1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>io_context</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="invalid_service_owner/invalid_service_owner.html" title="invalid_service_owner::invalid_service_owner"> 10<link rel="next" href="io_context/add_service.html" title="io_context::add_service"> 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="invalid_service_owner/invalid_service_owner.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="io_context/add_service.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.io_context"></a><a class="link" href="io_context.html" title="io_context">io_context</a> 28</h3></div></div></div> 29<p> 30 Provides core I/O functionality. 31 </p> 32<pre class="programlisting">class io_context : 33 public execution_context 34</pre> 35<h5> 36<a name="boost_asio.reference.io_context.h0"></a> 37 <span class="phrase"><a name="boost_asio.reference.io_context.types"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.types">Types</a> 38 </h5> 39<div class="informaltable"><table class="table"> 40<colgroup> 41<col> 42<col> 43</colgroup> 44<thead><tr> 45<th> 46 <p> 47 Name 48 </p> 49 </th> 50<th> 51 <p> 52 Description 53 </p> 54 </th> 55</tr></thead> 56<tbody> 57<tr> 58<td> 59 <p> 60 <a class="link" href="io_context__basic_executor_type.html" title="io_context::basic_executor_type"><span class="bold"><strong>basic_executor_type</strong></span></a> 61 </p> 62 </td> 63<td> 64 <p> 65 Executor implementation type used to submit functions to an io_context. 66 </p> 67 </td> 68</tr> 69<tr> 70<td> 71 <p> 72 <a class="link" href="io_context__service.html" title="io_context::service"><span class="bold"><strong>service</strong></span></a> 73 </p> 74 </td> 75<td> 76 <p> 77 Base class for all io_context services. 78 </p> 79 </td> 80</tr> 81<tr> 82<td> 83 <p> 84 <a class="link" href="io_context__strand.html" title="io_context::strand"><span class="bold"><strong>strand</strong></span></a> 85 </p> 86 </td> 87<td> 88 <p> 89 Provides serialised handler execution. 90 </p> 91 </td> 92</tr> 93<tr> 94<td> 95 <p> 96 <a class="link" href="io_context__work.html" title="io_context::work"><span class="bold"><strong>work</strong></span></a> 97 </p> 98 </td> 99<td> 100 <p> 101 (Deprecated: Use executor_work_guard.) Class to inform the io_context 102 when it has work to do. 103 </p> 104 </td> 105</tr> 106<tr> 107<td> 108 <p> 109 <a class="link" href="io_context/count_type.html" title="io_context::count_type"><span class="bold"><strong>count_type</strong></span></a> 110 </p> 111 </td> 112<td> 113 <p> 114 The type used to count the number of handlers executed by the context. 115 </p> 116 </td> 117</tr> 118<tr> 119<td> 120 <p> 121 <a class="link" href="io_context/executor_type.html" title="io_context::executor_type"><span class="bold"><strong>executor_type</strong></span></a> 122 </p> 123 </td> 124<td> 125 <p> 126 Executor used to submit functions to an io_context. 127 </p> 128 </td> 129</tr> 130<tr> 131<td> 132 <p> 133 <a class="link" href="io_context/fork_event.html" title="io_context::fork_event"><span class="bold"><strong>fork_event</strong></span></a> 134 </p> 135 </td> 136<td> 137 <p> 138 Fork-related event notifications. 139 </p> 140 </td> 141</tr> 142</tbody> 143</table></div> 144<h5> 145<a name="boost_asio.reference.io_context.h1"></a> 146 <span class="phrase"><a name="boost_asio.reference.io_context.member_functions"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.member_functions">Member 147 Functions</a> 148 </h5> 149<div class="informaltable"><table class="table"> 150<colgroup> 151<col> 152<col> 153</colgroup> 154<thead><tr> 155<th> 156 <p> 157 Name 158 </p> 159 </th> 160<th> 161 <p> 162 Description 163 </p> 164 </th> 165</tr></thead> 166<tbody> 167<tr> 168<td> 169 <p> 170 <a class="link" href="io_context/dispatch.html" title="io_context::dispatch"><span class="bold"><strong>dispatch</strong></span></a> 171 </p> 172 </td> 173<td> 174 <p> 175 (Deprecated: Use boost::asio::dispatch().) Request the io_context 176 to invoke the given handler. 177 </p> 178 </td> 179</tr> 180<tr> 181<td> 182 <p> 183 <a class="link" href="io_context/get_executor.html" title="io_context::get_executor"><span class="bold"><strong>get_executor</strong></span></a> 184 </p> 185 </td> 186<td> 187 <p> 188 Obtains the executor associated with the io_context. 189 </p> 190 </td> 191</tr> 192<tr> 193<td> 194 <p> 195 <a class="link" href="io_context/io_context.html" title="io_context::io_context"><span class="bold"><strong>io_context</strong></span></a> <span class="silver">[constructor]</span> 196 </p> 197 </td> 198<td> 199 <p> 200 Constructor. 