Use return value of fd-mux Loop().

Make the return value of Loop() more meaningfuil (a boolean
returning tru if everything was fine - opposite to the integer
returned before). Use that in machine-control (previously, machine
control was actually not (anymore?) looking at that result. The
'ret' value was only initialized, never set.

Rename the static volatile signal state variables in fd-mux to have
prefix `s_` for improved readability.

Author: hzeller

src/common/fd-mux.cc

@@ -31,24 +31,24 @@
 #include "common/logging.h"
 
 // A signal that should trigger exiting the loop
-static volatile sig_atomic_t caught_exit_trigger_signal = 0;
+static volatile sig_atomic_t s_caught_exit_trigger_signal = 0;
 
 // A signal that is harmless for our context and shall be ignored.
-static volatile sig_atomic_t caught_ignored_signal = 0;
+static volatile sig_atomic_t s_caught_ignored_signal = 0;
 
 static void receive_signal(int signo) {
   static const char msg[] = "Caught signal. Shutting down ASAP.\n";
-  if (!caught_exit_trigger_signal) {  // only print message once.
+  if (!s_caught_exit_trigger_signal) {  // only print message once.
     write(STDERR_FILENO, msg, sizeof(msg));
   }
-  caught_exit_trigger_signal = 1;
+  s_caught_exit_trigger_signal = 1;
 }
 
-static void ignore_signal(int signo) { caught_ignored_signal = 1; }
+static void ignore_signal(int signo) { s_caught_ignored_signal = 1; }
 
 static void arm_signal_handler() {
-  caught_exit_trigger_signal = 0;
-  caught_ignored_signal = 0;
+  s_caught_exit_trigger_signal = 0;
+  s_caught_ignored_signal = 0;
 
   struct sigaction sa = {};
   sa.sa_handler = receive_signal;
@@ -136,7 +136,7 @@ bool FDMultiplexer::SingleCycle(unsigned int timeout_ms) {
 
   int fds_ready = select(maxfd + 1, &read_fds, &write_fds, nullptr, &timeout);
   if (fds_ready < 0) {
-    if (!caught_exit_trigger_signal) perror("select() failed");
+    if (!s_caught_exit_trigger_signal) perror("select() failed");
     return false;
   }
 
@@ -154,17 +154,17 @@ bool FDMultiplexer::SingleCycle(unsigned int timeout_ms) {
   return true;
 }
 
-int FDMultiplexer::Loop() {
+bool FDMultiplexer::Loop() {
   const unsigned timeout = idle_ms_;
 
   arm_signal_handler();
-  while (SingleCycle(timeout) && !caught_exit_trigger_signal) {
-    if (caught_ignored_signal) {
+  while (SingleCycle(timeout) && !s_caught_exit_trigger_signal) {
+    if (s_caught_ignored_signal) {
       Log_info("Caught SIGPIPE. Ignored.\n");
-      caught_ignored_signal = 0;
+      s_caught_ignored_signal = 0;
     }
   }
   disarm_signal_handler();
 
-  return caught_exit_trigger_signal ? 1 : 0;
+  return !s_caught_exit_trigger_signal;
 }

src/common/fd-mux.h

@@ -46,8 +46,9 @@ class FDMultiplexer {
   void RunOnIdle(const Handler &handler);
 
   // Run the main loop. Blocks while there is still a filedescriptor
-  // registered (return 0) or until a signal is triggered (return 1).
-  int Loop();
+  // registered.
+  // Return `true` on sucess, `false` if we exited due to some signal.
+  bool Loop();
 
  protected:
   // Run a single cycle resulting in exactly one call of a handler function.

src/machine-control.cc

@@ -31,6 +31,7 @@
 #include <unistd.h>
 
 #include <cmath>
+#include <cstdlib>
 #include <memory>
 #include <string>
 #include <string_view>
@@ -613,7 +614,6 @@ int main(int argc, char *argv[]) {
     new GCodeParser(parser_cfg, machine_control->ParseEventReceiver());
   GCodeStreamer *const streamer = new GCodeStreamer(
     &event_server, parser, machine_control->ParseEventReceiver());
-  int ret = 0;
   if (has_filename) {
     const char *filename = argv[optind];
     send_file_to_machine(machine_control, streamer, filename);
@@ -627,20 +627,20 @@ int main(int argc, char *argv[]) {
                       machine_control);
   }
 
-  event_server.Loop();  // Run service until Ctrl-C or all sockets closed.
+  // Run service until Ctrl-C or all sockets closed.
+  const bool clean_exit = event_server.Loop();
   Log_info("Exiting.");
 
   delete streamer;
   delete parser;
   delete machine_control;
 
-  const bool caught_signal = (ret == 1);  // ?
-  if (caught_signal) {
+  if (!clean_exit) {
     Log_info(
       "Caught signal: immediate exit. "
       "Skipping potential remaining queue.");
   }
-  motion_backend->Shutdown(!caught_signal);
+  motion_backend->Shutdown(clean_exit);
 
   delete motion_backend;
   delete pru_hw_interface;
@@ -650,5 +650,5 @@ int main(int argc, char *argv[]) {
   parser_cfg.SaveParams();
 
   Log_info("Shutdown.");
-  return ret;
+  return clean_exit ? EXIT_SUCCESS : EXIT_FAILURE;
 }