1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>system_timer</title> 5<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../reference.html" title="Reference"> 9<link rel="prev" href="system_executor.html" title="system_executor"> 10<link rel="next" href="this_coro__executor.html" title="this_coro::executor"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> 15<td align="center"><a href="../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="system_executor.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="this_coro__executor.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_asio.reference.system_timer"></a><a class="link" href="system_timer.html" title="system_timer">system_timer</a> 28</h3></div></div></div> 29<p> 30 <a class="indexterm" name="boost_asio.indexterm.system_timer"></a> 31Typedef for a timer based on 32 the system clock. 33 </p> 34<pre class="programlisting">typedef basic_waitable_timer< chrono::system_clock > system_timer; 35</pre> 36<h5> 37<a name="boost_asio.reference.system_timer.h0"></a> 38 <span class="phrase"><a name="boost_asio.reference.system_timer.types"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.types">Types</a> 39 </h5> 40<div class="informaltable"><table class="table"> 41<colgroup> 42<col> 43<col> 44</colgroup> 45<thead><tr> 46<th> 47 <p> 48 Name 49 </p> 50 </th> 51<th> 52 <p> 53 Description 54 </p> 55 </th> 56</tr></thead> 57<tbody> 58<tr> 59<td> 60 <p> 61 <a class="link" href="basic_waitable_timer__rebind_executor.html" title="basic_waitable_timer::rebind_executor"><span class="bold"><strong>rebind_executor</strong></span></a> 62 </p> 63 </td> 64<td> 65 <p> 66 Rebinds the timer type to another executor. 67 </p> 68 </td> 69</tr> 70<tr> 71<td> 72 <p> 73 <a class="link" href="basic_waitable_timer/clock_type.html" title="basic_waitable_timer::clock_type"><span class="bold"><strong>clock_type</strong></span></a> 74 </p> 75 </td> 76<td> 77 <p> 78 The clock type. 79 </p> 80 </td> 81</tr> 82<tr> 83<td> 84 <p> 85 <a class="link" href="basic_waitable_timer/duration.html" title="basic_waitable_timer::duration"><span class="bold"><strong>duration</strong></span></a> 86 </p> 87 </td> 88<td> 89 <p> 90 The duration type of the clock. 91 </p> 92 </td> 93</tr> 94<tr> 95<td> 96 <p> 97 <a class="link" href="basic_waitable_timer/executor_type.html" title="basic_waitable_timer::executor_type"><span class="bold"><strong>executor_type</strong></span></a> 98 </p> 99 </td> 100<td> 101 <p> 102 The type of the executor associated with the object. 103 </p> 104 </td> 105</tr> 106<tr> 107<td> 108 <p> 109 <a class="link" href="basic_waitable_timer/time_point.html" title="basic_waitable_timer::time_point"><span class="bold"><strong>time_point</strong></span></a> 110 </p> 111 </td> 112<td> 113 <p> 114 The time point type of the clock. 115 </p> 116 </td> 117</tr> 118<tr> 119<td> 120 <p> 121 <a class="link" href="basic_waitable_timer/traits_type.html" title="basic_waitable_timer::traits_type"><span class="bold"><strong>traits_type</strong></span></a> 122 </p> 123 </td> 124<td> 125 <p> 126 The wait traits type. 127 </p> 128 </td> 129</tr> 130</tbody> 131</table></div> 132<h5> 133<a name="boost_asio.reference.system_timer.h1"></a> 134 <span class="phrase"><a name="boost_asio.reference.system_timer.member_functions"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.member_functions">Member 135 Functions</a> 136 </h5> 137<div class="informaltable"><table class="table"> 138<colgroup> 139<col> 140<col> 141</colgroup> 142<thead><tr> 143<th> 144 <p> 145 Name 146 </p> 147 </th> 148<th> 149 <p> 150 Description 151 </p> 152 </th> 153</tr></thead> 154<tbody> 155<tr> 156<td> 157 <p> 158 <a class="link" href="basic_waitable_timer/async_wait.html" title="basic_waitable_timer::async_wait"><span class="bold"><strong>async_wait</strong></span></a> 159 </p> 160 </td> 161<td> 162 <p> 163 Start an asynchronous wait on the timer. 164 </p> 165 </td> 166</tr> 167<tr> 168<td> 169 <p> 170 <a class="link" href="basic_waitable_timer/basic_waitable_timer.html" title="basic_waitable_timer::basic_waitable_timer"><span class="bold"><strong>basic_waitable_timer</strong></span></a> <span class="silver">[constructor]</span> 171 </p> 172 </td> 173<td> 174 <p> 175 Constructor. <br> <span class="silver"> —</span><br> Constructor to set a particular expiry 176 time as an absolute time. <br> <span class="silver"> —</span><br> Constructor to set a particular 177 expiry time relative to now. <br> <span class="silver"> —</span><br> Move-construct a basic_waitable_timer 178 from another. 179 </p> 180 </td> 181</tr> 182<tr> 183<td> 184 <p> 185 <a class="link" href="basic_waitable_timer/cancel.html" title="basic_waitable_timer::cancel"><span class="bold"><strong>cancel</strong></span></a> 186 </p> 187 </td> 188<td> 189 <p> 190 Cancel any asynchronous operations that are waiting on the timer. 