201 </p> 202 </td> 203</tr> 204<tr> 205<td> 206 <p> 207 <a class="link" href="io_context/notify_fork.html" title="io_context::notify_fork"><span class="bold"><strong>notify_fork</strong></span></a> 208 </p> 209 </td> 210<td> 211 <p> 212 Notify the execution_context of a fork-related event. 213 </p> 214 </td> 215</tr> 216<tr> 217<td> 218 <p> 219 <a class="link" href="io_context/poll.html" title="io_context::poll"><span class="bold"><strong>poll</strong></span></a> 220 </p> 221 </td> 222<td> 223 <p> 224 Run the io_context object's event processing loop to execute ready 225 handlers. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) 226 Run the io_context object's event processing loop to execute ready 227 handlers. 228 </p> 229 </td> 230</tr> 231<tr> 232<td> 233 <p> 234 <a class="link" href="io_context/poll_one.html" title="io_context::poll_one"><span class="bold"><strong>poll_one</strong></span></a> 235 </p> 236 </td> 237<td> 238 <p> 239 Run the io_context object's event processing loop to execute one 240 ready handler. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) 241 Run the io_context object's event processing loop to execute one 242 ready handler. 243 </p> 244 </td> 245</tr> 246<tr> 247<td> 248 <p> 249 <a class="link" href="io_context/post.html" title="io_context::post"><span class="bold"><strong>post</strong></span></a> 250 </p> 251 </td> 252<td> 253 <p> 254 (Deprecated: Use boost::asio::post().) Request the io_context to 255 invoke the given handler and return immediately. 256 </p> 257 </td> 258</tr> 259<tr> 260<td> 261 <p> 262 <a class="link" href="io_context/reset.html" title="io_context::reset"><span class="bold"><strong>reset</strong></span></a> 263 </p> 264 </td> 265<td> 266 <p> 267 (Deprecated: Use restart().) Reset the io_context in preparation 268 for a subsequent run() invocation. 269 </p> 270 </td> 271</tr> 272<tr> 273<td> 274 <p> 275 <a class="link" href="io_context/restart.html" title="io_context::restart"><span class="bold"><strong>restart</strong></span></a> 276 </p> 277 </td> 278<td> 279 <p> 280 Restart the io_context in preparation for a subsequent run() invocation. 281 </p> 282 </td> 283</tr> 284<tr> 285<td> 286 <p> 287 <a class="link" href="io_context/run.html" title="io_context::run"><span class="bold"><strong>run</strong></span></a> 288 </p> 289 </td> 290<td> 291 <p> 292 Run the io_context object's event processing loop. <br> <span class="silver"> —</span><br> 293 (Deprecated: Use non-error_code overload.) Run the io_context object's 294 event processing loop. 295 </p> 296 </td> 297</tr> 298<tr> 299<td> 300 <p> 301 <a class="link" href="io_context/run_for.html" title="io_context::run_for"><span class="bold"><strong>run_for</strong></span></a> 302 </p> 303 </td> 304<td> 305 <p> 306 Run the io_context object's event processing loop for a specified 307 duration. 308 </p> 309 </td> 310</tr> 311<tr> 312<td> 313 <p> 314 <a class="link" href="io_context/run_one.html" title="io_context::run_one"><span class="bold"><strong>run_one</strong></span></a> 315 </p> 316 </td> 317<td> 318 <p> 319 Run the io_context object's event processing loop to execute at 320 most one handler. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code 321 overlaod.) Run the io_context object's event processing loop to 322 execute at most one handler. 323 </p> 324 </td> 325</tr> 326<tr> 327<td> 328 <p> 329 <a class="link" href="io_context/run_one_for.html" title="io_context::run_one_for"><span class="bold"><strong>run_one_for</strong></span></a> 330 </p> 331 </td> 332<td> 333 <p> 334 Run the io_context object's event processing loop for a specified 335 duration to execute at most one handler. 336 </p> 337 </td> 338</tr> 339<tr> 340<td> 341 <p> 342 <a class="link" href="io_context/run_one_until.html" title="io_context::run_one_until"><span class="bold"><strong>run_one_until</strong></span></a> 343 </p> 344 </td> 345<td> 346 <p> 347 Run the io_context object's event processing loop until a specified 348 time to execute at most one handler. 349 </p> 350 </td> 351</tr> 352<tr> 353<td> 354 <p> 355 <a class="link" href="io_context/run_until.html" title="io_context::run_until"><span class="bold"><strong>run_until</strong></span></a> 356 </p> 357 </td> 358<td> 359 <p> 360 Run the io_context object's event processing loop until a specified 361 time. 362 </p> 363 </td> 364</tr> 365<tr> 366<td> 367 <p> 368 <a class="link" href="io_context/stop.html" title="io_context::stop"><span class="bold"><strong>stop</strong></span></a> 369 </p> 370 </td> 371<td> 372 <p> 373 Stop the io_context object's event processing loop. 374 </p> 375 </td> 376</tr> 377<tr> 378<td> 379 <p> 380 <a class="link" href="io_context/stopped.html" title="io_context::stopped"><span class="bold"><strong>stopped</strong></span></a> 381 </p> 382 </td> 383<td> 384 <p> 385 Determine whether the io_context object has been stopped. 