[#3506] Final improvements

changelog_unreleased/3506-unix-control-socket

@@ -0,0 +1,3 @@
+[func]		fdupont
+	Reorganized UNIX control socket code.
+	(Gitlab #3506)

src/lib/config/unix_command_mgr.cc

@@ -573,19 +573,20 @@ UnixCommandMgrImpl::openCommandSocket(const isc::data::ConstElementPtr& socket_i
 
     // First let's open lock file.
     std::string lock_name = getLockName();
-    int new_lock_fd = open(lock_name.c_str(), O_RDONLY | O_CREAT, 0600);
-    if (new_lock_fd == -1) {
+    lock_fd_ = open(lock_name.c_str(), O_RDONLY | O_CREAT, 0600);
+    if (lock_fd_ == -1) {
         std::string errmsg = strerror(errno);
         isc_throw(SocketError, "cannot create socket lockfile, "
                   << lock_name  << ", : " << errmsg);
     }
 
     // Try to acquire lock. If we can't somebody else is actively
     // using it.
-    int ret = flock(new_lock_fd, LOCK_EX | LOCK_NB);
+    int ret = flock(lock_fd_, LOCK_EX | LOCK_NB);
     if (ret != 0) {
         std::string errmsg = strerror(errno);
-        close(new_lock_fd);
+        close(lock_fd_);
+        lock_fd_ = -1;
         isc_throw(SocketError, "cannot lock socket lockfile, "
                   << lock_name  << ", : " << errmsg);
     }
@@ -597,12 +598,6 @@ UnixCommandMgrImpl::openCommandSocket(const isc::data::ConstElementPtr& socket_i
     LOG_INFO(command_logger, COMMAND_ACCEPTOR_START)
         .arg(socket_name_);
 
-    // Close previous lock to avoid file descriptor leak.
-    if (lock_fd_ != -1) {
-        close(lock_fd_);
-    }
-    lock_fd_ = new_lock_fd;
-
     try {
         // Start asynchronous acceptor service.
         acceptor_.reset(new UnixDomainSocketAcceptor(io_service_));
@@ -639,6 +634,10 @@ UnixCommandMgrImpl::closeCommandSocket() {
     // the server. This connection will be held until the UnixCommandMgr
     // responds to such request.
     connection_pool_.stopAll();
+    if (lock_fd_ != -1) {
+        close(lock_fd_);
+        lock_fd_ = -1;
+    }
 }
 
 void