1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
|
<!DOCTYPE HTML>
<html lang="en" class="light sidebar-visible" dir="ltr">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>Asynchronous I/O - NNG Reference Manual (DRAFT)</title>
<!-- Custom HTML head -->
<meta name="description" content="">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#ffffff">
<link rel="icon" href="../favicon.svg">
<link rel="shortcut icon" href="../favicon.png">
<link rel="stylesheet" href="../css/variables.css">
<link rel="stylesheet" href="../css/general.css">
<link rel="stylesheet" href="../css/chrome.css">
<link rel="stylesheet" href="../css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="../fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" id="highlight-css" href="../highlight.css">
<link rel="stylesheet" id="tomorrow-night-css" href="../tomorrow-night.css">
<link rel="stylesheet" id="ayu-highlight-css" href="../ayu-highlight.css">
<!-- Custom theme stylesheets -->
<link rel="stylesheet" href="../theme/pagetoc.css">
<!-- Provide site root and default themes to javascript -->
<script>
const path_to_root = "../";
const default_light_theme = "light";
const default_dark_theme = "navy";
window.path_to_searchindex_js = "../searchindex.js";
</script>
<!-- Start loading toc.js asap -->
<script src="../toc.js"></script>
</head>
<body>
<div id="mdbook-help-container">
<div id="mdbook-help-popup">
<h2 class="mdbook-help-title">Keyboard shortcuts</h2>
<div>
<p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p>
<p>Press <kbd>S</kbd> or <kbd>/</kbd> to search in the book</p>
<p>Press <kbd>?</kbd> to show this help</p>
<p>Press <kbd>Esc</kbd> to hide this help</p>
</div>
</div>
</div>
<div id="body-container">
<!-- Work around some values being stored in localStorage wrapped in quotes -->
<script>
try {
let theme = localStorage.getItem('mdbook-theme');
let sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') && theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
</script>
<!-- Set the theme before any content is loaded, prevents flash -->
<script>
const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
let theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
const html = document.documentElement;
html.classList.remove('light')
html.classList.add(theme);
html.classList.add("js");
</script>
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
<!-- Hide / unhide sidebar before it is displayed -->
<script>
let sidebar = null;
const sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
} else {
sidebar = 'hidden';
sidebar_toggle.checked = false;
}
if (sidebar === 'visible') {
sidebar_toggle.checked = true;
} else {
html.classList.remove('sidebar-visible');
}
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<!-- populated by js -->
<mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox>
<noscript>
<iframe class="sidebar-iframe-outer" src="../toc.html"></iframe>
</noscript>
<div id="sidebar-resize-handle" class="sidebar-resize-handle">
<div class="sidebar-resize-indicator"></div>
</div>
</nav>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky">
<div class="left-buttons">
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</label>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li>
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search (`/`)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="/ s" aria-controls="searchbar">
<i class="fa fa-search"></i>
</button>
</div>
<h1 class="menu-title">NNG Reference Manual (DRAFT)</h1>
<div class="right-buttons">
