forked from anfeng/zeromq
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathzmq_socket.html
1424 lines (1360 loc) · 34.8 KB
/
zmq_socket.html
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
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<meta name="generator" content="AsciiDoc 8.5.2" />
<title>zmq_socket(3)</title>
<style type="text/css">
/* Debug borders */
p, li, dt, dd, div, pre, h1, h2, h3, h4, h5, h6 {
/*
border: 1px solid red;
*/
}
body {
margin: 1em 5% 1em 5%;
}
a {
color: blue;
text-decoration: underline;
}
a:visited {
color: fuchsia;
}
em {
font-style: italic;
color: navy;
}
strong {
font-weight: bold;
color: #083194;
}
tt {
color: navy;
}
h1, h2, h3, h4, h5, h6 {
color: #527bbd;
font-family: sans-serif;
margin-top: 1.2em;
margin-bottom: 0.5em;
line-height: 1.3;
}
h1, h2, h3 {
border-bottom: 2px solid silver;
}
h2 {
padding-top: 0.5em;
}
h3 {
float: left;
}
h3 + * {
clear: left;
}
div.sectionbody {
font-family: serif;
margin-left: 0;
}
hr {
border: 1px solid silver;
}
p {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
ul, ol, li > p {
margin-top: 0;
}
pre {
padding: 0;
margin: 0;
}
span#author {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
font-size: 1.1em;
}
span#email {
}
span#revnumber, span#revdate, span#revremark {
font-family: sans-serif;
}
div#footer {
font-family: sans-serif;
font-size: small;
border-top: 2px solid silver;
padding-top: 0.5em;
margin-top: 4.0em;
}
div#footer-text {
float: left;
padding-bottom: 0.5em;
}
div#footer-badges {
float: right;
padding-bottom: 0.5em;
}
div#preamble {
margin-top: 1.5em;
margin-bottom: 1.5em;
}
div.tableblock, div.imageblock, div.exampleblock, div.verseblock,
div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
div.admonitionblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.admonitionblock {
margin-top: 2.0em;
margin-bottom: 2.0em;
margin-right: 10%;
color: #606060;
}
div.content { /* Block element content. */
padding: 0;
}
/* Block element titles. */
div.title, caption.title {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
text-align: left;
margin-top: 1.0em;
margin-bottom: 0.5em;
}
div.title + * {
margin-top: 0;
}
td div.title:first-child {
margin-top: 0.0em;
}
div.content div.title:first-child {
margin-top: 0.0em;
}
div.content + div.title {
margin-top: 0.0em;
}
div.sidebarblock > div.content {
background: #ffffee;
border: 1px solid silver;
padding: 0.5em;
}
div.listingblock > div.content {
border: 1px solid silver;
background: #f4f4f4;
padding: 0.5em;
}
div.quoteblock, div.verseblock {
padding-left: 1.0em;
margin-left: 1.0em;
margin-right: 10%;
border-left: 5px solid #dddddd;
color: #777777;
}
div.quoteblock > div.attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock > div.content {
white-space: pre;
}
div.verseblock > div.attribution {
padding-top: 0.75em;
text-align: left;
}
/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
div.verseblock + div.attribution {
text-align: left;
}
div.admonitionblock .icon {
vertical-align: top;
font-size: 1.1em;
font-weight: bold;
text-decoration: underline;
color: #527bbd;
padding-right: 0.5em;
}
div.admonitionblock td.content {
padding-left: 0.5em;
border-left: 3px solid #dddddd;
}
div.exampleblock > div.content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
div.imageblock div.content { padding-left: 0; }
span.image img { border-style: none; }
a.image:visited { color: white; }
dl {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
dt {
