Kill daemon at end of queue

main.c

@@ -5,6 +5,7 @@
 #include <sys/un.h>
 #include <sys/wait.h>
 #include <sys/prctl.h>
+#include <fcntl.h>
 #include "util.h"
 #include "postprocess.h"
 
@@ -31,7 +32,8 @@ is_daemon_running()
 	struct timeval tv;
 
 	// Daemon isn't running if the socket doesn't exist
-	if (!access(socket_path, F_OK)) {
+	if (access(socket_path, F_OK)) {
+		fprintf(stderr, "[fg] daemon socket doesn't exist\n");
 		return 0;
 	}
 
@@ -51,6 +53,7 @@ is_daemon_running()
 	addr.sun_family = AF_UNIX;
 	strncpy(addr.sun_path, socket_path, sizeof(addr.sun_path) - 1);
 	if (connect(sock, (struct sockaddr *) &addr, sizeof(struct sockaddr_un)) < 0) {
+		err("[fg] could not open daemon socket");
 		return 0;
 	}
 
@@ -140,6 +143,7 @@ start_background_process()
 	unsigned int cli_len;
 	struct Job job;
 	char buffer[272];
+	int first = 1;
 
 	const char *name_fg = "postprocessd fg";
 	const char *name_bg = "postprocessd bg";
@@ -197,12 +201,29 @@ start_background_process()
 	sock = listen_on_socket();
 	fprintf(stderr, "[bg] socket created\n");
 
+	fprintf(stderr, "[bg] first accept start\n");
 	while (1) {
 		fd = accept(sock, (struct sockaddr *) &cli_addr, &cli_len);
-		if (fd < 0) {
+
+		if (fd < 0 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
+			if (first) {
+				// When no queued item has been processed yet act like a proper nonblocking accept
+				// Doing a busy loop isn't very efficient but this should last for less than a second
+				usleep(100);
+				continue;
+			}
+
+			// No client was available after processing the first image. Kill the background process
+			fprintf(stderr, "[bg] shutting down\n");
+			close(sock);
+			unlink(socket_path);
+			exit(0);
+		} else if (fd < 0) {
+			// Something went wrong with the listening socket and it wasn't the nonblocking errnos
 			err("[bg] failed to accept");
 			return 0;
 		}
+
 		fprintf(stderr, "[bg] accepted connection\n");
 		if (read(fd, &job, sizeof(job)) < 0) {
 			err("[bg] failed to read");
@@ -210,6 +231,7 @@ start_background_process()
 		}
 		fprintf(stderr, "[bg] start processing job\n");
 		start_processing(job);
+		first = 0;
 		wait(NULL);
 		fprintf(stderr, "[bg] job done\n");
 
@@ -219,6 +241,9 @@ start_background_process()
 			err("[bg] failed to write response");
 		}
 		close(fd);
+
+		// Make the listen socket nonblocking
+		fcntl(sock, F_SETFL, O_NONBLOCK);
 	}
 }