<a href="../print.html" title="Print this book" aria-label="Print this book">
<i id="print-button" class="fa fa-print"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<div class="search-wrapper">
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
<div class="spinner-wrapper">
<i class="fa fa-spinner fa-spin"></i>
</div>
</div>
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script>
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<main>
<style>
.mdbook-alerts {
padding: 8px 16px;
margin-bottom: 16px;
border-left: 0.25em solid var(--mdbook-alerts-color);
}
.mdbook-alerts > *:first-child {
margin-top: 0;
}
.mdbook-alerts > *:last-child {
margin-bottom: 0;
}
.mdbook-alerts-title {
display: flex;
font-weight: 600;
align-items: center;
line-height: 1;
color: var(--mdbook-alerts-color);
text-transform: capitalize;
}
.mdbook-alerts-icon {
display: inline-block;
width: 1em;
height: 1em;
margin-right: 0.2em;
background-color: currentColor;
-webkit-mask: no-repeat center / 100%;
mask: no-repeat center / 100%;
-webkit-mask-image: var(--mdbook-alerts-icon);
mask-image: var(--mdbook-alerts-icon);
}
.mdbook-alerts-note {
--mdbook-alerts-color: rgb(9, 105, 218);
/* https://icon-sets.iconify.design/material-symbols/info-outline-rounded/ */
--mdbook-alerts-icon: url('data:image/svg+xml,%3Csvg xmlns="http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg" width="24" height="24" viewBox="0 0 24 24"%3E%3Cpath fill="currentColor" d="M12 17q.425 0 .713-.288T13 16v-4q0-.425-.288-.712T12 11q-.425 0-.712.288T11 12v4q0 .425.288.713T12 17m0-8q.425 0 .713-.288T13 8q0-.425-.288-.712T12 7q-.425 0-.712.288T11 8q0 .425.288.713T12 9m0 13q-2.075 0-3.9-.788t-3.175-2.137q-1.35-1.35-2.137-3.175T2 12q0-2.075.788-3.9t2.137-3.175q1.35-1.35 3.175-2.137T12 2q2.075 0 3.9.788t3.175 2.137q1.35 1.35 2.138 3.175T22 12q0 2.075-.788 3.9t-2.137 3.175q-1.35 1.35-3.175 2.138T12 22m0-2q3.35 0 5.675-2.325T20 12q0-3.35-2.325-5.675T12 4Q8.65 4 6.325 6.325T4 12q0 3.35 2.325 5.675T12 20m0-8"%2F%3E%3C%2Fsvg%3E');
}
.mdbook-alerts-tip {
--mdbook-alerts-color: rgb(26, 127, 55);
/* https://icon-sets.iconify.design/material-symbols/lightbulb-outline-rounded/ */
--mdbook-alerts-icon: url('data:image/svg+xml,%3Csvg xmlns="http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg" width="24" height="24" viewBox="0 0 24 24"%3E%3Cpath fill="currentColor" d="M12 22q-.825 0-1.412-.587T10 20h4q0 .825-.587 1.413T12 22m-3-3q-.425 0-.712-.288T8 18q0-.425.288-.712T9 17h6q.425 0 .713.288T16 18q0 .425-.288.713T15 19zm-.75-3q-1.725-1.025-2.738-2.75T4.5 9.5q0-3.125 2.188-5.312T12 2q3.125 0 5.313 2.188T19.5 9.5q0 2.025-1.012 3.75T15.75 16zm.6-2h6.3q1.125-.8 1.738-1.975T17.5 9.5q0-2.3-1.6-3.9T12 4Q9.7 4 8.1 5.6T6.5 9.5q0 1.35.613 2.525T8.85 14M12 14"%2F%3E%3C%2Fsvg%3E');
}
.mdbook-alerts-important {
--mdbook-alerts-color: rgb(130, 80, 223);
/* https://icon-sets.iconify.design/material-symbols/chat-info-outline-rounded/ */
--mdbook-alerts-icon: url('data:image/svg+xml,%3Csvg xmlns="http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg" width="24" height="24" viewBox="0 0 24 24"%3E%3Cpath fill="currentColor" d="M12 7q.425 0 .713-.288T13 6q0-.425-.288-.712T12 5q-.425 0-.712.288T11 6q0 .425.288.713T12 7m0 8q.425 0 .713-.288T13 14v-4q0-.425-.288-.712T12 9q-.425 0-.712.288T11 10v4q0 .425.288.713T12 15m-6 3l-2.3 2.3q-.475.475-1.088.213T2 19.575V4q0-.825.588-1.412T4 2h16q.825 0 1.413.588T22 4v12q0 .825-.587 1.413T20 18zm-.85-2H20V4H4v13.125zM4 16V4z"%2F%3E%3C%2Fsvg%3E');
}
.mdbook-alerts-warning {
--mdbook-alerts-color: rgb(154, 103, 0);
