TUI: Skip redundant "stop" event (macOS kernel panic) (#9007)

When the TUI suspends (:suspend, CTRL-z) it calls tui_terminal_stop (but
does NOT set `ui->data=NULL`, so `tui_is_stopped` returns false). If the
host terminal dies, it sends SIGCONT, SIGHUP (usually in that order):

    ERROR 2018-09-16T19:30:17.065 25821 suspend_event:1153: SIGCONT
    ERROR 2018-09-16T19:30:17.065 25821 on_signal:162: SIGHUP
    ERROR 2018-09-16T19:30:17.155 25821 on_signal:162: SIGHUP

Race: if SIGHUP is handled before SIGCONT, it calls ui_builtin_stop()
which schedules tui_stop before the TUI was resumed?

libuv uv_close() aborts if the handle is already closed/closing.
Somehow that causes macOS to panic. #8075

    Assertion failed: (!uv__is_closing(handle)), function uv_close, file src/unix/core.c, line 117.

    Thread 0:: Dispatch queue: com.apple.main-thread
    0   libsystem_kernel.dylib        	0x00007fff67d69ec2 kevent + 10
    1   libuv.1.dylib                 	0x000000010609304d uv__io_poll + 892
    2   libuv.1.dylib                 	0x0000000106083904 uv_run + 339
    3   nvim                          	0x0000000105e76f7b loop_poll_events + 74
    4   nvim                          	0x0000000105fa5f51 ui_bridge_stop + 206
    5   nvim                          	0x0000000105fa4c00 ui_builtin_stop + 50
    6   nvim                          	0x0000000105f26ee9 mch_exit + 29
    7   nvim                          	0x0000000105eda84a getout + 518
    8   nvim                          	0x0000000105e778b3 multiqueue_process_events + 77
    9   nvim                          	0x0000000105f24c5a os_breakcheck + 49
    10  nvim                          	0x0000000105eb7ea3 auto_next_pat + 463
    11  nvim                          	0x0000000105eb7603 apply_autocmds_group + 1289
    12  nvim                          	0x0000000105eb0e8d apply_autocmds + 36
    13  nvim                          	0x0000000105f5a412 screenalloc + 1892
    14  nvim                          	0x0000000105f5b223 screen_resize + 190
    15  nvim                          	0x0000000105fa52e3 ui_refresh + 257
    16  nvim                          	0x0000000105e8c3d9 do_cmdline + 6614
    17  nvim                          	0x0000000105f03a72 normal_execute + 3996
    18  nvim                          	0x0000000105f89925 state_enter + 164
    19  nvim                          	0x0000000105efe08d normal_enter + 125
    20  nvim                          	0x0000000105ed9ffd main + 6858
    21  libdyld.dylib                 	0x00007fff67c19115 start + 1

    Thread 1 Crashed:
    0   libsystem_kernel.dylib        	0x00007fff67d68e3e __pthread_kill + 10
    1   libsystem_pthread.dylib       	0x00007fff67ea7150 pthread_kill + 333
    2   libsystem_c.dylib             	0x00007fff67cc5312 abort + 127
    3   libsystem_c.dylib             	0x00007fff67c8d368 __assert_rtn + 320
    4   libuv.1.dylib                 	0x00000001060835bf uv_close + 247
    5   nvim                          	0x0000000105fa0ebb tui_terminal_stop + 221
    6   nvim                          	0x0000000105f9ff3d tui_stop + 14
    7   nvim                          	0x0000000105e778b3 multiqueue_process_events + 77
    8   nvim                          	0x0000000105fa0c89 tui_main + 302
    9   libsystem_pthread.dylib       	0x00007fff67ea46c1 _pthread_body + 340
    10  libsystem_pthread.dylib       	0x00007fff67ea456d _pthread_start + 377
    11  libsystem_pthread.dylib       	0x00007fff67ea3c5d thread_start + 13

TODO:
- Set `ui->data = NULL` to flag UI as "stopped"? But loop_poll_events
  drains *all* fast_events, so could skip some events...

0 files changed, 0 insertions, 0 deletions