If a signal handler runs during select() loop in clixon_event_loop() and unless the signal handler sets clixon_exit, the select will be restarted.

CHANGELOG.md

@@ -112,6 +112,9 @@ Developers may need to change their code
 
 ### Minor changes
 
+* If a signal handler runs during `select()` loop in `clixon_event_loop()` and unless the signal handler sets clixon_exit, the select will be restarted.
+  * Existing behavior for SIGTERM/SIGINT to exit is maintained
+  * This was for supporting SIGCHLD of forked restconf that crashes or being killed externally.
 * Look for symbols in plugins using `dlsym(RTLD_DEFAULT)` instead of `dlsym(NULL)` for more portable use
   * Thanks jdl@netgate.com
 * Added support for the following XPATH functions:

apps/backend/backend_main.c

@@ -48,6 +48,7 @@
 #include <signal.h>
 #include <fcntl.h>
 #include <time.h>
+#include <wait.h>
 #include <syslog.h>
 #include <ifaddrs.h>
 #include <sys/time.h>
@@ -158,6 +159,21 @@ backend_sig_term(int arg)
     clicon_exit_set(); /* checked in clixon_event_loop() */
 }
 
+/*! wait for killed child
+ * primary use in case restconf daemon forked using process-control API
+ * This may cause EINTR in eg select() in clixon_event_loop() which will be ignored
+ */
+static void
+backend_sig_child(int arg)
+{
+    int status;
+    int pid;
+
+    clicon_debug(1, "%s", __FUNCTION__);
+    if ((pid = waitpid(-1, &status, 0)) != -1 && WIFEXITED(status)){
+    }
+}
+
 /*! Create backend server socket and register callback
  * @param[in]  h    Clicon handle
  * @retval     s    Server socket file descriptor (see socket(2))
@@ -996,7 +1012,11 @@ main(int    argc,
 	clicon_err(OE_DAEMON, errno, "Setting signal");
 	goto done;
     }
-
+    /* This is in case restconf daemon forked using process-control API */
+    if (set_signal(SIGCHLD, backend_sig_child, NULL) < 0){
+	clicon_err(OE_DAEMON, errno, "Setting signal");
+	goto done;
+    }
     /* Initialize server socket and save it to handle */
     if ((ss = backend_server_socket(h)) < 0)
 	goto done;

lib/src/clixon_event.c

@@ -55,6 +55,7 @@
 #include "clixon_queue.h"
 #include "clixon_log.h"
 #include "clixon_err.h"
+#include "clixon_sig.h"
 #include "clixon_event.h"
 
 /*
@@ -199,7 +200,7 @@ clixon_event_unreg_fd(int   s,
  * Note also that the callback is not periodic, you need to make a new 
  * registration for each period, see example above.
  * Note also that the first argument to fn is a dummy, just to get the same
- * signatute as for file-descriptor callbacks.
+ * signature as for file-descriptor callbacks.
  * @see clixon_event_reg_fd
  * @see clixon_event_unreg_timeout
  */
@@ -319,10 +320,18 @@ clixon_event_loop(void)
 	if (clicon_exit_get())
 	    break;
 	if (n == -1) {
+	    /* Signals either set clixon_exit, then the function returns 0
+	     * Typically for set_signal() of SIGTERM,SIGINT, etc
+	     * Other signals are ignored, and the select is rerun, eg SIGCHLD
+	     */
 	    if (errno == EINTR){
 		clicon_debug(1, "%s select: %s", __FUNCTION__, strerror(errno));
-		clicon_err(OE_EVENTS, errno, "select");
-		retval = 0;
+		if (clicon_exit_get()){
+		    clicon_err(OE_EVENTS, errno, "select");
+		    retval = 0;
+		}
+		else
+		    continue;
 	    }
 	    else
 		clicon_err(OE_EVENTS, errno, "select");

lib/src/clixon_sig.c

@@ -68,7 +68,7 @@ set_signal(int     signo,
 
     snew.sa_handler = handler;
     sigemptyset(&snew.sa_mask);
-     snew.sa_flags = 0;
+     snew.sa_flags = SA_RESTART;
      if (sigaction(signo, &snew, &sold) < 0){
 	clicon_err(OE_UNIX, errno, "sigaction");
 	return -1;

test/test_restconf_rpc.sh

@@ -136,6 +136,9 @@ if [ -z "$ps" ]; then
     err "A restconf running"
 fi
 
+new "try restconf rpc"
+expectpart "$(curl $CURLOPTS -X POST -H "Content-Type: application/yang-data+json" $RCPROTO://localhost/restconf/operations/clixon-lib:process-control -d '{"clixon-lib:input":{"name":"restconf","operation":"status"}}')" 0 "HTTP/1.1 200 OK" '{"clixon-lib:output":{"pid":'
+
 new "stop restconf RPC"
 pid=$(testrpc stop 0)
 if [ $? -ne 0 ]; then echo "$pid";exit -1; fi