[lwip-devel] [bug #19167] tcp timeout handler can cause crash being invoked by sys_sem_wait()

[goldsimon]

Follow-up Comment #3, bug #19167 (project lwip):

Executing timeouts only from queues might solve the problem, but it would be
more clear if you could tell the code when you are in a state where you can
execute timeouts.

Using timestamps would be my favourite implementation of timeouts. On
sys_timeout(), you would have to calculate the (absolute) timestamp when this
timeout expires (e.g. 'timeout->expires = sys_time_now()' instead of
'timeout->time = msecs'). Later, in sys_mbox_fetch(), you do something like 

sys_arch_mbox_fetch(mbox, msg, timeouts->next->expires - sys_time_now())

2 downsides of this approach:
- the system has to be time-aware (but it also has to be so, now)
- to prevent time overflow over long time periods, this time would have to be
64-bit... (as we might have to count in miliseconds, 32-bit would overflow in
~50 days)

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