On Sun, Apr 26, 2009 at 12:22 AM, Kimon Simons <kimon.simons@gmail.com> wrote:

Thank you very much Igor.

I acknowledge my ignorence regarding the thread safety issues involved, so I would like dig a little bit deeper here, if you do not mind. If there is a point in the docs that I should be looking and that I have not my apologies. I would appreciate it if you could point me there.

Most of the examples that I have come across for timers have as a precondition that the io_service::run function has been invoked yet; reseting the timer happens withing the timer handler in general.
I am wondering what are the issues involved when calling deadline_timer::async_wait, deadline_timer::cancel for a timer that is associated with an io_service object when io_service::run has already started in a different thread? Or in other words following the point " the io_service may be being run in a background thread that is launched prior to the application's asynchronous operations" in http://www.boost.org/doc/libs/1_38_0/doc/html/boost_asio/reference/io_service.html, how do I launch asynch operations using an io_service that has already being run?

This is relevant to what I really want to do which is:

1.Start io_service::run in one background thread
2.Start async timers on demand from the main thread that should be executed on the io_service::run thread. These timers will be associated with an event that will trigger a thread safe handler on a registerd observer(in this case the Counter class).
3. Modify/cancel from the main thread timers that have outstanding async operations in the io_service::run thread.

In the particular example below, the member function onIncrement of the class Counter is not thread safe, but since the io_service::run is running on a one thread, only one handler will be invoked on the thread that runs io_service::run, so implicitly there is a serialization of access, correct?

My question is what is the best practice, in order to achieve 2 and 3 above? Suprisingly, after building my toy case with your help, the effect is what I expected, but I admit that your comment made me realize that I still need to dig further in order to understand all the issues involved.

I would be grateful for any comment or suggestion.

Thanks a lot.

Kimon

On Sat, Apr 25, 2009 at 8:38 PM, Igor R <boost.lists@gmail.com> wrote:

> m_timer.async_wait(boost::bind(&IntervalEvent::handler, this));

should be: m_timer.async_wait(boost::bind(&IntervalEvent::handler, this, _1));
or:
m_timer.async_wait(boost::bind(&IntervalEvent::handler, this,
boost::asio::placeholders::error));

> void handler(boost::system::error_code& error)

should be: void handler(cosnt boost::system::error_code& error)

> Further to that, I am wondering, in principle should I cancel the deadline_timer on the destructor of the IntervalEvent class? Does the io_service class know when any of the deadline_timers that is being registered goes out of scope?

On destruction, the timer cancels itself anyway.

By the way, you access the timers both from main() and from another
thread - which is illegal, since the asio objects are not thread-safe
(except for io_service).
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