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47 47
48 return 0; 48 return 0;
49 } 49 }
50 50
51=head1 DESCRIPTION 51=head1 DESCRIPTION
52
53The newest version of this document is also available as a html-formatted
54web page you might find easier to navigate when reading it for the first
55time: L<http://cvs.schmorp.de/libev/ev.html>.
52 56
53Libev is an event loop: you register interest in certain events (such as a 57Libev is an event loop: you register interest in certain events (such as a
54file descriptor being readable or a timeout occuring), and it will manage 58file descriptor being readable or a timeout occuring), and it will manage
55these event sources and provide your program with events. 59these event sources and provide your program with events.
56 60
482libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is 486libev watchers. However, a pair of C<ev_prepare>/C<ev_check> watchers is
483usually a better approach for this kind of thing. 487usually a better approach for this kind of thing.
484 488
485Here are the gory details of what C<ev_loop> does: 489Here are the gory details of what C<ev_loop> does:
486 490
491 - Before the first iteration, call any pending watchers.
487 * If there are no active watchers (reference count is zero), return. 492 * If there are no active watchers (reference count is zero), return.
488 - Queue prepare watchers and then call all outstanding watchers. 493 - Queue all prepare watchers and then call all outstanding watchers.
489 - If we have been forked, recreate the kernel state. 494 - If we have been forked, recreate the kernel state.
490 - Update the kernel state with all outstanding changes. 495 - Update the kernel state with all outstanding changes.
491 - Update the "event loop time". 496 - Update the "event loop time".
492 - Calculate for how long to block. 497 - Calculate for how long to block.
493 - Block the process, waiting for any events. 498 - Block the process, waiting for any events.
732=item bool ev_is_pending (ev_TYPE *watcher) 737=item bool ev_is_pending (ev_TYPE *watcher)
733 738
734Returns a true value iff the watcher is pending, (i.e. it has outstanding 739Returns a true value iff the watcher is pending, (i.e. it has outstanding
735events but its callback has not yet been invoked). As long as a watcher 740events but its callback has not yet been invoked). As long as a watcher
736is pending (but not active) you must not call an init function on it (but 741is pending (but not active) you must not call an init function on it (but
737C<ev_TYPE_set> is safe) and you must make sure the watcher is available to 742C<ev_TYPE_set> is safe), you must not change its priority, and you must
738libev (e.g. you cnanot C<free ()> it). 743make sure the watcher is available to libev (e.g. you cannot C<free ()>
744it).
739 745
740=item callback ev_cb (ev_TYPE *watcher) 746=item callback ev_cb (ev_TYPE *watcher)
741 747
742Returns the callback currently set on the watcher. 748Returns the callback currently set on the watcher.
743 749
762watchers on the same event and make sure one is called first. 768watchers on the same event and make sure one is called first.
763 769
764If you need to suppress invocation when higher priority events are pending 770If you need to suppress invocation when higher priority events are pending
765you need to look at C<ev_idle> watchers, which provide this functionality. 771you need to look at C<ev_idle> watchers, which provide this functionality.
766 772
773You I<must not> change the priority of a watcher as long as it is active or
774pending.
775
767The default priority used by watchers when no priority has been set is 776The default priority used by watchers when no priority has been set is
768always C<0>, which is supposed to not be too high and not be too low :). 777always C<0>, which is supposed to not be too high and not be too low :).
769 778
770Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is 779Setting a priority outside the range of C<EV_MINPRI> to C<EV_MAXPRI> is
771fine, as long as you do not mind that the priority value you query might 780fine, as long as you do not mind that the priority value you query might
772or might not have been adjusted to be within valid range. 781or might not have been adjusted to be within valid range.
782
783=item ev_invoke (loop, ev_TYPE *watcher, int revents)
784
785Invoke the C<watcher> with the given C<loop> and C<revents>. Neither
786C<loop> nor C<revents> need to be valid as long as the watcher callback
787can deal with that fact.
788
789=item int ev_clear_pending (loop, ev_TYPE *watcher)
790
791If the watcher is pending, this function returns clears its pending status
792and returns its C<revents> bitset (as if its callback was invoked). If the
793watcher isn't pending it does nothing and returns C<0>.
773 794
774=back 795=back
775 796
776 797
777=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER 798=head2 ASSOCIATING CUSTOM DATA WITH A WATCHER
1461with priority higher than or equal to the event loop and one coroutine 1482with priority higher than or equal to the event loop and one coroutine
1462of lower priority, but only once, using idle watchers to keep the event 1483of lower priority, but only once, using idle watchers to keep the event
1463loop from blocking if lower-priority coroutines are active, thus mapping 1484loop from blocking if lower-priority coroutines are active, thus mapping
1464low-priority coroutines to idle/background tasks). 1485low-priority coroutines to idle/background tasks).