386 </p> 387 </td> 388</tr> 389<tr> 390<td> 391 <p> 392 <a class="link" href="io_context/wrap.html" title="io_context::wrap"><span class="bold"><strong>wrap</strong></span></a> 393 </p> 394 </td> 395<td> 396 <p> 397 (Deprecated: Use boost::asio::bind_executor().) Create a new handler 398 that automatically dispatches the wrapped handler on the io_context. 399 </p> 400 </td> 401</tr> 402<tr> 403<td> 404 <p> 405 <a class="link" href="io_context/_io_context.html" title="io_context::~io_context"><span class="bold"><strong>~io_context</strong></span></a> <span class="silver">[destructor]</span> 406 </p> 407 </td> 408<td> 409 <p> 410 Destructor. 411 </p> 412 </td> 413</tr> 414</tbody> 415</table></div> 416<h5> 417<a name="boost_asio.reference.io_context.h2"></a> 418 <span class="phrase"><a name="boost_asio.reference.io_context.protected_member_functions"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.protected_member_functions">Protected 419 Member Functions</a> 420 </h5> 421<div class="informaltable"><table class="table"> 422<colgroup> 423<col> 424<col> 425</colgroup> 426<thead><tr> 427<th> 428 <p> 429 Name 430 </p> 431 </th> 432<th> 433 <p> 434 Description 435 </p> 436 </th> 437</tr></thead> 438<tbody> 439<tr> 440<td> 441 <p> 442 <a class="link" href="io_context/destroy.html" title="io_context::destroy"><span class="bold"><strong>destroy</strong></span></a> 443 </p> 444 </td> 445<td> 446 <p> 447 Destroys all services in the context. 448 </p> 449 </td> 450</tr> 451<tr> 452<td> 453 <p> 454 <a class="link" href="io_context/shutdown.html" title="io_context::shutdown"><span class="bold"><strong>shutdown</strong></span></a> 455 </p> 456 </td> 457<td> 458 <p> 459 Shuts down all services in the context. 460 </p> 461 </td> 462</tr> 463</tbody> 464</table></div> 465<h5> 466<a name="boost_asio.reference.io_context.h3"></a> 467 <span class="phrase"><a name="boost_asio.reference.io_context.friends"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.friends">Friends</a> 468 </h5> 469<div class="informaltable"><table class="table"> 470<colgroup> 471<col> 472<col> 473</colgroup> 474<thead><tr> 475<th> 476 <p> 477 Name 478 </p> 479 </th> 480<th> 481 <p> 482 Description 483 </p> 484 </th> 485</tr></thead> 486<tbody> 487<tr> 488<td> 489 <p> 490 <a class="link" href="io_context/add_service.html" title="io_context::add_service"><span class="bold"><strong>add_service</strong></span></a> 491 </p> 492 </td> 493<td> 494 <p> 495 (Deprecated: Use make_service().) Add a service object to the execution_context. 496 </p> 497 </td> 498</tr> 499<tr> 500<td> 501 <p> 502 <a class="link" href="io_context/has_service.html" title="io_context::has_service"><span class="bold"><strong>has_service</strong></span></a> 503 </p> 504 </td> 505<td> 506 <p> 507 Determine if an execution_context contains a specified service 508 type. 509 </p> 510 </td> 511</tr> 512<tr> 513<td> 514 <p> 515 <a class="link" href="io_context/make_service.html" title="io_context::make_service"><span class="bold"><strong>make_service</strong></span></a> 516 </p> 517 </td> 518<td> 519 <p> 520 Creates a service object and adds it to the execution_context. 521 </p> 522 </td> 523</tr> 524<tr> 525<td> 526 <p> 527 <a class="link" href="io_context/use_service.html" title="io_context::use_service"><span class="bold"><strong>use_service</strong></span></a> 528 </p> 529 </td> 530<td> 531 <p> 532 <br> <span class="silver"> —</span><br> Obtain the service object corresponding to the given 533 type. 534 </p> 535 </td> 536</tr> 537</tbody> 538</table></div> 539<p> 540 The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 541 class provides the core I/O functionality for users of the asynchronous I/O 542 objects, including: 543 </p> 544<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 545<li class="listitem"> 546 <code class="computeroutput">boost::asio::ip::tcp::socket</code> 547 </li> 548<li class="listitem"> 549 <code class="computeroutput">boost::asio::ip::tcp::acceptor</code> 550 </li> 551<li class="listitem"> 552 <code class="computeroutput">boost::asio::ip::udp::socket</code> 553 </li> 554<li class="listitem"> 555 <a class="link" href="deadline_timer.html" title="deadline_timer"><code class="computeroutput">deadline_timer</code></a>. 556 </li> 557</ul></div> 558<p> 559 The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 560 class also includes facilities intended for developers of custom asynchronous 561 services. 