margin-top: 0.5em;
margin-bottom: 0;
font-style: normal;
color: navy;
}
dd > *:first-child {
margin-top: 0.1em;
}
ul, ol {
list-style-position: outside;
}
ol.arabic {
list-style-type: decimal;
}
ol.loweralpha {
list-style-type: lower-alpha;
}
ol.upperalpha {
list-style-type: upper-alpha;
}
ol.lowerroman {
list-style-type: lower-roman;
}
ol.upperroman {
list-style-type: upper-roman;
}
div.compact ul, div.compact ol,
div.compact p, div.compact p,
div.compact div, div.compact div {
margin-top: 0.1em;
margin-bottom: 0.1em;
}
div.tableblock > table {
border: 3px solid #527bbd;
}
thead, p.table.header {
font-family: sans-serif;
font-weight: bold;
}
tfoot {
font-weight: bold;
}
td > div.verse {
white-space: pre;
}
p.table {
margin-top: 0;
}
/* Because the table frame attribute is overriden by CSS in most browsers. */
div.tableblock > table[frame="void"] {
border-style: none;
}
div.tableblock > table[frame="hsides"] {
border-left-style: none;
border-right-style: none;
}
div.tableblock > table[frame="vsides"] {
border-top-style: none;
border-bottom-style: none;
}
div.hdlist {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
div.hdlist tr {
padding-bottom: 15px;
}
dt.hdlist1.strong, td.hdlist1.strong {
font-weight: bold;
}
td.hdlist1 {
vertical-align: top;
font-style: normal;
padding-right: 0.8em;
color: navy;
}
td.hdlist2 {
vertical-align: top;
}
div.hdlist.compact tr {
margin: 0;
padding-bottom: 0;
}
.comment {
background: yellow;
}
.footnote, .footnoteref {
font-size: 0.8em;
}
span.footnote, span.footnoteref {
vertical-align: super;
}
#footnotes {
margin: 20px 0 20px 0;
padding: 7px 0 0 0;
}
#footnotes div.footnote {
margin: 0 0 5px 0;
}
#footnotes hr {
border: none;
border-top: 1px solid silver;
height: 1px;
text-align: left;
margin-left: 0;
width: 20%;
min-width: 100px;
}
@media print {
div#footer-badges { display: none; }
}
div#toc {
margin-bottom: 2.5em;
}
div#toctitle {
color: #527bbd;
font-family: sans-serif;
font-size: 1.1em;
font-weight: bold;
margin-top: 1.0em;
margin-bottom: 0.1em;
}
div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
margin-top: 0;
margin-bottom: 0;
}
div.toclevel2 {
margin-left: 2em;
font-size: 0.9em;
}
div.toclevel3 {
margin-left: 4em;
font-size: 0.9em;
}
div.toclevel4 {
margin-left: 6em;
font-size: 0.9em;
}
/* Overrides for manpage documents */
h1 {
padding-top: 0.5em;
padding-bottom: 0.5em;
border-top: 2px solid silver;
border-bottom: 2px solid silver;
}
h2 {
border-style: none;
}
div.sectionbody {
margin-left: 5%;
}
@media print {
div#toc { display: none; }
}
/* Workarounds for IE6's broken and incomplete CSS2. */
div.sidebar-content {
background: #ffffee;
border: 1px solid silver;
padding: 0.5em;
}
div.sidebar-title, div.image-title {
color: #527bbd;
font-family: sans-serif;
font-weight: bold;
margin-top: 0.0em;
margin-bottom: 0.5em;
}
div.listingblock div.content {
border: 1px solid silver;
background: #f4f4f4;
padding: 0.5em;
}
div.quoteblock-attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock-content {
white-space: pre;
}
div.verseblock-attribution {
padding-top: 0.75em;
text-align: left;
}
div.exampleblock-content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
/* IE6 sets dynamically generated links as visited. */
div#toc a:visited { color: blue; }
</style>
<script type="text/javascript">
/*<+'])');
// Function that scans the DOM tree for header elements (the DOM2
// nodeIterator API would be a better technique but not supported by all
// browsers).
