stalls with concurrent host name resolvers

Hi,

I discovered that if I have many (say, 50) io_services, and all of  
them perform a name
lookup at (more or less) the same time, some of the handlers will  
stall for about 1 minute. Initially I thought the handlers were never  
called. All host name resolvers resolves the same host name, so only  
the first one should stall (assuming the OS caches host names).

I haven't looked deeper into this, but I did write a small program  
that reproduces the problem (on darwin), see attached.

I realize that this is a very strange use case, since you would  
normally just use a few io_services. The reason I do this is because  
I simulate my component in a bigger network on a single machine, in a  
single process. Each instance then has its own io_service object.

Anyway, this is the output I get:

$time ./bin/darwin-3.3/debug/link-static/test
all threads started

real    1m0.225s
user    0m0.123s
sys     0m0.105s

Increasing the number of threads does not seem to influence the time  
it takes for the stalled lookups.

Maybe this is just an OS issue.

thanks.
--
Arvid Norberg

asio_resolver.cpp
Description: Binary data

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