/* https://icon-sets.iconify.design/material-symbols/warning-outline-rounded/ */
--mdbook-alerts-icon: url('data:image/svg+xml,%3Csvg xmlns="http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg" width="24" height="24" viewBox="0 0 24 24"%3E%3Cpath fill="currentColor" d="M2.725 21q-.275 0-.5-.137t-.35-.363q-.125-.225-.137-.488t.137-.512l9.25-16q.15-.25.388-.375T12 3q.25 0 .488.125t.387.375l9.25 16q.15.25.138.513t-.138.487q-.125.225-.35.363t-.5.137zm1.725-2h15.1L12 6zM12 18q.425 0 .713-.288T13 17q0-.425-.288-.712T12 16q-.425 0-.712.288T11 17q0 .425.288.713T12 18m0-3q.425 0 .713-.288T13 14v-3q0-.425-.288-.712T12 10q-.425 0-.712.288T11 11v3q0 .425.288.713T12 15m0-2.5"%2F%3E%3C%2Fsvg%3E');
}
.mdbook-alerts-caution {
--mdbook-alerts-color: rgb(207, 34, 46);
/* https://icon-sets.iconify.design/material-symbols/brightness-alert-outline-rounded/ */
--mdbook-alerts-icon: url('data:image/svg+xml,%3Csvg xmlns="http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg" width="24" height="24" viewBox="0 0 24 24"%3E%3Cpath fill="currentColor" d="M12 17q.425 0 .713-.288T13 16q0-.425-.288-.712T12 15q-.425 0-.712.288T11 16q0 .425.288.713T12 17m0-4q.425 0 .713-.288T13 12V8q0-.425-.288-.712T12 7q-.425 0-.712.288T11 8v4q0 .425.288.713T12 13m-3.35 7H6q-.825 0-1.412-.587T4 18v-2.65L2.075 13.4q-.275-.3-.425-.662T1.5 12q0-.375.15-.737t.425-.663L4 8.65V6q0-.825.588-1.412T6 4h2.65l1.95-1.925q.3-.275.663-.425T12 1.5q.375 0 .738.15t.662.425L15.35 4H18q.825 0 1.413.588T20 6v2.65l1.925 1.95q.275.3.425.663t.15.737q0 .375-.15.738t-.425.662L20 15.35V18q0 .825-.587 1.413T18 20h-2.65l-1.95 1.925q-.3.275-.662.425T12 22.5q-.375 0-.737-.15t-.663-.425zm.85-2l2.5 2.5l2.5-2.5H18v-3.5l2.5-2.5L18 9.5V6h-3.5L12 3.5L9.5 6H6v3.5L3.5 12L6 14.5V18zm2.5-6"%2F%3E%3C%2Fsvg%3E');
}
</style>
<h1 id="asynchronous-operations"><a class="header" href="#asynchronous-operations">Asynchronous Operations</a></h1>
<p>In order to obtain significant scalability, with low-latency, and minimal
overheads, <em>NNG</em> supports performing operations asynchronously.</p>
<p>One way that applications can perform work asynchronously and concurrently
is by using <a href="../api/thread.html">threads</a>, but threads carry significant resource overheads
and frequently there are limits on the number that can easily be created.</p>
<p>Additionally, with most network applications, the flow of execution will spend
the bulk of its time waiting for traffic from a peer.</p>
<p>For these kinds of applications, it is far more efficient to use asynchronous operations
using the mechanisms described in this chapter.</p>
<div class="mdbook-alerts mdbook-alerts-tip">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
tip
</p>
<p>To get the highest performance with the least overhead, applications should use
asynchronous operations described in this chapter whenever possible.</p>
</div>
<h2 id="asynchronous-io-handle"><a class="header" href="#asynchronous-io-handle">Asynchronous I/O Handle</a></h2>
<pre><code class="language-c">typedef struct nng_aio nng_aio;
</code></pre>
<p>An <a name="a001"></a><code>nng_aio</code><a name="a002"></a> is an opaque structure used in conjunction with
<a name="a003"></a>asynchronous I/O operations.
Every asynchronous operation uses one of these structures, each of which
can only be used with a single operation at a time.</p>
<p>Asynchronous operations are performed without blocking calling application threads.
Instead the application registers a callback function to be executed
when the operation is complete (whether successfully or not).
