… | |
… | |
174 | =item ev_tstamp ev_time () |
174 | =item ev_tstamp ev_time () |
175 | |
175 | |
176 | Returns the current time as libev would use it. Please note that the |
176 | Returns the current time as libev would use it. Please note that the |
177 | C<ev_now> function is usually faster and also often returns the timestamp |
177 | C<ev_now> function is usually faster and also often returns the timestamp |
178 | you actually want to know. Also interesting is the combination of |
178 | you actually want to know. Also interesting is the combination of |
179 | C<ev_update_now> and C<ev_now>. |
179 | C<ev_now_update> and C<ev_now>. |
180 | |
180 | |
181 | =item ev_sleep (ev_tstamp interval) |
181 | =item ev_sleep (ev_tstamp interval) |
182 | |
182 | |
183 | Sleep for the given interval: The current thread will be blocked |
183 | Sleep for the given interval: The current thread will be blocked |
184 | until either it is interrupted or the given time interval has |
184 | until either it is interrupted or the given time interval has |
… | |
… | |
1771 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1771 | detecting time jumps is hard, and some inaccuracies are unavoidable (the |
1772 | monotonic clock option helps a lot here). |
1772 | monotonic clock option helps a lot here). |
1773 | |
1773 | |
1774 | The callback is guaranteed to be invoked only I<after> its timeout has |
1774 | The callback is guaranteed to be invoked only I<after> its timeout has |
1775 | passed (not I<at>, so on systems with very low-resolution clocks this |
1775 | passed (not I<at>, so on systems with very low-resolution clocks this |
1776 | might introduce a small delay). If multiple timers become ready during the |
1776 | might introduce a small delay, see "the special problem of being too |
|
|
1777 | early", below). If multiple timers become ready during the same loop |
1777 | same loop iteration then the ones with earlier time-out values are invoked |
1778 | iteration then the ones with earlier time-out values are invoked before |
1778 | before ones of the same priority with later time-out values (but this is |
1779 | ones of the same priority with later time-out values (but this is no |
1779 | no longer true when a callback calls C<ev_run> recursively). |
1780 | longer true when a callback calls C<ev_run> recursively). |
1780 | |
1781 | |
1781 | =head3 Be smart about timeouts |
1782 | =head3 Be smart about timeouts |
1782 | |
1783 | |
1783 | Many real-world problems involve some kind of timeout, usually for error |
1784 | Many real-world problems involve some kind of timeout, usually for error |
1784 | recovery. A typical example is an HTTP request - if the other side hangs, |
1785 | recovery. A typical example is an HTTP request - if the other side hangs, |
… | |
… | |
1951 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1952 | Method #1 is almost always a bad idea, and buys you nothing. Method #4 is |
1952 | rather complicated, but extremely efficient, something that really pays |
1953 | rather complicated, but extremely efficient, something that really pays |
1953 | off after the first million or so of active timers, i.e. it's usually |
1954 | off after the first million or so of active timers, i.e. it's usually |
1954 | overkill :) |
1955 | overkill :) |
1955 | |
1956 | |
|
|
1957 | =head3 The special problem of being too early |
|
|
1958 | |
|
|
1959 | If you ask a timer to call your callback after three seconds, then |
|
|
1960 | you expect it to be invoked after three seconds - but of course, this |
|
|
1961 | cannot be guaranteed to infinite precision. Less obviously, it cannot be |
|
|
1962 | guaranteed to any precision by libev - imagine somebody suspending the |
|
|
1963 | process a STOP signal for a few hours for example. |
|
|
1964 | |
|
|
1965 | So, libev tries to invoke your callback as soon as possible I<after> the |
|
|
1966 | delay has occurred, but cannot guarantee this. |
|
|
1967 | |
|
|
1968 | A less obvious failure mode is calling your callback too early: many event |
|
|
1969 | loops compare timestamps with a "elapsed delay >= requested delay", but |
|
|
1970 | this can cause your callback to be invoked much earlier than you would |
|
|
1971 | expect. |
|
|
1972 | |
|
|
1973 | To see why, imagine a system with a clock that only offers full second |
|
|
1974 | resolution (think windows if you can't come up with a broken enough OS |
|
|
1975 | yourself). If you schedule a one-second timer at the time 500.9, then the |
|
|
1976 | event loop will schedule your timeout to elapse at a system time of 500 |
|
|