1465 1486
1487It is recommended to give C<ev_check> watchers highest (C<EV_MAXPRI>)
1488priority, to ensure that they are being run before any other watchers
1489after the poll. Also, C<ev_check> watchers (and C<ev_prepare> watchers,
1490too) should not activate ("feed") events into libev. While libev fully
1491supports this, they will be called before other C<ev_check> watchers did
1492their job. As C<ev_check> watchers are often used to embed other event
1493loops those other event loops might be in an unusable state until their
1494C<ev_check> watcher ran (always remind yourself to coexist peacefully with
1495others).
1496
1466=over 4 1497=over 4
1467 1498
1468=item ev_prepare_init (ev_prepare *, callback) 1499=item ev_prepare_init (ev_prepare *, callback)
1469 1500
1470=item ev_check_init (ev_check *, callback) 1501=item ev_check_init (ev_check *, callback)
1473parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set> 1504parameters of any kind. There are C<ev_prepare_set> and C<ev_check_set>
1474macros, but using them is utterly, utterly and completely pointless. 1505macros, but using them is utterly, utterly and completely pointless.
1475 1506
1476=back 1507=back
1477 1508
1478Example: To include a library such as adns, you would add IO watchers 1509There are a number of principal ways to embed other event loops or modules
1479and a timeout watcher in a prepare handler, as required by libadns, and 1510into libev. Here are some ideas on how to include libadns into libev
1511(there is a Perl module named C<EV::ADNS> that does this, which you could
1512use for an actually working example. Another Perl module named C<EV::Glib>
1513embeds a Glib main context into libev, and finally, C<Glib::EV> embeds EV
1514into the Glib event loop).
1515
1516Method 1: Add IO watchers and a timeout watcher in a prepare handler,
1480in a check watcher, destroy them and call into libadns. What follows is 1517and in a check watcher, destroy them and call into libadns. What follows
1481pseudo-code only of course: 1518is pseudo-code only of course. This requires you to either use a low
1519priority for the check watcher or use C<ev_clear_pending> explicitly, as
1520the callbacks for the IO/timeout watchers might not have been called yet.
1482 1521
1483 static ev_io iow [nfd]; 1522 static ev_io iow [nfd];
1484 static ev_timer tw; 1523 static ev_timer tw;
1485 1524
1486 static void 1525 static void
1487 io_cb (ev_loop *loop, ev_io *w, int revents) 1526 io_cb (ev_loop *loop, ev_io *w, int revents)
1488 { 1527 {
1489 // set the relevant poll flags
1490 // could also call adns_processreadable etc. here
1491 struct pollfd *fd = (struct pollfd *)w->data;
1492 if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1493 if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1494 } 1528 }
1495 1529
1496 // create io watchers for each fd and a timer before blocking 1530 // create io watchers for each fd and a timer before blocking
1497 static void 1531 static void
1498 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents) 1532 adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
1504 1538
1505 /* the callback is illegal, but won't be called as we stop during check */ 1539 /* the callback is illegal, but won't be called as we stop during check */
1506 ev_timer_init (&tw, 0, timeout * 1e-3); 1540 ev_timer_init (&tw, 0, timeout * 1e-3);
1507 ev_timer_start (loop, &tw); 1541 ev_timer_start (loop, &tw);
1508 1542
1509 // create on ev_io per pollfd 1543 // create one ev_io per pollfd
1510 for (int i = 0; i < nfd; ++i) 1544 for (int i = 0; i < nfd; ++i)
1511 { 1545 {
1512 ev_io_init (iow + i, io_cb, fds [i].fd, 1546 ev_io_init (iow + i, io_cb, fds [i].fd,
1513 ((fds [i].events & POLLIN ? EV_READ : 0) 1547 ((fds [i].events & POLLIN ? EV_READ : 0)
1514 | (fds [i].events & POLLOUT ? EV_WRITE : 0))); 1548 | (fds [i].events & POLLOUT ? EV_WRITE : 0)));
1515 1549
1516 fds [i].revents = 0; 1550 fds [i].revents = 0;
1517 iow [i].data = fds + i;
1518 ev_io_start (loop, iow + i); 1551 ev_io_start (loop, iow + i);
1519 } 1552 }
1520 } 1553 }
1521 1554
1522 // stop all watchers after blocking 1555 // stop all watchers after blocking
1524 adns_check_cb (ev_loop *loop, ev_check *w, int revents) 1557 adns_check_cb (ev_loop *loop, ev_check *w, int revents)
1525 { 1558 {
1526 ev_timer_stop (loop, &tw); 1559 ev_timer_stop (loop, &tw);
1527 1560
1528 for (int i = 0; i < nfd; ++i) 1561 for (int i = 0; i < nfd; ++i)
1562 {
1563 // set the relevant poll flags
1564 // could also call adns_processreadable etc. here
1565 struct pollfd *fd = fds + i;
1566 int revents = ev_clear_pending (iow + i);
1567 if (revents & EV_READ ) fd->revents |= fd->events & POLLIN;
1568 if (revents & EV_WRITE) fd->revents |= fd->events & POLLOUT;
1569
1570 // now stop the watcher
1529 ev_io_stop (loop, iow + i); 1571 ev_io_stop (loop, iow + i);
1572 }
1530 1573
1531 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop)); 1574 adns_afterpoll (adns, fds, nfd, timeval_from (ev_now (loop));
1575 }
1576
1577Method 2: This would be just like method 1, but you run C<adns_afterpoll>
1578in the prepare watcher and would dispose of the check watcher.