191 <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) Cancel 192 any asynchronous operations that are waiting on the timer. 193 </p> 194 </td> 195</tr> 196<tr> 197<td> 198 <p> 199 <a class="link" href="basic_waitable_timer/cancel_one.html" title="basic_waitable_timer::cancel_one"><span class="bold"><strong>cancel_one</strong></span></a> 200 </p> 201 </td> 202<td> 203 <p> 204 Cancels one asynchronous operation that is waiting on the timer. 205 <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) Cancels 206 one asynchronous operation that is waiting on the timer. 207 </p> 208 </td> 209</tr> 210<tr> 211<td> 212 <p> 213 <a class="link" href="basic_waitable_timer/expires_after.html" title="basic_waitable_timer::expires_after"><span class="bold"><strong>expires_after</strong></span></a> 214 </p> 215 </td> 216<td> 217 <p> 218 Set the timer's expiry time relative to now. 219 </p> 220 </td> 221</tr> 222<tr> 223<td> 224 <p> 225 <a class="link" href="basic_waitable_timer/expires_at.html" title="basic_waitable_timer::expires_at"><span class="bold"><strong>expires_at</strong></span></a> 226 </p> 227 </td> 228<td> 229 <p> 230 (Deprecated: Use expiry().) Get the timer's expiry time as an absolute 231 time. <br> <span class="silver"> —</span><br> Set the timer's expiry time as an absolute 232 time. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) 233 Set the timer's expiry time as an absolute time. 234 </p> 235 </td> 236</tr> 237<tr> 238<td> 239 <p> 240 <a class="link" href="basic_waitable_timer/expires_from_now.html" title="basic_waitable_timer::expires_from_now"><span class="bold"><strong>expires_from_now</strong></span></a> 241 </p> 242 </td> 243<td> 244 <p> 245 (Deprecated: Use expiry().) Get the timer's expiry time relative 246 to now. <br> <span class="silver"> —</span><br> (Deprecated: Use expires_after().) Set the 247 timer's expiry time relative to now. 248 </p> 249 </td> 250</tr> 251<tr> 252<td> 253 <p> 254 <a class="link" href="basic_waitable_timer/expiry.html" title="basic_waitable_timer::expiry"><span class="bold"><strong>expiry</strong></span></a> 255 </p> 256 </td> 257<td> 258 <p> 259 Get the timer's expiry time as an absolute time. 260 </p> 261 </td> 262</tr> 263<tr> 264<td> 265 <p> 266 <a class="link" href="basic_waitable_timer/get_executor.html" title="basic_waitable_timer::get_executor"><span class="bold"><strong>get_executor</strong></span></a> 267 </p> 268 </td> 269<td> 270 <p> 271 Get the executor associated with the object. 272 </p> 273 </td> 274</tr> 275<tr> 276<td> 277 <p> 278 <a class="link" href="basic_waitable_timer/operator_eq_.html" title="basic_waitable_timer::operator="><span class="bold"><strong>operator=</strong></span></a> 279 </p> 280 </td> 281<td> 282 <p> 283 Move-assign a basic_waitable_timer from another. 284 </p> 285 </td> 286</tr> 287<tr> 288<td> 289 <p> 290 <a class="link" href="basic_waitable_timer/wait.html" title="basic_waitable_timer::wait"><span class="bold"><strong>wait</strong></span></a> 291 </p> 292 </td> 293<td> 294 <p> 295 Perform a blocking wait on the timer. 296 </p> 297 </td> 298</tr> 299<tr> 300<td> 301 <p> 302 <a class="link" href="basic_waitable_timer/_basic_waitable_timer.html" title="basic_waitable_timer::~basic_waitable_timer"><span class="bold"><strong>~basic_waitable_timer</strong></span></a> <span class="silver">[destructor]</span> 303 </p> 304 </td> 305<td> 306 <p> 307 Destroys the timer. 308 </p> 309 </td> 310</tr> 311</tbody> 312</table></div> 313<p> 314 The <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput">basic_waitable_timer</code></a> 315 class template provides the ability to perform a blocking or asynchronous 316 wait for a timer to expire. 317 </p> 318<p> 319 A waitable timer is always in one of two states: "expired" or "not 320 expired". If the <code class="computeroutput">wait()</code> or <code class="computeroutput">async_wait()</code> function 321 is called on an expired timer, the wait operation will complete immediately. 322 </p> 323<p> 324 Most applications will use one of the <a class="link" href="steady_timer.html" title="steady_timer"><code class="computeroutput">steady_timer</code></a>, 325 <a class="link" href="system_timer.html" title="system_timer"><code class="computeroutput">system_timer</code></a> 326 or <a class="link" href="high_resolution_timer.html" title="high_resolution_timer"><code class="computeroutput">high_resolution_timer</code></a> 327 typedefs. 328 </p> 329<h5> 330<a name="boost_asio.reference.system_timer.h2"></a> 331 <span class="phrase"><a name="boost_asio.reference.system_timer.remarks"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.remarks">Remarks</a> 332 </h5> 333<p> 334 This waitable timer functionality is for use with the C++11 standard library's 335 <code class="computeroutput"><chrono></code> facility, or with the Boost.Chrono library. 