Hi, I wonder if there has a small cost, little latency and high efficient
solution
of event notification from cgo to go side.
Here is 3 ways as far as I know:
1. Poll
go func() {
for {
// fast ret from cgo
ret := C.sema_try_wait()
if new events {
do_new_event_tasks()
}else{
time.Sleep(time.Millisecond * 250)
}
}
}()
Disadvantage：
Would be some overhead and constant latency.
2. Long wait
go func() {
for {
// maybe blocking at cgo side arbitrarily long time
ret := C.sema_wait()
do_new_event_tasks()
}
}()
Disadvantage：
As been discussed in issue 12416
<https://github.com/golang/go/issues/12416>:
Q: What kind of errors will be returned when a C function takes too long?
>
What is the story with regards to read(2) and blocking devices? (by taruti)
A: In the default mode, nothing will happen if a C function takes too long,
except that your program might eventually run out of memory because the GC
can't run (that won't happen with 1.6 but it might happen in future
> releases).
In the checking mode, you will get a panic. If you want to call a C
> function
that does a read on a device that blocks arbitrarily long, you should read
> the
data into a buffer allocated by C. We will make the syscall.Read function
> do the
right thing on a long-blocking read, whatever that turns out to be.
So, if one cgo call takes too long is not recommend, we still need a cgo
> notify to
go mechanism. (by ianlancetaylor)
So, if the cgo call takes too long to return is not recommend,
we still need another cgo
notify to go mechanism.
3. Raise a signal
c := make(chan os.Signal, 1)
signal.Notify(c, SignalUsr1)
for{
// cgo just raise SignalUsr1 to itself when
// it want to notify go side
s := <-c
do_new_event_tasks()
}
Disadvantage：
A little wierd, and when there is about 100000 new events to
notify per seconds, the overhead would be huge.
Is there some much better methods?
Thanks a lot.
-- Remus
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