1579
1580Method 3: If the module to be embedded supports explicit event
1581notification (adns does), you can also make use of the actual watcher
1582callbacks, and only destroy/create the watchers in the prepare watcher.
1583
1584 static void
1585 timer_cb (EV_P_ ev_timer *w, int revents)
1586 {
1587 adns_state ads = (adns_state)w->data;
1588 update_now (EV_A);
1589
1590 adns_processtimeouts (ads, &tv_now);
1591 }
1592
1593 static void
1594 io_cb (EV_P_ ev_io *w, int revents)
1595 {
1596 adns_state ads = (adns_state)w->data;
1597 update_now (EV_A);
1598
1599 if (revents & EV_READ ) adns_processreadable (ads, w->fd, &tv_now);
1600 if (revents & EV_WRITE) adns_processwriteable (ads, w->fd, &tv_now);
1601 }
1602
1603 // do not ever call adns_afterpoll
1604
1605Method 4: Do not use a prepare or check watcher because the module you
1606want to embed is too inflexible to support it. Instead, youc na override
1607their poll function. The drawback with this solution is that the main
1608loop is now no longer controllable by EV. The C<Glib::EV> module does
1609this.
1610
1611 static gint
1612 event_poll_func (GPollFD *fds, guint nfds, gint timeout)
1613 {
1614 int got_events = 0;
1615
1616 for (n = 0; n < nfds; ++n)
1617 // create/start io watcher that sets the relevant bits in fds[n] and increment got_events
1618
1619 if (timeout >= 0)
1620 // create/start timer
1621
1622 // poll
1623 ev_loop (EV_A_ 0);
1624
1625 // stop timer again
1626 if (timeout >= 0)
1627 ev_timer_stop (EV_A_ &to);
1628
1629 // stop io watchers again - their callbacks should have set
1630 for (n = 0; n < nfds; ++n)
1631 ev_io_stop (EV_A_ iow [n]);
1632
1633 return got_events;
1532 } 1634 }
1533 1635
1534 1636
1535=head2 C<ev_embed> - when one backend isn't enough... 1637=head2 C<ev_embed> - when one backend isn't enough...
1536 1638
1740 1842
1741To use it, 1843To use it,
1742 1844
1743 #include <ev++.h> 1845 #include <ev++.h>
1744 1846
1745(it is not installed by default). This automatically includes F<ev.h> 1847This automatically includes F<ev.h> and puts all of its definitions (many
1746and puts all of its definitions (many of them macros) into the global 1848of them macros) into the global namespace. All C++ specific things are
1747namespace. All C++ specific things are put into the C<ev> namespace. 1849put into the C<ev> namespace. It should support all the same embedding
1850options as F<ev.h>, most notably C<EV_MULTIPLICITY>.
1748 1851
1749It should support all the same embedding options as F<ev.h>, most notably 1852Care has been taken to keep the overhead low. The only data member the C++
1750C<EV_MULTIPLICITY>. 1853classes add (compared to plain C-style watchers) is the event loop pointer
1854that the watcher is associated with (or no additional members at all if
1855you disable C<EV_MULTIPLICITY> when embedding libev).
1856
1857Currently, functions, and static and non-static member functions can be
1858used as callbacks. Other types should be easy to add as long as they only
1859need one additional pointer for context. If you need support for other
1860types of functors please contact the author (preferably after implementing
1861it).
