The idea of the handshake timeout is to see if here is any free active thread.
In addition, here are a few fixes that prevent waking up too many threads.
PiperOrigin-RevId: 519871285
In general it is probably a good idea to set a timeout on any futex waits that
the sentry is doing. For now just output some helpful logs about what the shared
memory looks like; in the future we may want to do something more useful on
ETIMEDOUT events.
PiperOrigin-RevId: 518919966
This is the initial implementation of the systrap context queue via a ringbuffer
in shared memory between stub threads and the sentry.
In this new model there is no longer a bound sysmsg thread for every context;
instead each subprocess starts with one initial sysmsg thread, which starts
polling the context queue for new contexts arriving from the sentry. If the
sentry detects that contexts are spending too much time in the context queue
without being processed, it will create new sysmsg threads or wake sleeping
ones. Tangentially, sysmsg threads will go to sleep if they spend too much time
busy looping without new context arrivals.
This model does not yet take into account the full load of the host system or
even multiple subprocesses in the same sandbox. Multiple overloaded subprocesses
are liable to make each other run slower by kicking sysmsg threads more often
than they need to; this will be remedied in follow up CLs.
PiperOrigin-RevId: 516680504
