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Revision 1.9 by root, Fri Nov 23 16:17:12 2007 UTC vs.
Revision 1.10 by root, Sat Nov 24 06:23:27 2007 UTC

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127.\} 127.\}
128.rm #[ #] #H #V #F C 128.rm #[ #] #H #V #F C
129.\" ======================================================================== 129.\" ========================================================================
130.\" 130.\"
131.IX Title ""<STANDARD INPUT>" 1" 131.IX Title ""<STANDARD INPUT>" 1"
132.TH "<STANDARD INPUT>" 1 "2007-11-23" "perl v5.8.8" "User Contributed Perl Documentation" 132.TH "<STANDARD INPUT>" 1 "2007-11-24" "perl v5.8.8" "User Contributed Perl Documentation"
133.SH "NAME" 133.SH "NAME"
134libev \- a high performance full\-featured event loop written in C 134libev \- a high performance full\-featured event loop written in C
135.SH "SYNOPSIS" 135.SH "SYNOPSIS"
136.IX Header "SYNOPSIS" 136.IX Header "SYNOPSIS"
137.Vb 1 137.Vb 1
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231recommended for this platform. This set is often smaller than the one 231recommended for this platform. This set is often smaller than the one
232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on 232returned by \f(CW\*(C`ev_supported_backends\*(C'\fR, as for example kqueue is broken on
233most BSDs and will not be autodetected unless you explicitly request it 233most BSDs and will not be autodetected unless you explicitly request it
234(assuming you know what you are doing). This is the set of backends that 234(assuming you know what you are doing). This is the set of backends that
235libev will probe for if you specify no backends explicitly. 235libev will probe for if you specify no backends explicitly.
236.IP "unsigned int ev_embeddable_backends ()" 4
237.IX Item "unsigned int ev_embeddable_backends ()"
238Returns the set of backends that are embeddable in other event loops. This
239is the theoretical, all\-platform, value. To find which backends
240might be supported on the current system, you would need to look at
241\&\f(CW\*(C`ev_embeddable_backends () & ev_supported_backends ()\*(C'\fR, likewise for
242recommended ones.
243.Sp
244See the description of \f(CW\*(C`ev_embed\*(C'\fR watchers for more info.
236.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4 245.IP "ev_set_allocator (void *(*cb)(void *ptr, long size))" 4
237.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))" 246.IX Item "ev_set_allocator (void *(*cb)(void *ptr, long size))"
238Sets the allocation function to use (the prototype is similar to the 247Sets the allocation function to use (the prototype is similar to the
239realloc C function, the semantics are identical). It is used to allocate 248realloc C function, the semantics are identical). It is used to allocate
240and free memory (no surprises here). If it returns zero when memory 249and free memory (no surprises here). If it returns zero when memory
… …
1159.IX Subsection "ev_prepare and ev_check - customise your event loop" 1168.IX Subsection "ev_prepare and ev_check - customise your event loop"
1160Prepare and check watchers are usually (but not always) used in tandem: 1169Prepare and check watchers are usually (but not always) used in tandem:
1161prepare watchers get invoked before the process blocks and check watchers 1170prepare watchers get invoked before the process blocks and check watchers
1162afterwards. 1171afterwards.
1163.PP 1172.PP
1164Their main purpose is to integrate other event mechanisms into libev. This 1173Their main purpose is to integrate other event mechanisms into libev and
1165could be used, for example, to track variable changes, implement your own 1174their use is somewhat advanced. This could be used, for example, to track
1166watchers, integrate net-snmp or a coroutine library and lots more. 1175variable changes, implement your own watchers, integrate net-snmp or a
1176coroutine library and lots more.
1167.PP 1177.PP
1168This is done by examining in each prepare call which file descriptors need 1178This is done by examining in each prepare call which file descriptors need
1169to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for 1179to be watched by the other library, registering \f(CW\*(C`ev_io\*(C'\fR watchers for
1170them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries 1180them and starting an \f(CW\*(C`ev_timer\*(C'\fR watcher for any timeouts (many libraries
1171provide just this functionality). Then, in the check watcher you check for 1181provide just this functionality). Then, in the check watcher you check for
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1191Initialises and configures the prepare or check watcher \- they have no 1201Initialises and configures the prepare or check watcher \- they have no
1192parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR 1202parameters of any kind. There are \f(CW\*(C`ev_prepare_set\*(C'\fR and \f(CW\*(C`ev_check_set\*(C'\fR
1193macros, but using them is utterly, utterly and completely pointless. 1203macros, but using them is utterly, utterly and completely pointless.