1751 1862
1752Here is a list of things available in the C<ev> namespace: 1863Here is a list of things available in the C<ev> namespace:
1753 1864
1754=over 4 1865=over 4
1755 1866
1771 1882
1772All of those classes have these methods: 1883All of those classes have these methods:
1773 1884
1774=over 4 1885=over 4
1775 1886
1776=item ev::TYPE::TYPE (object *, object::method *) 1887=item ev::TYPE::TYPE ()
1777 1888
1778=item ev::TYPE::TYPE (object *, object::method *, struct ev_loop *) 1889=item ev::TYPE::TYPE (struct ev_loop *)
1779 1890
1780=item ev::TYPE::~TYPE 1891=item ev::TYPE::~TYPE
1781 1892
1782The constructor takes a pointer to an object and a method pointer to 1893The constructor (optionally) takes an event loop to associate the watcher
1783the event handler callback to call in this class. The constructor calls 1894with. If it is omitted, it will use C<EV_DEFAULT>.
1784C<ev_init> for you, which means you have to call the C<set> method 1895
1785before starting it. If you do not specify a loop then the constructor 1896The constructor calls C<ev_init> for you, which means you have to call the
1786automatically associates the default loop with this watcher. 1897C<set> method before starting it.
1898
1899It will not set a callback, however: You have to call the templated C<set>
1900method to set a callback before you can start the watcher.
1901
1902(The reason why you have to use a method is a limitation in C++ which does
1903not allow explicit template arguments for constructors).
1787 1904
1788The destructor automatically stops the watcher if it is active. 1905The destructor automatically stops the watcher if it is active.
1906
1907=item w->set<class, &class::method> (object *)
1908
1909This method sets the callback method to call. The method has to have a
1910signature of C<void (*)(ev_TYPE &, int)>, it receives the watcher as
1911first argument and the C<revents> as second. The object must be given as
1912parameter and is stored in the C<data> member of the watcher.
1913
1914This method synthesizes efficient thunking code to call your method from
1915the C callback that libev requires. If your compiler can inline your
1916callback (i.e. it is visible to it at the place of the C<set> call and
1917your compiler is good :), then the method will be fully inlined into the
1918thunking function, making it as fast as a direct C callback.
1919
1920Example: simple class declaration and watcher initialisation
1921
1922 struct myclass
1923 {
1924 void io_cb (ev::io &w, int revents) { }
1925 }
1926
1927 myclass obj;
1928 ev::io iow;
1929 iow.set <myclass, &myclass::io_cb> (&obj);
1930
1931=item w->set<function> (void *data = 0)
1932
1933Also sets a callback, but uses a static method or plain function as
1934callback. The optional C<data> argument will be stored in the watcher's
1935C<data> member and is free for you to use.
1936
1937The prototype of the C<function> must be C<void (*)(ev::TYPE &w, int)>.
1938
1939See the method-C<set> above for more details.
1940
1941Example:
1942
1943 static void io_cb (ev::io &w, int revents) { }
1944 iow.set <io_cb> ();
1789 1945
1790=item w->set (struct ev_loop *) 1946=item w->set (struct ev_loop *)
1791 1947
1792Associates a different C<struct ev_loop> with this watcher. You can only 1948Associates a different C<struct ev_loop> with this watcher. You can only
1793do this when the watcher is inactive (and not pending either). 1949do this when the watcher is inactive (and not pending either).
1794 1950
1795=item w->set ([args]) 1951=item w->set ([args])
1796 1952
1797Basically the same as C<ev_TYPE_set>, with the same args. Must be 1953Basically the same as C<ev_TYPE_set>, with the same args. Must be
1798called at least once. Unlike the C counterpart, an active watcher gets 1954called at least once. Unlike the C counterpart, an active watcher gets
1799automatically stopped and restarted. 1955automatically stopped and restarted when reconfiguring it with this
1956method.
1800 1957
1801=item w->start () 1958=item w->start ()
1802 1959
1803Starts the watcher. Note that there is no C<loop> argument as the 1960Starts the watcher. Note that there is no C<loop> argument, as the
1804constructor already takes the loop. 1961constructor already stores the event loop.
1805 1962
1806=item w->stop () 1963=item w->stop ()
1807 1964
1808Stops the watcher if it is active. Again, no C<loop> argument. 1965Stops the watcher if it is active. Again, no C<loop> argument.
