Do some locking on startup, signal existing supervisors.

1 files changed, 101 insertions, 1 deletions

diff --git a/scan.c b/scan.c
index f9a6b05..ee3b118 100644
--- a/scan.c
+++ b/scan.c
@@ -9,12 +9,18 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/event.h>
+#include <sys/file.h>
 #include <sys/procctl.h>
 #include <sys/queue.h>
 #include <sys/time.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
+/*
+ * TODO:
+ * - Don't start procs instantly after they die, wait some seconds first.
+ */
+
 const char supdir[] = "/home/marius/r/svc";
 char *super_path[] = { "/home/marius/r/supervise", NULL, NULL };
 
@@ -279,12 +285,104 @@ try_wait()
 }
 
 int
+acquire_lock()
+{
+	int lock_fd;
+	char *lock_path;
+
+	if (asprintf(&lock_path, "%s/lock", supdir) == -1 || lock_path == NULL)
+		err(1, "asprintf()");
+
+	if ((lock_fd = open(lock_path, O_CREAT | O_TRUNC | O_WRONLY | O_CLOEXEC, 0644)) == -1)
+		err(1, "open()");
+
+	if (flock(lock_fd, LOCK_EX | LOCK_NB) == -1) {
+		if (errno == EWOULDBLOCK) {
+			fprintf(stderr, "%s is locked\n", lock_path);
+			exit(1);
+		} else {
+			err(1, "flock()");
+		}
+	}
+
+	free(lock_path);
+
+	return lock_fd;
+}
+
+void
+signal_existing(int dir_fd)
+{
+	DIR *dir;
+	struct dirent *dp;
+	char *ctrl_path, *lock_path;
+	int ctrl_fd, lock_fd;
+	sigmask_t mask;
+
+	sigemptyset(&mask);
+	sigaddset(&mask, SIGPIPE);
+
+	dir = fdopendir(dir_fd);
+
+	while ((dp = readdir(dir)) != NULL) {
+		if (dp->d_type != DT_DIR)
+			continue;
+		if (dp->d_name[0] == '.')
+			continue;
+
+		if (asprintf(&ctrl_path, "%s/supervise/control", dp->d_name) == -1 || ctrl_path == NULL)
+			err(1, "asprintf()");
+		if (asprintf(&lock_path, "%s/supervise/lock", dp->d_name) == -1 || lock_path == NULL)
+			err(1, "asprintf()");
+
+		if ((lock_fd = open(lock_path, O_RDONLY | O_NONBLOCK | O_CLOEXEC)) == -1)
+			err(1, "open()");
+
+		if (flock(lock_fd, LOCK_EX | LOCK_NB) == -1) {
+			if (errno == EWOULDBLOCK) {
+				if ((ctrl_fd = open(ctrl_path, O_WRONLY | O_CLOEXEC)) == -1)
+					err(1, "open()");
+
+				if (setprocmask(SIG_BLOCK, &mask, NULL) == -1)
+					err(1, "setprocmask()");
+
+				if (write(ctrl_fd, "x", 1) != 1) {
+					if (errno != EPIPE)
+						err(1, "write()");
+				}
+
+				if (setprocmask(SIG_UNBLOCK, &mask, NULL) == -1)
+					err(1, "setprocmask()");
+
+				if (close(ctrl_fd) == -1)
+					err(1, "close()");
+			} else {
+				err(1, "flock()");
+			}
+		}
+
+		if (close(lock_fd) == -1)
+			err(1, "flock()");
+
+		free(lock_path);
+		free(ctrl_path);
+	}
+
+	rewinddir(dir);
+
+	if (fdclosedir(dir) == -1)
+		err(1, "fdclosedir()");
+}
+
+int
 main(int argc, char **argv)
 {
-	int kq, dir_fd;
+	int kq, dir_fd, lock_fd;
 	struct kevent evt;
 	pid_t mypid = getpid();
 
+	lock_fd = acquire_lock();
+
 	if (procctl(P_PID, mypid, PROC_REAP_ACQUIRE, NULL) == -1)
 		err(1, "procctl()");
 
@@ -323,6 +421,8 @@ main(int argc, char **argv)
 		perror("close()");
 	if (close(dir_fd) == -1)
 		perror("close()");
+	if (close(lock_fd) == -1)
+		perror("close()");
 
 	reset_signals(); /* Make SIGTERM/INT work again in case reap_all uses a long time. */