• akaz (37/37) Jul 21 2012 Hi,

"akaz" <akaz utopia.com> writes:

Hi,

  In Linux kernel programming, there are some parts that are not 
allowed to sleep (to be rescheduled). For example: interrupt 
handlers, softirqs and tasklets.

  Using functions that can sleep (for example: malloc, semaphores, 
regular mutexes - unlike spin_locks, etc.) is forbidden inside 
the above code entities.

  Currently, this is the responsibility of the programmer. I think 
that the compiler itself (the gcc) cannot enforce this as it 
cannot know for sure if a function may block (sleep) or no.

  But, the question is:

  - is there any mechanism in D (maybe  pure?  trusted? 
 notsleeping? or something similar) that could guarantee that a 
function cannot block? (and enforce that all the function called 
from inside that function are not-blocking too). More generally, 
to make such a property transitive and to enforce that?

  A bit off-topic, there is another question, this time concerning 
real-time programming: there are two basic strategies for error 
recovery: forward-recovery (that means, raising an exception and 
saving what can still be saved) and backward-recovery (that 
means, going back in time/code to a recovery point and trying to 
do the job again, maybe using an alternative algorithm).

  The forward-recovery is classic in C++ and D. The 
backward-recovery seems to not be so easy: exceptions can be used 
to detect such an error, but the language itself does not 
provides a way for establishing a recovery point (I think it 
might be seen as a program snapshot) to go back to it and then 
start again (while setting a flag to let "the future" know that 
an error occurred).

  Imagine: trying to compute using one fast algorithm but that 
diverge easily -> failure. Then, roll back and try an alternative 
algorithm, that is more intensive but convergence is guaranteed 
etc. You have to know where to roll back. A simple goto will do 
it?

  Then, the second question is:

  - is there any mechanism in D to provide recovery points?

Thank you.