var iterate = function (el) {
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 1 /* Node.ELEMENT_NODE */) {
var mo = re.exec(i.tagName);
if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
}
iterate(i);
}
}
}
iterate(el);
return result;
}
var toc = document.getElementById("toc");
var entries = tocEntries(document.getElementById("content"), toclevels);
for (var i = 0; i < entries.length; ++i) {
var entry = entries[i];
if (entry.element.id == "")
entry.element.id = "_toc_" + i;
var a = document.createElement("a");
a.href = "#" + entry.element.id;
a.appendChild(document.createTextNode(entry.text));
var div = document.createElement("div");
div.appendChild(a);
div.className = "toclevel" + entry.toclevel;
toc.appendChild(div);
}
if (entries.length == 0)
toc.parentNode.removeChild(toc);
},
/////////////////////////////////////////////////////////////////////
// Footnotes generator
/////////////////////////////////////////////////////////////////////
/* Based on footnote generation code from:
* http://www.brandspankingnew.net/archive/2005/07/format_footnote.html
*/
footnotes: function () {
var cont = document.getElementById("content");
var noteholder = document.getElementById("footnotes");
var spans = cont.getElementsByTagName("span");
var refs = {};
var n = 0;
for (i=0; i<spans.length; i++) {
if (spans[i].className == "footnote") {
n++;
// Use [\s\S] in place of . so multi-line matches work.
// Because JavaScript has no s (dotall) regex flag.
note = spans[i].innerHTML.match(/\s*\[([\s\S]*)]\s*/)[1];
noteholder.innerHTML +=
"<div class='footnote' id='_footnote_" + n + "'>" +
"<a href='#_footnoteref_" + n + "' title='Return to text'>" +
n + "</a>. " + note + "</div>";
spans[i].innerHTML =
"[<a id='_footnoteref_" + n + "' href='#_footnote_" + n +
"' title='View footnote' class='footnote'>" + n + "</a>]";
var id =spans[i].getAttribute("id");
if (id != null) refs["#"+id] = n;
}
}
if (n == 0)
noteholder.parentNode.removeChild(noteholder);
else {
// Process footnoterefs.
for (i=0; i<spans.length; i++) {
if (spans[i].className == "footnoteref") {
var href = spans[i].getElementsByTagName("a")[0].getAttribute("href");
href = href.match(/#.*/)[0]; // Because IE return full URL.
n = refs[href];
spans[i].innerHTML =
"[<a href='#_footnote_" + n +
"' title='View footnote' class='footnote'>" + n + "</a>]";
}
}
}
}
}
/*]]>*/
</script>
</head>
<body>
<div id="header">
<h1>
zmq_socket(3) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>zmq_socket -
create 0MQ socket
</p>
</div>
</div>
<div id="content">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="paragraph"><p><strong>void *zmq_socket (void <em>*context</em>, int <em>type</em>);</strong></p></div>
</div>
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>The <em>zmq_socket()</em> function shall create a ØMQ socket within the specified
<em>context</em> and return an opaque handle to the newly created socket. The <em>type</em>
argument specifies the socket type, which determines the semantics of
communication over the socket.</p></div>
<div class="paragraph"><p>The newly created socket is initially unbound, and not associated with any
endpoints. In order to establish a message flow a socket must first be
connected to at least one endpoint with <a href="zmq_connect.html">zmq_connect(3)</a>, or at least one
endpoint must be created for accepting incoming connections with
<a href="zmq_bind.html">zmq_bind(3)</a>.</p></div>
<div class="paragraph"><div class="title">Key differences to conventional sockets</div><p>Generally speaking, conventional sockets present a <em>synchronous</em> interface to
either connection-oriented reliable byte streams (SOCK_STREAM), or
connection-less unreliable datagrams (SOCK_DGRAM). In comparison, ØMQ sockets
present an abstraction of an asynchronous <em>message queue</em>, with the exact
queueing semantics depending on the socket type in use. Where conventional
sockets transfer streams of bytes or discrete datagrams, ØMQ sockets transfer
discrete <em>messages</em>.</p></div>
<div class="paragraph"><p>ØMQ sockets being <em>asynchronous</em> means that the timings of the physical
connection setup and tear down, reconnect and effective delivery are transparent
to the user and organized by ØMQ itself. Further, messages may be <em>queued</em> in
the event that a peer is unavailable to receive them.</p></div>
<div class="paragraph"><p>Conventional sockets allow only strict one-to-one (two peers), many-to-one
(many clients, one server), or in some cases one-to-many (multicast)
relationships. With the exception of <em>ZMQ_PAIR</em>, ØMQ sockets may be connected
<strong>to multiple endpoints</strong> using <em>zmq_connect()</em>, while simultaneously accepting
incoming connections <strong>from multiple endpoints</strong> bound to the socket using
<em>zmq_bind()</em>, thus allowing many-to-many relationships.</p></div>
<div class="paragraph"><div class="title">Thread safety</div><p>ØMQ <em>sockets</em> are <em>not</em> thread safe. Applications MUST NOT use a socket
from multiple threads except after migrating a socket from one thread to
another with a "full fence" memory barrier.</p></div>
