Logging to one process from thousands: How does it work?

Scott Lystig Fritchie <>
Wed Jan 4 23:37:49 CET 2006

>>>>> "uw" == Ulf Wiger <> writes:

>> How do you implement a bounded queue in Erlang without
>> busy-waiting?

uw> Difficult, but you can achieve back-pressure by making the
uw> communication with the logger synchronous.

How about an unbounded queue that can raise its own priority?  Then we
take advantage of the 'high' vs. 'normal' scheduling behavior.  I
haven't actually tried *compiling* this code, but hopefully it gets
the idea across.

One potential problem could be that my_recursive_func() stops calling
itself before the number of messages in the queue falls below the low
water mark and then keeps its high priority.

-define(WATERMARK_HIGH, 100).
-define(WATERMARK_LOW,    5).

my_recursive_func(MyState) ->
    {message_queue_len, Msgs} = process_info(self(), message_queue_len),
    if Msgs > ?WATERMARK_HIGH -> process_flag(priority, high);
       Msgs < ?WATERMARK_LOW  -> process_flag(priority, normal);
       true                   -> ok
    %% Do real stuff here....


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