Boost Users :
Subject: Re: [Boost-users] [Asio] run_one does not seem to run signal handler but run does
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2015-03-01 17:29:22
On 1/03/2015 15:39, Robert Valkenburg wrote:
> I don't understand why io_service.run() says 6 handlers where invoked
> but otherwise it seems OK.
> Now if i replace io_service.run() with io_service.run_one() i
> expected the handler to be invoked once when CNTR C is pressed. Here
> is the output
> This suggests one handler was invoked which is what i might have expected.
> This does not have a line with >1 indicating entering the handler and
> there is no output from the handler and count remains at 0.
"One handler" does not necessarily mean "one application code handler".
Many high-level async operations are actually composed internally of a
sequence of lower-level operations. As such, it may require multiple
internal handler calls before your user-level handler is actually called.
From your output, it appears that it your case it actually requires two
handler calls to actually invoke your application handler. However you
should not rely on this as it may change if the internals of Asio change
or if some other condition in your execution environment changes.
run_one() is intended to be called in a loop with other "idle" work --
but using run() is preferred whenever you can just post the extra work
to the io_service anyway.
Note that an async_wait is a single-shot thing anyway -- if you didn't
call async_wait again in your handler then it would only catch the
signal once, if that's what you're trying to do.
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