Don't allow two beanstalkds to run in one dir.

beanstalkd.c

@@ -253,6 +253,13 @@ main(int argc, char **argv)
     job_init();
     prot_init();
 
+    /* We want to make sure that only one beanstalkd tries to use the binlog
+     * directory at a time. So acquire a lock now and never release it. */
+    if (binlog_dir) {
+        r = binlog_lock();
+        if (!r) twarnx("failed to lock binlog dir %s", binlog_dir), exit(10);
+    }
+
     r = make_server_socket(host_addr, port);
     if (r == -1) twarnx("make_server_socket()"), exit(111);
 

binlog.c

@@ -42,6 +42,7 @@ static int binlog_index = 0;
 static int binlog_fd = -1;
 static int binlog_version = 1;
 static size_t bytes_written;
+static int lock_fd;
 
 static binlog first_binlog = NULL, last_binlog = NULL;
 
@@ -356,6 +357,29 @@ binlog_read(job binlog_jobs)
     }
 }
 
+int
+binlog_lock()
+{
+    int r;
+    struct flock lock;
+    char path[PATH_MAX];
+
+    r = snprintf(path, PATH_MAX, "%s/lock", binlog_dir);
+    if (r > PATH_MAX) return twarnx("path too long: %s", binlog_dir), 0;
+
+    lock_fd = open(path, O_WRONLY|O_CREAT, 0600);
+    if (lock_fd == -1) return twarn("open"), 0;
+
+    lock.l_type = F_WRLCK;
+    lock.l_whence = SEEK_SET;
+    lock.l_start = 0;
+    lock.l_len = 0;
+    r = fcntl(lock_fd, F_SETLK, &lock);
+    if (r) return twarn("fcntl"), 0;
+
+    return 1;
+}
+
 void
 binlog_init()
 {

binlog.h

@@ -32,6 +32,9 @@ struct binlog {
 extern char *binlog_dir;
 extern size_t binlog_size_limit;
 
+/* Return the number of locks acquired: either 0 or 1. */
+int binlog_lock();
+
 void binlog_write_job(job j);
 void binlog_read(job binlog_jobs);
 void binlog_close();