1194.PP 1204.PP
1195Example: *TODO*. 1205Example: *TODO*.
1206.ie n .Sh """ev_embed"" \- when one backend isn't enough"
1207.el .Sh "\f(CWev_embed\fP \- when one backend isn't enough"
1208.IX Subsection "ev_embed - when one backend isn't enough"
1209This is a rather advanced watcher type that lets you embed one event loop
1210into another.
1211.PP
1212There are primarily two reasons you would want that: work around bugs and
1213prioritise I/O.
1214.PP
1215As an example for a bug workaround, the kqueue backend might only support
1216sockets on some platform, so it is unusable as generic backend, but you
1217still want to make use of it because you have many sockets and it scales
1218so nicely. In this case, you would create a kqueue-based loop and embed it
1219into your default loop (which might use e.g. poll). Overall operation will
1220be a bit slower because first libev has to poll and then call kevent, but
1221at least you can use both at what they are best.
1222.PP
1223As for prioritising I/O: rarely you have the case where some fds have
1224to be watched and handled very quickly (with low latency), and even
1225priorities and idle watchers might have too much overhead. In this case
1226you would put all the high priority stuff in one loop and all the rest in
1227a second one, and embed the second one in the first.
1228.PP
1229As long as the watcher is started it will automatically handle events. The
1230callback will be invoked whenever some events have been handled. You can
1231set the callback to \f(CW0\fR to avoid having to specify one if you are not
1232interested in that.
1233.PP
1234Also, there have not currently been made special provisions for forking:
1235when you fork, you not only have to call \f(CW\*(C`ev_loop_fork\*(C'\fR on both loops,
1236but you will also have to stop and restart any \f(CW\*(C`ev_embed\*(C'\fR watchers
1237yourself.
1238.PP
1239Unfortunately, not all backends are embeddable, only the ones returned by
1240\&\f(CW\*(C`ev_embeddable_backends\*(C'\fR are, which, unfortunately, does not include any
1241portable one.
1242.PP
1243So when you want to use this feature you will always have to be prepared
1244that you cannot get an embeddable loop. The recommended way to get around
1245this is to have a separate variables for your embeddable loop, try to
1246create it, and if that fails, use the normal loop for everything:
1247.PP
1248.Vb 3
1249\& struct ev_loop *loop_hi = ev_default_init (0);
1250\& struct ev_loop *loop_lo = 0;
1251\& struct ev_embed embed;
1252.Ve
1253.PP
1254.Vb 5
1255\& // see if there is a chance of getting one that works
1256\& // (remember that a flags value of 0 means autodetection)
1257\& loop_lo = ev_embeddable_backends () & ev_recommended_backends ()
1258\& ? ev_loop_new (ev_embeddable_backends () & ev_recommended_backends ())
1259\& : 0;
1260.Ve
1261.PP
1262.Vb 8
1263\& // if we got one, then embed it, otherwise default to loop_hi
1264\& if (loop_lo)
1265\& {
1266\& ev_embed_init (&embed, 0, loop_lo);
1267\& ev_embed_start (loop_hi, &embed);
1268\& }
1269\& else
1270\& loop_lo = loop_hi;
1271.Ve
1272.IP "ev_embed_init (ev_embed *, callback, struct ev_loop *loop)" 4
1273.IX Item "ev_embed_init (ev_embed *, callback, struct ev_loop *loop)"
1274.PD 0
1275.IP "ev_embed_set (ev_embed *, callback, struct ev_loop *loop)" 4
1276.IX Item "ev_embed_set (ev_embed *, callback, struct ev_loop *loop)"
1277.PD
1278Configures the watcher to embed the given loop, which must be embeddable.
1196.SH "OTHER FUNCTIONS" 1279.SH "OTHER FUNCTIONS"
1197.IX Header "OTHER FUNCTIONS" 1280.IX Header "OTHER FUNCTIONS"
1198There are some other functions of possible interest. Described. Here. Now. 1281There are some other functions of possible interest. Described. Here. Now.
1199.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4 1282.IP "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 4
1200.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)" 1283.IX Item "ev_once (loop, int fd, int events, ev_tstamp timeout, callback)"

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