<div class="paragraph"><div class="title">Socket types</div><p>The following sections present the socket types defined by ØMQ, grouped by the
general <em>messaging pattern</em> which is built from related socket types.</p></div>
<h3 id="_request_reply_pattern">Request-reply pattern</h3><div style="clear:left"></div>
<div class="paragraph"><p>The request-reply pattern is used for sending requests from a <em>client</em> to one
or more instances of a <em>service</em>, and receiving subsequent replies to each
request sent.</p></div>
<h4 id="_zmq_req">ZMQ_REQ</h4>
<div class="paragraph"><p>A socket of type <em>ZMQ_REQ</em> is used by a <em>client</em> to send requests to and
receive replies from a <em>service</em>. This socket type allows only an alternating
sequence of <em>zmq_send(request)</em> and subsequent <em>zmq_recv(reply)</em> calls. Each
request sent is load-balanced among all <em>services</em>, and each reply received is
matched with the last issued request.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_REQ</em> socket enters an exceptional state due to having reached the
high water mark for all <em>services</em>, or if there are no <em>services</em> at all, then
any <a href="zmq_send.html">zmq_send(3)</a> operations on the socket shall block until the
exceptional state ends or at least one <em>service</em> becomes available for sending;
messages are not discarded.</p></div>
<div class="hdlist"><div class="title">Summary of ZMQ_REQ characteristics</div><table>
<tr>
<td class="hdlist1">
Compatible peer sockets
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
<em>ZMQ_REP</em>
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Direction
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Bidirectional
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Send/receive pattern
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Send, Receive, Send, Receive, …
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Outgoing routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Load-balanced
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Incoming routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Last peer
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
ZMQ_HWM option action
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Block
</p>
</td>
</tr>
</table></div>
<h4 id="_zmq_rep">ZMQ_REP</h4>
<div class="paragraph"><p>A socket of type <em>ZMQ_REP</em> is used by a <em>service</em> to receive requests from and
send replies to a <em>client</em>. This socket type allows only an alternating
sequence of <em>zmq_recv(request)</em> and subsequent <em>zmq_send(reply)</em> calls. Each
request received is fair-queued from among all <em>clients</em>, and each reply sent
is routed to the <em>client</em> that issued the last request. If the original
requester doesn’t exist any more the reply is silently discarded.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_REP</em> socket enters an exceptional state due to having reached the
high water mark for a <em>client</em>, then any replies sent to the <em>client</em> in
question shall be dropped until the exceptional state ends.</p></div>
<div class="hdlist"><div class="title">Summary of ZMQ_REP characteristics</div><table>
<tr>
<td class="hdlist1">
Compatible peer sockets
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
<em>ZMQ_REQ</em>
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Direction
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Bidirectional
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Send/receive pattern
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Receive, Send, Receive, Send, …
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Incoming routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Fair-queued
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Outgoing routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Last peer
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
ZMQ_HWM option action
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Drop
</p>
</td>
</tr>
</table></div>
<h4 id="_zmq_dealer">ZMQ_DEALER</h4>
<div class="paragraph"><p>A socket of type <em>ZMQ_DEALER</em> is an advanced pattern used for extending
request/reply sockets. Each message sent is load-balanced among all connected
peers, and each message received is fair-queued from all connected peers.</p></div>
<div class="paragraph"><p>Previously this socket was called <em>ZMQ_XREQ</em> and that name remains available
for backwards compatibility.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_DEALER</em> socket enters an exceptional state due to having reached the
high water mark for all peers, or if there are no peers at all, then any
<a href="zmq_send.html">zmq_send(3)</a> operations on the socket shall block until the exceptional
state ends or at least one peer becomes available for sending; messages are not
discarded.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_DEALER</em> socket is connected to a <em>ZMQ_REP</em> socket each message sent
must consist of an empty message part, the <em>delimiter</em>, followed by one or more
<em>body parts</em>.</p></div>
