option to check if modbus client is still alive

Author: NikolasK-source

src/main.cpp

@@ -115,6 +115,11 @@ int main(int argc, char **argv) {
     options.add_options("shared memory")("semaphore-timeout",
                                          "maximum time (in seconds) to wait for semaphore (default: 0.1)",
                                          cxxopts::value<double>()->default_value("0.1"));
+    options.add_options("shared_memory")(
+            "pid",
+            "terminate application if application with given pid is terminated. Provide "
+            "the pid of the modbus client to terminate when the mosbus client is terminated.",
+            cxxopts::value<pid_t>());
 
     // parse arguments
     cxxopts::ParseResult args;
@@ -425,6 +430,11 @@ int main(int argc, char **argv) {
             std::cerr << e.what() << '\n';
             return EX_SOFTWARE;
         }
+    } else {
+        std::cerr << "WARNING: No semaphore specified.\n"
+                     "         Concurrent access to the shared memory is possible that can result in CORRUPTED DATA.\n"
+                     "         Use --semaphore to specify a semaphore that is provided by the Modbus client.\n";
+        std::cerr << std::flush;
     }
 
     const double SEMAPHORE_TIMEOUT_S = args["semaphore-timeout"].as<double>();
@@ -439,6 +449,22 @@ int main(int argc, char **argv) {
             static_cast<suseconds_t>(std::modf(SEMAPHORE_TIMEOUT_S, &modf_dummy) * 1'000'000),
     };
 
+    // modbus client pid
+    pid_t mb_client_pid     = 0;
+    bool  use_mb_client_pid = false;
+    if (args.count("pid")) {
+        mb_client_pid     = args["pid"].as<pid_t>();
+        use_mb_client_pid = true;
+    } else {
+        std::cerr << "WARNING: No Modbus client pid provided.\n"
+                     "         Terminating the Modbus client application WILL NOT result in the termination of this "
+                     "application.\n"
+                     "         This application WILL NOT connect to the shared memory of a restarted Modbus client.\n"
+                     "         Use --pid to specify the pid of the modbus client.\n"
+                     "         Command line example: --pid $(pidof modbus-tcp-client-shm)\n"
+                  << std::flush;
+    }
+
     std::cout << std::fixed;
 
     auto last_time  = std::chrono::steady_clock::now();
@@ -648,6 +674,20 @@ int main(int argc, char **argv) {
     input_thread.detach();
 
     while (!terminate) {
+        if (use_mb_client_pid) {
+            // check if modbus client is still alive
+            int tmp = kill(mb_client_pid, 0);
+            if (tmp == -1) {
+                if (errno == ESRCH) {
+                    std::cerr << "Modbus client (pid=" << mb_client_pid << ") no longer alive.\n" << std::flush;
+                } else {
+                    perror("failed to send signal to modbus client");
+                }
+                terminate = true;
+                break;
+            }
+        }
+
         std::this_thread::sleep_for(std::chrono::milliseconds(100));  // NOLINT
     }