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  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_asio.reference.steady_timer"></a><a class="link" href="steady_timer.html" title="steady_timer">steady_timer</a>
  28 </h3></div></div></div>
  29 <p>
  30         <a class="indexterm" name="boost_asio.indexterm.steady_timer"></a>
  31 Typedef for a timer based on
  32         the steady clock.
  33       </p>
  34 <pre class="programlisting">typedef basic_waitable_timer&lt; chrono::steady_clock &gt; steady_timer;
  35 </pre>
  36 <h5>
  37 <a name="boost_asio.reference.steady_timer.h0"></a>
  38         <span class="phrase"><a name="boost_asio.reference.steady_timer.types"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_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.steady_timer.h1"></a>
 134         <span class="phrase"><a name="boost_asio.reference.steady_timer.member_functions"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_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>
 171                 </p>
 172               </td>
 173 <td>
 174                 <p>
 175                   Constructor. <br> <span class="silver"> &#8212;</span><br> Constructor to set a particular expiry
 176                   time as an absolute time. <br> <span class="silver"> &#8212;</span><br> Constructor to set a particular
 177                   expiry time relative to now. <br> <span class="silver"> &#8212;</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"> &#8212;</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"> &#8212;</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"> &#8212;</span><br> Set the timer's expiry time as an absolute
 232                   time. <br> <span class="silver"> &#8212;</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"> &#8212;</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>
 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.steady_timer.h2"></a>
 331         <span class="phrase"><a name="boost_asio.reference.steady_timer.remarks"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_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">&lt;chrono&gt;</code> facility, or with the Boost.Chrono library.
 336       </p>
 337 <h5>
 338 <a name="boost_asio.reference.steady_timer.h3"></a>
 339         <span class="phrase"><a name="boost_asio.reference.steady_timer.thread_safety"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_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.steady_timer.h4"></a>
 350         <span class="phrase"><a name="boost_asio.reference.steady_timer.examples"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_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.
 356 boost::asio::steady_timer timer(my_context);
 357
 358 // Set an expiry time relative to now.
 359 timer.expires_after(std::chrono::seconds(5));
 360
 361 // Wait for the timer to expire.
 362 timer.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&amp; error)
 368 {
 369   if (!error)
 370   {
 371     // Timer expired.
 372   }
 373 }
 374
 375 ...
 376
 377 // Construct a timer with an absolute expiry time.
 378 boost::asio::steady_timer timer(my_context,
 379     std::chrono::steady_clock::now() + std::chrono::seconds(60));
 380
 381 // Start an asynchronous wait.
 382 timer.async_wait(handler);
 383 </pre>
 384 <h5>
 385 <a name="boost_asio.reference.steady_timer.h5"></a>
 386         <span class="phrase"><a name="boost_asio.reference.steady_timer.changing_an_active_waitable_timer_s_expiry_time"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_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)) &gt; 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
 408 void on_timeout(const boost::system::error_code&amp; 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">&lt;chrono&gt;</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&lt;boost::chrono::steady_clock&gt; timer;
 436 </pre>
 437 <h5>
 438 <a name="boost_asio.reference.steady_timer.h6"></a>
 439         <span class="phrase"><a name="boost_asio.reference.steady_timer.requirements"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.requirements">Requirements</a>
 440       </h5>
 441 <p>
 442         <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/steady_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 &#169; 2003-2019 Christopher M. Kohlhoff<p>
 451         Distributed under the Boost Software License, Version 1.0. (See accompanying
 452         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>)
 453       </p>
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