Thank you Chet. I proceeded with implementing something that is split up across calls to readline. It's not perfect, and I am writing to you about the problems I faced. I totally understand if you think it's crazy and think I should abandon the effort, but I mostly got it to work.
The current source code is here: https://gitlab.com/shabiel/YDB/-/blob/ydb83_readline/sr_unix/readline.c (it will change a bit in the next few days, but not materially, so you can still refer to it). My approach can be summarized as follows: When I receive a SIGUSR1, siglongjmp to code that does the following: - save the current state using rl_save_state - Copy out the state->buffer and state->prompt - NULL out rl_prompt (otherwise, it gets freed by readline on the next call) - free state->buffer - free state->prompt - Put my buffer and prompt back into the state structure (but I did the allocation and they won't disappear) - unwind the C stack - Call readline again with the following hooks -- startup hook: restore state using rl_restore_state, and set rl_already_prompted to 1. -- redisplay hook: no-op: The text is already on the screen and we don't want it displayed again. I compiled readline from master with -g -O3 so I can see what's going on. Here are the two major issues I faced: 1. I want to call rl_free_line_state after saving state, but doing so, after restoring state, I get a double free warning from ASAN. The undo list is attempted to be freed again: ==68415==ERROR: AddressSanitizer: attempting double-free on 0x603000001ae0 in thread T0: #0 0x7f5e7c27edb8 in __interceptor_free (/usr/lib64/libasan.so.4+0xdbdb8) #1 0x7f5e763cb117 in _rl_free_undo_list ../undo.c:111 #2 0x7f5e763cb178 in rl_free_undo_list ../undo.c:122 #3 0x7f5e763ac32c in readline_internal_teardown ../readline.c:512 #4 0x7f5e763ada1a in readline_internal ../readline.c:734 #5 0x7f5e763ada1a in readline ../readline.c:387 #6 0x7f5e76d2c7ef in readline_read_mval /home/sam/work/gitlab/YDB/sr_unix/readline.c:428 #7 0x7f5e77fa53b7 in op_dmode /home/sam/work/gitlab/YDB/sr_port/op_dmode.c:126 #8 0x7f5e776f0c50 (/home/sam/work/builds/YDB/libyottadb.so+0xfaac50) 0x603000001ae0 is located 0 bytes inside of 32-byte region [0x603000001ae0,0x603000001b00) freed by thread T0 here: #0 0x7f5e7c27edb8 in __interceptor_free (/usr/lib64/libasan.so.4+0xdbdb8) #1 0x7f5e763cb117 in _rl_free_undo_list ../undo.c:111 previously allocated by thread T0 here: #0 0x7f5e7c27f110 in malloc (/usr/lib64/libasan.so.4+0xdc110) 2. If I bypass the readline redisplay, I cannot see any characters being typed. I tried calling rl_reset_terminal and rl_tty_set_echoing to no avail. I think it has to do with internal readline state (maybe it thinks my cursor is somewhere else), but the re-display code is so complex that it's hard for me to tell. Let me know if you have any advice; and if not, that's fine too... I do know what I am doing is crazy, and maybe when we switch in the future to the callback interface, things would be easier and I won't need all of these shenanigans. --Sam ---- On Mon, 25 Sep 2023 09:30:44 -0400 Chet Ramey wrote --- > On 9/21/23 12:34 PM, Sam Habiel wrote: > > Hello there, > > > > Quick Intro: We have an interactive CLI for a language called M used in > > banking and healthcare... I am working on adding readline integration as a > > nice to have feature. We are an open source project located over here: > > https://gitlab.com/YottaDB/DB/YDB. > > > > I sent an earlier message, and I thank Chet for the reply. > > > > I am dealing with the unpleasant for anybody to handle signals. One of our > > signals suspends execution, completely unwinds the C stack (yes, we have > > lots of assembly code for that), and then reissues the prompt. An example > > will help: > > > > YDB>write "fo <<< Receive SIGUSR1 > > > > Once a SIGUSR1 is received, in the background, execution is suspended, a > > custom function is executed, and the entire prompt code is actually > > processed, but the user sees absolutely nothing of that. In the example > > above, the cursor will stay between f and o. Our current code just sets up > > all the prompt data structures from a saved structure when the signal is > > received. > > > > Is this possible with readline()? I naively tried rl_save_state() and > > rl_restore_state(), but that doesn't seem to work. > > > > SIGUSR1 isn't one of the signals readline handles by default, but it has > enough API functions available so that you can do it in your application. > > All the necessary functions are in signals.c. The basic idea is that you > install your signal handler as usual, call the readline functions you > want to restore the terminal and anything else from the handler when it's > safe (look at _rl_signal_handler() for examples), then restore before your > handler returns (look at rl_cleanup_after_signal/rl_restore_after_signal). > > If you want to split it up across calls to readline, you'll have to save > and restore a lot of state. I don't know if the information in > struct readline_state is enough for you -- it depends on your application > needs -- and it's not really intended to save and restore across calls > to readline(). It's mostly intended as a checkpoint during a single call, > so the interaction between the initialization readline does on each > invocation and the state restored isn't well exercised. > > If you want to go further with that approach, you'll need at least a > startup hook to restore the state and do a redisplay before going on > in the second (post-signal) call to readline. > > Chet > > -- > ``The lyf so short, the craft so long to lerne.'' - Chaucer > ``Ars longa, vita brevis'' - Hippocrates > Chet Ramey, UTech, CWRU [email protected] http://tiswww.cwru.edu/~chet/ > >
