
  *
  * To use this to initialize parameters and/or state variables of a reactor, you can do the following:
  *
- * ```lf-c
+ * ```lf
  * main reactor MyReactor(x: int = 0, row_number: int = 0) {
  *   state y: int = 0;
  *   reaction(startup) {=
@@ -154,7 +154,7 @@ int lf_initialize_double(const char* filename, char delimiter, size_t row_number
  * If you wish to initialize parameters or state variables of a reactor within a bank, you
  * can create a CSV file with one row per bank member and use the `bank_index` parameter to
  * select the row to read. For example:
- * ```lf-c
+ * ```lf
  * reactor MyReactor(bank_index: int = 0) {
  *   reaction(startup) {=
  *     lf_initialize_int("params.csv", ',', self->bank_index + 1, &self->x, &self->y, NULL);
@@ -166,7 +166,7 @@ int lf_initialize_double(const char* filename, char delimiter, size_t row_number
  * This way, each bank member can have a different set of parameter values.
  *
  * To use this in a Lingua Franca program, you must include the following in the target declaration:
- * ```lf-c
+ * ```lf
  * target C {
  *  cmake-include: "/lib/c/reactor-c/util/initialize_from_file.cmake",
  *  files: [
@@ -176,7 +176,7 @@ int lf_initialize_double(const char* filename, char delimiter, size_t row_number
  * ```
  *
  * Then, in the reactor, you can include the header file as follows:
- * ```lf-c
+ * ```lf
  * reactor MyReactor {
  *   preamble {=
  *     #include "initialize_from_file.h"
@@ -206,7 +206,7 @@ int lf_initialize_int(const char* filename, char delimiter, size_t row_number, .
  *
  * This macro is meant to be called from a reaction, not directly. If you wish to call it from
  * somewhere other than a reaction, you can use the following function:
- * ```lf-c
+ * ```lf
  * int _lf_initialize_string(const char* filename, char delimiter, size_t row_number,
  *                          struct allocation_record_t** allocations, ...);
  * ```
@@ -238,7 +238,7 @@ int lf_initialize_int(const char* filename, char delimiter, size_t row_number, .
  *
  * To use this to initialize parameters and/or state variables of a reactor, you can do the following:
  *
- * ```lf-c
+ * ```lf
  * main reactor MyReactor(row_number: int = 0) {
  *   state name: string = "";
  *   reaction(startup) {=
@@ -258,7 +258,7 @@ int lf_initialize_int(const char* filename, char delimiter, size_t row_number, .
  * If you wish to initialize parameters or state variables of a reactor within a bank, you
  * can create a CSV file with one row per bank member and use the `bank_index` parameter to
  * select the row to read. For example:
- * ```lf-c
+ * ```lf
  * reactor MyReactor(bank_index: int = 0) {
  *   reaction(startup) {=
  *     lf_initialize_string("params.csv", ',', self->bank_index + 1, &self->name, NULL);
@@ -270,7 +270,7 @@ int lf_initialize_int(const char* filename, char delimiter, size_t row_number, .
  * This way, each bank member can have a different set of parameter values.
  *
  * To use this in a Lingua Franca program, you must include the following in the target declaration:
- * ```lf-c
+ * ```lf
  * target C {
  *  cmake-include: "/lib/c/reactor-c/util/initialize_from_file.cmake",
  *  files: [
@@ -280,7 +280,7 @@ int lf_initialize_int(const char* filename, char delimiter, size_t row_number, .
  * ```
  *
  * Then, in the reactor, you can include the header file as follows:
- * ```lf-c
+ * ```lf
  * reactor MyReactor {
  *   preamble {=
  *     #include "initialize_from_file.h"