Jepsen: assertion failure in vfs.c

[cole-miller]

This Jepsen job:

https://github.com/canonical/jepsen.dqlite/actions/runs/6950544166/job/18910920901

Tripped this assertion:

dqlite/src/vfs.c

Line 2343 in 09108b8

assert(shm->shared[i] == 0);

[freeekanayaka]

This should be due to the fact that if the process is paused the kernel will still accumulate incoming data in the tcp buffers of open connections, when the process resumes the uv loop might consume that data immediately, without given the monitor_cb function in server.c the chance to run as soon as leadership is lost (because monitor_cb is uv_prepare_t handle callback).

Trying to fire monitor_cb as soon as leadership is lost should fix it, similarly to what was done here cowsql/cowsql#12.