The current SEGV handling on posix is not useful: as soon as our handler
is left, it's triggered again, infinitely.
This patch changes to restore the original handler, so the OS can create
a core dump, etc.
This moves the hysteresis test out of the systemlib and makes it its own
small library. Since it still depends on hrt_absolute_time this does not
link yet. My attempt to get all link dependencies together failed.
This makes sure we add the lockstep_scheduler_test even if the
ENABLE_LOCKSTEP_SCHEDULER is not set to yes. This means the
lockstep_scheduler is not used for SITL but the CMakeLists.txt file
still used and the test added.
This fixes build races which happened if "Unix Makefiles" instead of
ninja-build was used as the cmake backend.
For any dependencies of commands on files we need to create a target.
Otherwise, if "Unix Makefiles" are used as the generator the commands
are run in parallel on the different files which often can lead to
races or redundancies in our build.
A nice write-up can be found here:
https://samthursfield.wordpress.com/2015/11/21/
cmake-dependencies-between-targets-and-files-and-custom-commands/#
custom-commands-and-parallel-make
It turns out that we can fix the unit tests of the lockstep_scheduler
just by checking if `passed_lock` is not `nullptr`.
Without this check, the unit tests segfaulted.
This solves a potential dead-lock when trying to shutdown: a call to exit()
stops all threads and calls all destructors for static objects.
The destructor of LockstepScheduler takes a lock. However this is not
safe, as the lock could already be taken (by any thread).
Some threads do not exit and are still running when
trying to exit SITL running under Windows in Cygwin.
This problem was introduced with:
- posix shell #10173 because of strating a child process
for the startup script and mixing up the signal handling
(only Ctrl+C broken)
- lockstep #10648 because of simulator threads not
stopping gracefully anymore with timing race conditions
(no graceful exit possible anymore)
I leave the SIGINT handler on its default implementation for
Cygwin which kills the process and all its threads when pressing
Ctrl+C.
This hotfix at least allows the usage of Ctrl+C again instead
of forcing the user to use the task manager to shut down
px4.exe going crazy on CPU load instead of exiting
everytime.