336 </p> 337<h5> 338<a name="boost_asio.reference.system_timer.h3"></a> 339 <span class="phrase"><a name="boost_asio.reference.system_timer.thread_safety"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.thread_safety">Thread 340 Safety</a> 341 </h5> 342<p> 343 <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe. 344 </p> 345<p> 346 <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Unsafe. 347 </p> 348<h5> 349<a name="boost_asio.reference.system_timer.h4"></a> 350 <span class="phrase"><a name="boost_asio.reference.system_timer.examples"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.examples">Examples</a> 351 </h5> 352<p> 353 Performing a blocking wait (C++11): 354 </p> 355<pre class="programlisting">// Construct a timer without setting an expiry time. 356boost::asio::steady_timer timer(my_context); 357 358// Set an expiry time relative to now. 359timer.expires_after(std::chrono::seconds(5)); 360 361// Wait for the timer to expire. 362timer.wait(); 363</pre> 364<p> 365 Performing an asynchronous wait (C++11): 366 </p> 367<pre class="programlisting">void handler(const boost::system::error_code& error) 368{ 369 if (!error) 370 { 371 // Timer expired. 372 } 373} 374 375... 376 377// Construct a timer with an absolute expiry time. 378boost::asio::steady_timer timer(my_context, 379 std::chrono::steady_clock::now() + std::chrono::seconds(60)); 380 381// Start an asynchronous wait. 382timer.async_wait(handler); 383</pre> 384<h5> 385<a name="boost_asio.reference.system_timer.h5"></a> 386 <span class="phrase"><a name="boost_asio.reference.system_timer.changing_an_active_waitable_timer_s_expiry_time"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.changing_an_active_waitable_timer_s_expiry_time">Changing 387 an active waitable timer's expiry time</a> 388 </h5> 389<p> 390 Changing the expiry time of a timer while there are pending asynchronous 391 waits causes those wait operations to be cancelled. To ensure that the action 392 associated with the timer is performed only once, use something like this: 393 used: 394 </p> 395<pre class="programlisting">void on_some_event() 396{ 397 if (my_timer.expires_after(seconds(5)) > 0) 398 { 399 // We managed to cancel the timer. Start new asynchronous wait. 400 my_timer.async_wait(on_timeout); 401 } 402 else 403 { 404 // Too late, timer has already expired! 405 } 406} 407 408void on_timeout(const boost::system::error_code& e) 409{ 410 if (e != boost::asio::error::operation_aborted) 411 { 412 // Timer was not cancelled, take necessary action. 413 } 414} 415</pre> 416<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 417<li class="listitem"> 418 The <code class="computeroutput">boost::asio::basic_waitable_timer::expires_after()</code> function 419 cancels any pending asynchronous waits, and returns the number of asynchronous 420 waits that were cancelled. If it returns 0 then you were too late and 421 the wait handler has already been executed, or will soon be executed. 422 If it returns 1 then the wait handler was successfully cancelled. 423 </li> 424<li class="listitem"> 425 If a wait handler is cancelled, the boost::system::error_code passed 426 to it contains the value <code class="computeroutput">boost::asio::error::operation_aborted</code>. 427 </li> 428</ul></div> 429<p> 430 This typedef uses the C++11 <code class="computeroutput"><chrono></code> standard library 431 facility, if available. Otherwise, it may use the Boost.Chrono library. To 432 explicitly utilise Boost.Chrono, use the <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput">basic_waitable_timer</code></a> 433 template directly: 434 </p> 435<pre class="programlisting">typedef basic_waitable_timer<boost::chrono::system_clock> timer; 436</pre> 437<h5> 438<a name="boost_asio.reference.system_timer.h6"></a> 439 <span class="phrase"><a name="boost_asio.reference.system_timer.requirements"></a></span><a class="link" href="system_timer.html#boost_asio.reference.system_timer.requirements">Requirements</a> 440 </h5> 441<p> 442 <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/system_timer.hpp</code> 443 </p> 444<p> 445 <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code> 446 </p> 447</div> 448<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 449<td align="left"></td> 450<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 451 Kohlhoff<p> 452 Distributed under the Boost Software License, Version 1.0. (See accompanying 453 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 454 </p> 455</div></td> 456</tr></table> 457<hr> 458<div class="spirit-nav"> 459<a accesskey="p" href="system_executor.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="this_coro__executor.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 460</div> 461</body> 462</html> 463