This callback will be executed exactly once.</p>
<p>The asynchronous I/O framework also supports <a href="../api/aio.html#cancellation">cancellation</a> of
operations that are already in progress as well setting a maximum
<a href="../api/aio.html#set-timeout">timeout</a> for them to complete.</p>
<p>It is also possible to initiate an asynchronous operation, and <a href="../api/aio.html#wait-for-completion">wait</a> for it to
complete, creating a synchronous flow from an asynchronous one.</p>
<h2 id="create-handle"><a class="header" href="#create-handle">Create Handle</a></h2>
<pre><code class="language-c">nng_err nng_aio_alloc(nng_aio **aiop, void (*callb)(void *), void *arg);
</code></pre>
<p>The <a name="a004"></a><code>nng_aio_alloc</code> function creates an <a href="../api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a> object, with the
<a name="a005"></a>callback <em>callb</em> taking the argument <em>arg</em>, and returns it in <em>aiop</em>.</p>
<p>If this succeeds, the function returns zero. Otherwise it may return <a href="../api/errors.html#NNG_ENOMEM"><code>NNG_ENOMEM</code></a>.</p>
<div class="mdbook-alerts mdbook-alerts-tip">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
tip
</p>
<p>The <em>arg</em> should normally be a structure that contains a pointer to the <em>aiop</em>,
or from which it can be located. This allows <em>callb</em> to check the handle for
success using <a href="../api/aio.html#result-of-operation"><code>nng_aio_result</code></a>, as well access other properties of <em>aiop</em>.</p>
</div>
<div class="mdbook-alerts mdbook-alerts-tip">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
tip
</p>
<p>The <em>callb</em> may be executed on another <a href="../api/thread.html">thread</a>, so it may be necessary to use
<a href="../api/synch.html">synchronization</a> methods in <em>callb</em> to avoid data races.</p>
</div>
<h2 id="destroy-handle"><a class="header" href="#destroy-handle">Destroy Handle</a></h2>
<pre><code class="language-c">void nng_aio_free(nng_aio *aio);
void nng_aio_reap(nng_aio *aio);
</code></pre>
<p>The <a name="a006"></a><code>nng_aio_free</code> handle destroys the handle <em>aio</em>, waiting for any operations
and associated callbacks to complete before doing so.</p>
<p>The <a name="a007"></a><code>nng_aio_reap</code> handle destroys the handle <em>aio</em> asynchronously, using a <em>reaper</em>
<a href="../api/thread.html">thread</a> to do so. It does not wait for the object to be destroyed. Thus this function
is safe to call from <em>aio</em>’s own callback.</p>
<div class="mdbook-alerts mdbook-alerts-note">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
note
</p>
<p>The <code>nng_aio_free</code> function must never be called from an <em>aio</em> callback.
Use <code>nng_aio_reap</code> instead if an object must be destroyed from a callback.</p>
</div>
<h2 id="cancellation"><a class="header" href="#cancellation">Cancellation</a></h2>
<pre><code class="language-c">void nng_aio_abort(nng_aio *aio, nng_err err);
void nng_aio_cancel(nng_aio *aio);
void nng_aio_stop(nng_aio *aio);
</code></pre>
<p>These functions are used to stop a previously submitted asynchronous
I/O operation. The operation may be canceled, or may continue to
completion. If no operation is in progress (perhaps because it has
already completed), then these operations have no effect.
If the operation is successfully canceled or aborted, then the callback
will still be called.</p>
<p>The <a name="a008"></a><code>nng_aio_abort</code> function aborts the operation associated with <em>aio</em>
and returns immediately without waiting. If cancellation was successful,
then <a href="../api/aio.html#result-of-operation"><code>nng_aio_result</code></a> will return <em>err</em>.</p>
<p>The <a name="a009"></a><code>nng_aio_cancel</code> function acts like <code>nng_aio_abort</code>, but uses the error code
<a href="../api/errors.html#NNG_ECANCELED"><code>NNG_ECANCELED</code></a><a name="a010"></a>.</p>
<p>The <a name="a011"></a><code>nng_aio_stop</code> function aborts the <em>aio</em> operation with <a href="../api/errors.html#NNG_ESTOPPED"><code>NNG_ESTOPPED</code></a>,
and then waits the operation and any associated callback to complete.
