Re: [Libguestfs] [PATCH libnbd v3] lib: Atomically update h->state when leaving the locked region.

Split h->state into: - h->public_state = the state on entry to the locked region This is also the atomically, publicly visible state. - h->state = the real current state of the handle When we leave the locked region we update h->public_state with h->state, so that from outside the lock the handle appears to move atomically from its previous state to the final state without going through any intermediate states. Some calls to ‘get_state’ become calls to ‘get_next_state’ if the need the real state. Others which need to see the publicly visible state are changed to ‘get_public_state’. All calls to ‘set_state’ become ‘set_next_state’ because that is the real state that gets updated. The purpose of this patch is to make it easier to reason about the state in lockless code. --- generator/generator | 87 ++++++++++++++++++++++++++++----------------- lib/connect.c | 10 +++--- lib/disconnect.c | 8 ++--- lib/handle.c | 2 +- lib/internal.h | 17 +++++++-- lib/is-state.c | 28 ++++++++------- lib/rw.c | 4 +-- 7 files changed, 97 insertions(+), 59 deletions(-)

@@ -2530,7 +2531,7 @@ let generate_lib_states_c () = pr "{\n"; pr " int r = 0;\n"; pr "\n"; - pr " switch (get_state (h))\n"; + pr " switch (get_next_state (h))\n"; pr " {\n"; List.iter ( fun ({ parsed = { state_enum; events } }) ->