562 </p> 563<h5> 564<a name="boost_asio.reference.io_context.h4"></a> 565 <span class="phrase"><a name="boost_asio.reference.io_context.thread_safety"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.thread_safety">Thread 566 Safety</a> 567 </h5> 568<p> 569 <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe. 570 </p> 571<p> 572 <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Safe, with the 573 specific exceptions of the <code class="computeroutput">restart()</code> and <code class="computeroutput">notify_fork()</code> 574 functions. Calling <code class="computeroutput">restart()</code> while there are unfinished <code class="computeroutput">run()</code>, 575 <code class="computeroutput">run_one()</code>, <code class="computeroutput">run_for()</code>, <code class="computeroutput">run_until()</code>, 576 <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code> calls results in undefined 577 behaviour. The <code class="computeroutput">notify_fork()</code> function should not be called while 578 any <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 579 function, or any function on an I/O object that is associated with the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>, 580 is being called in another thread. 581 </p> 582<h5> 583<a name="boost_asio.reference.io_context.h5"></a> 584 <span class="phrase"><a name="boost_asio.reference.io_context.synchronous_and_asynchronous_operations"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.synchronous_and_asynchronous_operations">Synchronous 585 and asynchronous operations</a> 586 </h5> 587<p> 588 Synchronous operations on I/O objects implicitly run the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 589 object for an individual operation. The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 590 functions <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>, <code class="computeroutput">run_for()</code>, 591 <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code> 592 must be called for the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 593 to perform asynchronous operations on behalf of a C++ program. Notification 594 that an asynchronous operation has completed is delivered by invocation of 595 the associated handler. Handlers are invoked only by a thread that is currently 596 calling any overload of <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>, <code class="computeroutput">run_for()</code>, 597 <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code> 598 for the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>. 599 </p> 600<h5> 601<a name="boost_asio.reference.io_context.h6"></a> 602 <span class="phrase"><a name="boost_asio.reference.io_context.effect_of_exceptions_thrown_from_handlers"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.effect_of_exceptions_thrown_from_handlers">Effect 603 of exceptions thrown from handlers</a> 604 </h5> 605<p> 606 If an exception is thrown from a handler, the exception is allowed to propagate 607 through the throwing thread's invocation of <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>, 608 <code class="computeroutput">run_for()</code>, <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or 609 <code class="computeroutput">poll_one()</code>. No other threads that are calling any of these functions 610 are affected. It is then the responsibility of the application to catch the 611 exception. 612 </p> 613<p> 614 After the exception has been caught, the <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>, 615 <code class="computeroutput">run_for()</code>, <code class="computeroutput">run_until()</code>, <code class="computeroutput">poll()</code> or 616 <code class="computeroutput">poll_one()</code> call may be restarted <span class="emphasis"><em>without</em></span> 617 the need for an intervening call to <code class="computeroutput">restart()</code>. This allows the 618 thread to rejoin the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 619 object's thread pool without impacting any other threads in the pool. 620 </p> 621<p> 622 For example: 623 </p> 624<pre class="programlisting">boost::asio::io_context io_context; 625... 626for (;;) 627{ 628 try 629 { 630 io_context.run(); 631 break; // run() exited normally 632 } 633 catch (my_exception& e) 634 { 635 // Deal with exception as appropriate. 636 } 637} 638</pre> 639<h5> 640<a name="boost_asio.reference.io_context.h7"></a> 641 <span class="phrase"><a name="boost_asio.reference.io_context.submitting_arbitrary_tasks_to_the_io_context"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.submitting_arbitrary_tasks_to_the_io_context">Submitting 642 arbitrary tasks to the io_context</a> 643 </h5> 644<p> 645 To submit functions to the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>, 646 use the <a class="link" href="dispatch.html" title="dispatch"><code class="computeroutput">dispatch</code></a> 647 , <a class="link" href="post.html" title="post"><code class="computeroutput">post</code></a> or 648 <a class="link" href="defer.html" title="defer"><code class="computeroutput">defer</code></a> free 649 functions. 