This function also marks <em>aio</em> itself permanently stopped, so that any
new operations scheduled by I/O providers using <a href="../TODO.html"><code>nng_aio_start</code></a>
return false. Thus this function should be used to teardown operations.</p>
<div class="mdbook-alerts mdbook-alerts-tip">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
tip
</p>
<p>When multiple asynchronous I/O handles are in use and need to be
deallocated, it is safest to stop all of them using <code>nng_aio_stop</code>,
before deallocating any of them with <a href="../api/aio.html#destroy-handle"><code>nng_aio_free</code></a>,
particularly if the callbacks might attempt to reschedule further operations.</p>
</div>
<h2 id="set-timeout"><a class="header" href="#set-timeout">Set Timeout</a></h2>
<pre><code class="language-c">void nng_aio_set_timeout(nng_aio *aio, nng_duration timeout);
void nng_aio_set_expire(nng_aio *aio, nng_time expiration);
</code></pre>
<p>The <code>nng_aio_set_timeout</code> function sets a <a name="a012"></a><em>timeout</em>
for the asynchronous operation associated with <em>aio</em>.
This causes a timer to be started when the operation is actually started.
If the timer expires before the operation is completed, then it is
<a href="../api/aio.html#cancellation">aborted</a> with an error of <code>NNG_ETIMEDOUT</code>.
The <em>timeout</em> <a href="../api/time.html">duration</a> is specified as a relative number of milliseconds.</p>
<p>If the timeout is <a href="../api/time.html#duration-type"><code>NNG_DURATION_INFINITE</code></a>, then no timeout is used.
If the timeout is <a href="../api/time.html#duration-type"><code>NNG_DURATION_DEFAULT</code></a>, then a “default” or socket-specific
timeout is used.
(This is frequently the same as <a href="../api/time.html#duration-type"><code>NNG_DURATION_INFINITE</code></a>.)</p>
<p>The <a name="a013"></a><code>nng_aio_set_expire</code> function is similar to <code>nng_aio_set_timeout</code>, but sets
an expiration time based on the system clock. The <em>expiration</em>
<a href="../api/time.html">time</a> is a clock timestamp, such as would be returned by <a href="../api/time.html#get-the-current-time"><code>nng_clock</code></a>.</p>
<h2 id="wait-for-completion"><a class="header" href="#wait-for-completion">Wait for Completion</a></h2>
<pre><code class="language-c">void nng_aio_wait(nng_aio *aio);
</code></pre>
<p>The <a name="a014"></a><code>nng_aio_wait</code> function waits for an asynchronous I/O operation to complete.
If the operation has not been started, or has already completed, then it returns immediately.</p>
<p>If a callback was set with <em>aio</em> when it was allocated, then this
function will not be called until the callback has completed.</p>
<div class="mdbook-alerts mdbook-alerts-important">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
important
</p>
<p>The <code>nng_aio_wait</code> function should never be called from a function that itself
is a callback of an <a href="../api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a>, either this one or any other.
Doing so may result in a deadlock.</p>
</div>
<h2 id="test-for-completion"><a class="header" href="#test-for-completion">Test for Completion</a></h2>
<pre><code class="language-c">bool nng_aio_busy(nng_aio *aio);
</code></pre>
<p>The <a name="a015"></a><code>nng_aio_busy</code> function returns <code>true</code> if the <em>aio</em> is currently busy performing an
operation or is executing a completion callback. Otherwise it return <code>false</code>.
This is the same test used internally by <a href="../api/aio.html#wait-for-completion"><code>nng_aio_wait</code></a>.</p>
<div class="mdbook-alerts mdbook-alerts-important">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
important
</p>
<p>The caller is responsible for coordinating any use of this with any reuse of the <em>aio</em>.
Because the <em>aio</em> can be reused use of this function can be racy.</p>
</div>
<h2 id="result-of-operation"><a class="header" href="#result-of-operation">Result of Operation</a></h2>
<pre><code class="language-c">nng_err nng_aio_result(nng_aio *aio);
size_t nng_aio_count(nng_aio *aio);
</code></pre>
<p>The <a name="a016"></a><code>nng_aio_result</code> function returns the result of the operation associated
with the handle <em>aio</em>.
If the operation was successful, then 0 is returned.
