[erlang-questions] About erlang:statistics/1 and timeout values

Oscar Hellström <>
Thu Apr 23 14:22:42 CEST 2009


mats cronqvist wrote:
> Oscar Hellström <> writes:
>
>   
>> Hi,
>>
>> I was looking at statistics in the erlang module and found that
>> statistics(runtime) and statistics(wall_clock) returns something called
>> Time_Sinse_Last_Call. I assume that this is "since last call by the
>> calling process" and not a globally kept value. 
>>     
>
>   AFAIK, time since last call is per emulator, not per process. Thus,
>   it is worse than useless.
>
>   mats
>   
Yes, you're right. The call from the spawned process probably happened
after the call from the shell process. This shows the actual behaviour:
29> spawn(fun() -> statistics(wall_clock) end), timer:sleep(10),
statistics(wall_clock).
{1363798390,14}

This is sad though, since it really does make it worse than useless. So,
back to (part of) the original question, how would we go about
decrementing a timeout value between blocking calls. I could use now
diffs, or erlang:start_timer/3... are there better ways?

BTW, what is the difference between erlang:start_timer/3 and
erlang:send_after/3. The documentation looks identical except a weird
detail in the type specification:
erlang:send_after(Time, Dest, Msg) -> TimerRef
...
Dest = pid() | RegName
LocalPid = pid() (of a process, alive or dead, on the local node)

Here LocalPid is never mentioned before...

erlang:start_timer(Time, Dest, Msg) -> TimerRef
...
Dest = LocalPid | RegName
LocalPid = pid() (of a process, alive or dead, on the local node)

This seems to want to say the same thing, but does it correctly.

Thanks

-- 
Oscar Hellström, 
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Mobile: +44 798 45 44 773
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