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    <p>The asio <code>io_service</code> runs in its own thread, once you <em>schedule</em> a timer event, it will call you back at the appropriate time.</p> <p>Here is a complete example:</p> <pre><code>#include &lt;iostream&gt; #include &lt;boost/asio.hpp&gt; #include &lt;boost/bind.hpp&gt; using namespace std; class timed_class { public: timed_class(boost::asio::io_service&amp; io_service) : _timer(io_service) { // now schedule the first timer. _timer.expires_from_now(boost::posix_time::milliseconds(100)); // runs every 100 ms _timer.async_wait(boost::bind(&amp;timed_class::handle_timeout, this, boost::asio::placeholders::error)); } void handle_timeout(boost::system::error_code const&amp; cError) { if (cError.value() == boost::asio::error::operation_aborted) return; if (cError &amp;&amp; cError.value() != boost::asio::error::operation_aborted) return; // throw an exception? cout &lt;&lt; "timer expired" &lt;&lt; endl; // Schedule the timer again... _timer.expires_from_now(boost::posix_time::milliseconds(100)); // runs every 100 ms _timer.async_wait(boost::bind(&amp;timed_class::handle_timeout, this, boost::asio::placeholders::error)); } private: boost::asio::deadline_timer _timer; }; int main(void) { boost::asio::io_service io_service; timed_class t(io_service); io_service.run(); return 0; } </code></pre> <p>EDIT: to dispatch in a separate thread, </p> <pre><code>boost::thread t(boost::bind(&amp;boost::asio::io_service::run, &amp;io_service)); </code></pre> <p>Instead of <code>io_service.run();</code>, now the main thread will continue and once the timeout has expired, then the <code>io_service</code> will call <code>handle_timeout</code></p>
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    1. COThanks for your reply. My question is I need to call the io_service.run() in the main thread. However, in the code between timed_class t(io_service) and io_service.run(), I need to perform other task. If I call io_service.run() first, it would wait for the delay first before performing the task. If I call the function to perform the task before the io_service.run(), I would end up needing to know the time needed for the task to complete to call io_service.run() at appropriate time, which is my original problem. So either way doesn't solve my problem. Or am I missing something? Thanks.
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    2. CO@Ashley, `io_service::run()` is blocking whilst there are events to *dispatch*, if you need to do some setup before the code that needs to be executed periodically, you should do that first then call the `run()` to periodically call the `handle_timer` function. If the code you want to execute *is the code* that needs to be called periodically, put that in a function in the `timed_class`, and then call that in the ctor and the `handle_timeout` body. It may be better if you put some pseudo code of what you want to achieve...
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    3. COThanks for your reply. Let me provide the base case. Let say I need to call functionA only once after 300 ms. I want to pass the functionA into some timer callback which would call that after exactly 300ms (T1), something like what TokenMacGuy's solution provided above. At current time (T0), if I call io_service::run(), it would block until (T1), which is undesirable as I don't want the main thread to block. If I were to call io_service::run() later, I couldn't estimate when is exactly 300 ms later, which is the original problem of calling function after 300 ms.
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