Otherwise a non-zero <a href="../api/errors.html">error</a> code, such as <a href="../api/errors.html#NNG_ECANCELED"><code>NNG_ECANCELED</code></a> or <a href="../api/errors.html#NNG_ETIMEDOUT"><code>NNG_ETIMEDOUT</code></a>, is returned.</p>
<p>For operations that transfer data, <a name="a017"></a><code>nng_aio_count</code> returns the
number of bytes transferred by the operation associated with the handle <em>aio</em>.
Operations that do not transfer data, or do not keep a count, may return zero for this function.</p>
<div class="mdbook-alerts mdbook-alerts-note">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
note
</p>
<p>The return value from these functions is undefined if the operation has not completed yet.
Either call these from the handle’s completion callback, or after waiting for the
operation to complete with <a href="../api/aio.html#wait-for-completion"><code>nng_aio_wait</code></a>.</p>
</div>
<h2 id="messages"><a class="header" href="#messages">Messages</a></h2>
<pre><code class="language-c">nng_msg *nng_aio_get_msg(nng_aio *aio);
void nng_aio_set_msg(nng_aio *aio, nng_msg *msg);
</code></pre>
<p>The <a name="a018"></a><code>nng_aio_get_msg</code> and <a name="a019"></a><code>nng_aio_set_msg</code> functions retrieve and store a <a href="../api/msg.html">message</a>
in <em>aio</em>.
For example, if a function to receive data is called, that function can generally be expected
to store a message on the associated <em>aio</em>, for the application to retrieve with
<code>nng_aio_get_msg</code>.
Conversely an application desiring to send a message <em>msg</em> will store it in the <em>aio</em> using
<code>nng_aio_set_msg</code>. The function implementing the send operation will retrieve the message
and arrange for it to be sent.</p>
<h3 id="message-ownership"><a class="header" href="#message-ownership">Message Ownership</a></h3>
<p>For send or transmit operations, the rule of thumb is that implementation of the operation
is responsible for taking ownership of the message (and releasing resources when it is complete),
if it will return success. If the operation will end in error, then the message will be
retained and it is the consuming application’s responsibility to dispose of the message.
This allows an application the opportunity to reuse the message to try again, if it so desires.</p>
<p>For receive operations, the implementation of the operation will set the message on the <em>aio</em>
on success, and the consuming application hasa responsibility to retrieve and dispose of the
message. Failure to do so will leak the message. If the operation does not complete successfully,
then no message is stored on the <em>aio</em>.</p>
<h2 id="io-vector"><a class="header" href="#io-vector">I/O Vector</a></h2>
<pre><code class="language-c">typedef struct nng_iov {
void * iov_buf;
size_t iov_len;
};
int nng_aio_set_iov(nng_aio *aio, unsigned int niov, nng_iov *iov);
</code></pre>
<p>For some operations, the unit of data transferred is not a <a href="../api/msg.html">message</a>, but
rather a stream of bytes.</p>
<p>For these operations, an array of <em>niov</em> <a name="a020"></a><code>nng_iov</code> structures can be passed to
the <a name="a021"></a><code>nng_aio_set_iov</code> function to provide a scatter/gather array of
elements describing the location (<code>iov_buf</code>) and length (<code>iov_len</code>) of data,
to transfer.</p>
<p>The <em>iov</em> vector is copied into storage in the <em>aio</em> itself, so that callers may use stack allocated <code>nng_iov</code> structures.