650 </p> 651<p> 652 For example: 653 </p> 654<pre class="programlisting">void my_task() 655{ 656 ... 657} 658 659... 660 661boost::asio::io_context io_context; 662 663// Submit a function to the io_context. 664boost::asio::post(io_context, my_task); 665 666// Submit a lambda object to the io_context. 667boost::asio::post(io_context, 668 []() 669 { 670 ... 671 }); 672 673// Run the io_context until it runs out of work. 674io_context.run(); 675</pre> 676<h5> 677<a name="boost_asio.reference.io_context.h8"></a> 678 <span class="phrase"><a name="boost_asio.reference.io_context.stopping_the_io_context_from_running_out_of_work"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.stopping_the_io_context_from_running_out_of_work">Stopping 679 the io_context from running out of work</a> 680 </h5> 681<p> 682 Some applications may need to prevent an <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 683 object's <code class="computeroutput">run()</code> call from returning when there is no more work 684 to do. For example, the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 685 may be being run in a background thread that is launched prior to the application's 686 asynchronous operations. The <code class="computeroutput">run()</code> call may be kept running 687 by creating an executor that tracks work against the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a>: 688 </p> 689<pre class="programlisting">boost::asio::io_context io_context; 690auto work = boost::asio::require(io_context.get_executor(), 691 boost::asio::execution::outstanding_work.tracked); 692... 693</pre> 694<p> 695 If using C++03, which lacks automatic variable type deduction, you may compute 696 the return type of the require call: 697 </p> 698<pre class="programlisting">boost::asio::io_context io_context; 699typename boost::asio::require_result< 700 boost::asio::io_context::executor_type, 701 boost::asio::exeution::outstanding_work_t::tracked_t> 702 work = boost::asio::require(io_context.get_executor(), 703 boost::asio::execution::outstanding_work.tracked); 704... 705</pre> 706<p> 707 or store the result in the type-erasing executor wrapper, any_io_executor: 708 </p> 709<pre class="programlisting">boost::asio::io_context io_context; 710boost::asio::any_io_executor work 711 = boost::asio::require(io_context.get_executor(), 712 boost::asio::execution::outstanding_work.tracked); 713... 714</pre> 715<p> 716 To effect a shutdown, the application will then need to call the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 717 object's <code class="computeroutput">stop()</code> member function. This will cause the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput">io_context</code></a> 718 <code class="computeroutput">run()</code> call to return as soon as possible, abandoning unfinished 719 operations and without permitting ready handlers to be dispatched. 720 </p> 721<p> 722 Alternatively, if the application requires that all operations and handlers 723 be allowed to finish normally, store the work-tracking executor in an any_io_executor 724 object, so that it may be explicitly reset. 725 </p> 726<pre class="programlisting">boost::asio::io_context io_context; 727boost::asio::any_io_executor work 728 = boost::asio::require(io_context.get_executor(), 729 boost::asio::execution::outstanding_work.tracked); 730... 731work = boost::asio::any_io_executor(); // Allow run() to exit. 732</pre> 733<h5> 734<a name="boost_asio.reference.io_context.h9"></a> 735 <span class="phrase"><a name="boost_asio.reference.io_context.requirements"></a></span><a class="link" href="io_context.html#boost_asio.reference.io_context.requirements">Requirements</a> 736 </h5> 737<p> 738 <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/io_context.hpp</code> 739 </p> 740<p> 741 <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code> 742 </p> 743</div> 744<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 745<td align="left"></td> 746<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 747 Kohlhoff<p> 748 Distributed under the Boost Software License, Version 1.0. (See accompanying 749 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>) 750 </p> 751</div></td> 752</tr></table> 753<hr> 754<div class="spirit-nav"> 755<a accesskey="p" href="invalid_service_owner/invalid_service_owner.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="io_context/add_service.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 756</div> 757</body> 758</html> 759