<div class="hdlist"><div class="title">Summary of ZMQ_DEALER characteristics</div><table>
<tr>
<td class="hdlist1">
Compatible peer sockets
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
<em>ZMQ_ROUTER</em>, <em>ZMQ_REP</em>
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Direction
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Bidirectional
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Send/receive pattern
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Unrestricted
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Outgoing routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Load-balanced
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Incoming routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Fair-queued
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
ZMQ_HWM option action
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Block
</p>
</td>
</tr>
</table></div>
<h4 id="_zmq_router">ZMQ_ROUTER</h4>
<div class="paragraph"><p>A socket of type <em>ZMQ_ROUTER</em> is an advanced pattern used for extending
request/reply sockets. When receiving messages a <em>ZMQ_ROUTER</em> socket shall
prepend a message part containing the <em>identity</em> of the originating peer to the
message before passing it to the application. Messages received are fair-queued
from among all connected peers. When sending messages a <em>ZMQ_ROUTER</em> socket shall
remove the first part of the message and use it to determine the <em>identity</em> of
the peer the message shall be routed to. If the peer does not exist anymore
the message shall be silently discarded.</p></div>
<div class="paragraph"><p>Previously this socket was called <em>ZMQ_XREP</em> and that name remains available
for backwards compatibility.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_ROUTER</em> socket enters an exceptional state due to having reached the
high water mark for all peers, or if there are no peers at all, then any
messages sent to the socket shall be dropped until the exceptional state ends.
Likewise, any messages routed to a non-existent peer or a peer for which the
individual high water mark has been reached shall also be dropped.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_REQ</em> socket is connected to a <em>ZMQ_ROUTER</em> socket, in addition to the
<em>identity</em> of the originating peer each message received shall contain an empty
<em>delimiter</em> message part. Hence, the entire structure of each received message
as seen by the application becomes: one or more <em>identity</em> parts, <em>delimiter</em>
part, one or more <em>body parts</em>. When sending replies to a <em>ZMQ_REQ</em> socket the
application must include the <em>delimiter</em> part.</p></div>
<div class="hdlist"><div class="title">Summary of ZMQ_ROUTER characteristics</div><table>
<tr>
<td class="hdlist1">
Compatible peer sockets
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
<em>ZMQ_DEALER</em>, <em>ZMQ_REQ</em>
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Direction
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Bidirectional
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Send/receive pattern
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Unrestricted
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Outgoing routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
See text
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Incoming routing strategy
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Fair-queued
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
ZMQ_HWM option action
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Drop
</p>
</td>
</tr>
</table></div>
<h3 id="_publish_subscribe_pattern">Publish-subscribe pattern</h3><div style="clear:left"></div>
<div class="paragraph"><p>The publish-subscribe pattern is used for one-to-many distribution of data from
a single <em>publisher</em> to multiple <em>subscribers</em> in a fan out fashion.</p></div>
<h4 id="_zmq_pub">ZMQ_PUB</h4>
<div class="paragraph"><p>A socket of type <em>ZMQ_PUB</em> is used by a <em>publisher</em> to distribute data.
Messages sent are distributed in a fan out fashion to all connected peers.
The <a href="zmq_recv.html">zmq_recv(3)</a> function is not implemented for this socket type.</p></div>
<div class="paragraph"><p>When a <em>ZMQ_PUB</em> socket enters an exceptional state due to having reached the
high water mark for a <em>subscriber</em>, then any messages that would be sent to the
<em>subscriber</em> in question shall instead be dropped until the exceptional state
ends. The <em>zmq_send()</em> function shall never block for this socket type.</p></div>
<div class="hdlist"><div class="title">Summary of ZMQ_PUB characteristics</div><table>
<tr>
<td class="hdlist1">
Compatible peer sockets
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
<em>ZMQ_SUB</em>
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Direction
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Unidirectional
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Send/receive pattern
<br />
</td>
<td class="hdlist2">
<p style="margin-top: 0;">
Send only
</p>
</td>
</tr>
<tr>
<td class="hdlist1">
Incoming routing strategy