The values pointed to by the <code>iov_buf</code> members are <em>not</em> copied by this function though.</p>
<p>A maximum of four (4) <code>nng_iov</code> members may be supplied.</p>
<div class="mdbook-alerts mdbook-alerts-tip">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
tip
</p>
<p>Most functions using <code>nng_iov</code> do not guarantee to transfer all of the data that they
are requested to. To be sure that correct amount of data is transferred, as well as to
start an attempt to complete any partial transfer, check the amount of data transferred by
calling <a href="../api/aio.html#result-of-operation"><code>nng_aio_count</code></a>.</p>
</div>
<h2 id="inputs-and-outputs"><a class="header" href="#inputs-and-outputs">Inputs and Outputs</a></h2>
<pre><code class="language-c">void nng_aio_set_input(nng_aio *aio, unsigned int index, void *param);
void *nng_aio_get_output(nng_aio *aio, unsigned int index);
</code></pre>
<p>Asynchronous operations can take additional input parameters, and
provide additional result outputs besides the <a href="../api/aio.html#result-of-operation">result</a> code.</p>
<p>The <code>nng_aio_set_input</code> function sets the input parameter at <em>index</em>
to <em>param</em> for the operation associated with <em>aio</em>.</p>
<p>The <code>nng_aio_get_output</code> function returns the output result at <em>index</em>
for the operation associated with <em>aio</em>.</p>
<p>The type and semantics of input parameters and output results are determined by specific
operations. The documentation for the operation should provide details.</p>
<p>The valid values of <em>index</em> range from zero (0) to three (3), as no operation
currently defined can accept more than four parameters or return more than four additional
results.</p>
<div class="mdbook-alerts mdbook-alerts-note">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
note
</p>
<p>If the <em>index</em> does not correspond to a defined input for the operation,
then <code>nng_aio_set_input</code> will have no effect, and <code>nng_aio_get_output</code> will
return <code>NULL</code>.</p>
</div>
<div class="mdbook-alerts mdbook-alerts-important">
<p class="mdbook-alerts-title">
<span class="mdbook-alerts-icon"></span>
important
</p>
<p>It is an error to call this function while the <em>aio</em> is currently
in use by an active asynchronous operation.</p>
</div>
<h2 id="scatter-gather-vectors"><a class="header" href="#scatter-gather-vectors">Scatter Gather Vectors</a></h2>
<pre><code class="language-c">typedef struct nng_iov {
void *iov_buf;
size_t iov_len;
} nng_iov;
void nng_aio_set_iov(nng_aio *aio, unsigned nio, const nng_iov *iov);
</code></pre>
<p><a name="a022"></a>
Some asynchronous operations, such as those dealing with <a href="../api/stream.html">streams</a>, use <a name="a023"></a>scatter or <a name="a024"></a>gather
vectors, where data to be transferred is either gathered from multiple separate regions of memory, or
scattered into separate regions of memory. For example a message may have a header located at one location
in memory, and a payload located in another.</p>
<p>The <a name="a025"></a><code>nng_aio_set_iov</code> function configures the <em>aio</em> to use <em>nio</em> separate segments, described by
the elements in <em>iov</em>. For each of these, the segment of size <em>iov_len</em> located at <em>iov_buf</em> will be used.</p>
<p>The elements of <em>iov</em> will be copied into <em>aio</em>, so the vector may be located
on the stack or another temporary location. The locations referenced by it, <em>must</em> remain valid for
the duration of the operation, of course.</p>
<p>Note that many of these operations are not guaranteed to perform a full transfer of data, so even a
successful operation should check the amount of data actually transferred using <a href="../api/aio.html#result-of-operation"><code>nng_aio_count</code></a>,
and if necessary resubmit the operation with a suitably updated vector of <code>nng_iov</code> using this function.</p>
<h2 id="see-also"><a class="header" href="#see-also">See Also</a></h2>
<p><a href="../api/synch.html">Synchronization</a>,
<a href="../api/thread.html">Threads</a>,
<a href="../api/stream.html">Streams</a>,
<a href="../api/time.html">Time</a></p>
<!-- NOTE: This assumes that any page referencing this is located
in a directory two levels down. Meaning ./api/somefile.md or
similar. mdbook cannot accommodate links that are called from
different levels in the hierarchy. -->
<!-- Symbol cross reference -->
<!-- HTTP -->
<!-- HTTP Status -->
<!-- TLS -->
<!-- Macros -->
<!-- Protocols -->
<!-- Transports -->
<!-- Concept index -->
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="../api/url.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="../api/synch.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="../api/url.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="../api/synch.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script>
window.playground_copyable = true;
</script>
<script src="../elasticlunr.min.js"></script>
<script src="../mark.min.js"></script>
<script src="../searcher.js"></script>
<script src="../clipboard.min.js"></script>
<script src="../highlight.js"></script>
<script src="../book.js"></script>
<!-- Custom JS scripts -->
<script src="../theme/pagetoc.js"></script>
</div>
</body>
</html>
|