1809 1966
1834 1991
1835 myclass (); 1992 myclass ();
1836 } 1993 }
1837 1994
1838 myclass::myclass (int fd) 1995 myclass::myclass (int fd)
1839 : io (this, &myclass::io_cb),
1840 idle (this, &myclass::idle_cb)
1841 { 1996 {
1997 io .set <myclass, &myclass::io_cb > (this);
1998 idle.set <myclass, &myclass::idle_cb> (this);
1999
1842 io.start (fd, ev::READ); 2000 io.start (fd, ev::READ);
1843 } 2001 }
1844 2002
1845 2003
1846=head1 MACRO MAGIC 2004=head1 MACRO MAGIC
2123will have the C<struct ev_loop *> as first argument, and you can create 2281will have the C<struct ev_loop *> as first argument, and you can create
2124additional independent event loops. Otherwise there will be no support 2282additional independent event loops. Otherwise there will be no support
2125for multiple event loops and there is no first event loop pointer 2283for multiple event loops and there is no first event loop pointer
2126argument. Instead, all functions act on the single default loop. 2284argument. Instead, all functions act on the single default loop.
2127 2285
2286=item EV_MINPRI
2287
2288=item EV_MAXPRI
2289
2290The range of allowed priorities. C<EV_MINPRI> must be smaller or equal to
2291C<EV_MAXPRI>, but otherwise there are no non-obvious limitations. You can
2292provide for more priorities by overriding those symbols (usually defined
2293to be C<-2> and C<2>, respectively).
2294
2295When doing priority-based operations, libev usually has to linearly search
2296all the priorities, so having many of them (hundreds) uses a lot of space
2297and time, so using the defaults of five priorities (-2 .. +2) is usually
2298fine.
2299
2300If your embedding app does not need any priorities, defining these both to
2301C<0> will save some memory and cpu.
2302
2128=item EV_PERIODIC_ENABLE 2303=item EV_PERIODIC_ENABLE
2129 2304
2130If undefined or defined to be C<1>, then periodic timers are supported. If 2305If undefined or defined to be C<1>, then periodic timers are supported. If
2131defined to be C<0>, then they are not. Disabling them saves a few kB of 2306defined to be C<0>, then they are not. Disabling them saves a few kB of
2132code. 2307code.
2234 2409
2235In this section the complexities of (many of) the algorithms used inside 2410In this section the complexities of (many of) the algorithms used inside
2236libev will be explained. For complexity discussions about backends see the 2411libev will be explained. For complexity discussions about backends see the
2237documentation for C<ev_default_init>. 2412documentation for C<ev_default_init>.
2238 2413
2414All of the following are about amortised time: If an array needs to be
2415extended, libev needs to realloc and move the whole array, but this
2416happens asymptotically never with higher number of elements, so O(1) might
2417mean it might do a lengthy realloc operation in rare cases, but on average
2418it is much faster and asymptotically approaches constant time.
2419
2239=over 4 2420=over 4
2240 2421
2241=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers) 2422=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers)
2242 2423
2424This means that, when you have a watcher that triggers in one hour and
2425there are 100 watchers that would trigger before that then inserting will
2426have to skip those 100 watchers.
2427
2243=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers) 2428=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
2244 2429
2430That means that for changing a timer costs less than removing/adding them
2431as only the relative motion in the event queue has to be paid for.
2432
2245=item Starting io/check/prepare/idle/signal/child watchers: O(1) 2433=item Starting io/check/prepare/idle/signal/child watchers: O(1)
2246 2434
2435These just add the watcher into an array or at the head of a list.
2247=item Stopping check/prepare/idle watchers: O(1) 2436=item Stopping check/prepare/idle watchers: O(1)
2248 2437
2249=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE)) 2438=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2250 2439
2440These watchers are stored in lists then need to be walked to find the
2441correct watcher to remove. The lists are usually short (you don't usually
2442have many watchers waiting for the same fd or signal).
2443
2251=item Finding the next timer per loop iteration: O(1) 2444=item Finding the next timer per loop iteration: O(1)
2252 2445
2253=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd) 2446=item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
2254 2447
2448A change means an I/O watcher gets started or stopped, which requires
2449libev to recalculate its status (and possibly tell the kernel).
2450
2255=item Activating one watcher: O(1) 2451=item Activating one watcher: O(1)
2256 2452
2453=item Priority handling: O(number_of_priorities)
2454
2455Priorities are implemented by allocating some space for each
2456priority. When doing priority-based operations, libev usually has to
2457linearly search all the priorities.
2458
2257=back 2459=back
2258 2460
2259 2461
2260=head1 AUTHOR 2462=head1 AUTHOR
2261 2463

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