From 9fd19027621fc4f8beb2e57ba37d91465d1906f6 Mon Sep 17 00:00:00 2001 From: Jeff Hostetler Date: Mon, 15 Mar 2021 21:08:27 +0000 Subject: unix-stream-server: create unix domain socket under lock Create a wrapper class for `unix_stream_listen()` that uses a ".lock" lockfile to create the unix domain socket in a race-free manner. Unix domain sockets have a fundamental problem on Unix systems because they persist in the filesystem until they are deleted. This is independent of whether a server is actually listening for connections. Well-behaved servers are expected to delete the socket when they shutdown. A new server cannot easily tell if a found socket is attached to an active server or is leftover cruft from a dead server. The traditional solution used by `unix_stream_listen()` is to force delete the socket pathname and then create a new socket. This solves the latter (cruft) problem, but in the case of the former, it orphans the existing server (by stealing the pathname associated with the socket it is listening on). We cannot directly use a .lock lockfile to create the socket because the socket is created by `bind(2)` rather than the `open(2)` mechanism used by `tempfile.c`. As an alternative, we hold a plain lockfile (".lock") as a mutual exclusion device. Under the lock, we test if an existing socket ("") is has an active server. If not, we create a new socket and begin listening. Then we use "rollback" to delete the lockfile in all cases. This wrapper code conceptually exists at a higher-level than the core unix_stream_connect() and unix_stream_listen() routines that it consumes. It is isolated in a wrapper class for clarity. Signed-off-by: Jeff Hostetler Signed-off-by: Junio C Hamano --- Makefile | 1 + 1 file changed, 1 insertion(+) (limited to 'Makefile') diff --git a/Makefile b/Makefile index 40d5cab78d..f29a9e82e1 100644 --- a/Makefile +++ b/Makefile @@ -1677,6 +1677,7 @@ ifdef NO_UNIX_SOCKETS BASIC_CFLAGS += -DNO_UNIX_SOCKETS else LIB_OBJS += unix-socket.o + LIB_OBJS += unix-stream-server.o endif ifdef USE_WIN32_IPC -- cgit v1.2.3