1977 | (500.9 truncated to the resolution) + 1, or 501. |
|
|
1978 | |
|
|
1979 | If an event library looks at the timeout 0.1s later, it will see "501 >= |
|
|
1980 | 501" and invoke the callback 0.1s after it was started, even though a |
|
|
1981 | one-second delay was requested - this is being "too early", despite best |
|
|
1982 | intentions. |
|
|
1983 | |
|
|
1984 | This is the reason why libev will never invoke the callback if the elapsed |
|
|
1985 | delay equals the requested delay, but only when the elapsed delay is |
|
|
1986 | larger than the requested delay. In the example above, libev would only invoke |
|
|
1987 | the callback at system time 502, or 1.1s after the timer was started. |
|
|
1988 | |
|
|
1989 | So, while libev cannot guarantee that your callback will be invoked |
|
|
1990 | exactly when requested, it I<can> and I<does> guarantee that the requested |
|
|
1991 | delay has actually elapsed, or in other words, it always errs on the "too |
|
|
1992 | late" side of things. |
|
|
1993 | |
1956 | =head3 The special problem of time updates |
1994 | =head3 The special problem of time updates |
1957 | |
1995 | |
1958 | Establishing the current time is a costly operation (it usually takes at |
1996 | Establishing the current time is a costly operation (it usually takes |
1959 | least two system calls): EV therefore updates its idea of the current |
1997 | at least one system call): EV therefore updates its idea of the current |
1960 | time only before and after C<ev_run> collects new events, which causes a |
1998 | time only before and after C<ev_run> collects new events, which causes a |
1961 | growing difference between C<ev_now ()> and C<ev_time ()> when handling |
1999 | growing difference between C<ev_now ()> and C<ev_time ()> when handling |
1962 | lots of events in one iteration. |
2000 | lots of events in one iteration. |
1963 | |
2001 | |
1964 | The relative timeouts are calculated relative to the C<ev_now ()> |
2002 | The relative timeouts are calculated relative to the C<ev_now ()> |
… | |
… | |
1970 | ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
2008 | ev_timer_set (&timer, after + ev_now () - ev_time (), 0.); |
1971 | |
2009 | |
1972 | If the event loop is suspended for a long time, you can also force an |
2010 | If the event loop is suspended for a long time, you can also force an |
1973 | update of the time returned by C<ev_now ()> by calling C<ev_now_update |
2011 | update of the time returned by C<ev_now ()> by calling C<ev_now_update |
1974 | ()>. |
2012 | ()>. |
|
|
2013 | |
|
|
2014 | =head3 The special problem of unsynchronised clocks |
|
|
2015 | |
|
|
2016 | Modern systems have a variety of clocks - libev itself uses the normal |
|
|
2017 | "wall clock" clock and, if available, the monotonic clock (to avoid time |
|
|
2018 | jumps). |
|
|
2019 | |
|
|
2020 | Neither of these clocks is synchronised with each other or any other clock |
|
|
2021 | on the system, so C<ev_time ()> might return a considerably different time |
|
|
2022 | than C<gettimeofday ()> or C<time ()>. On a GNU/Linux system, for example, |
|
|
2023 | a call to C<gettimeofday> might return a second count that is one higher |
|
|
2024 | than a directly following call to C<time>. |
|
|
2025 | |
|
|
2026 | The moral of this is to only compare libev-related timestamps with |
|
|
2027 | C<ev_time ()> and C<ev_now ()>, at least if you want better precision than |
|
|
2028 | a second or so. |
|
|
2029 | |
|
|
2030 | One more problem arises due to this lack of synchronisation: if libev uses |
|
|
2031 | the system monotonic clock and you compare timestamps from C<ev_time> |
|
|
2032 | or C<ev_now> from when you started your timer and when your callback is |
|
|
2033 | invoked, you will find that sometimes the callback is a bit "early". |
|
|
2034 | |
|
|
2035 | This is because C<ev_timer>s work in real time, not wall clock time, so |
|
|
2036 | libev makes sure your callback is not invoked before the delay happened, |
|
|
2037 | I<measured according to the real time>, not the system clock. |
|
|
2038 | |
|
|
2039 | If your timeouts are based on a physical timescale (e.g. "time out this |
|
|
2040 | connection after 100 seconds") then this shouldn't bother you as it is |
|
|
2041 | exactly the right behaviour. |
|
|
2042 | |
|
|
2043 | If you want to compare wall clock/system timestamps to your timers, then |
|
|
2044 | you need to use C<ev_periodic>s, as these are based on the wall clock |
|
|
2045 | time, where your comparisons will always generate correct results. |
1975 | |
2046 | |
1976 | =head3 The special problems of suspended animation |
2047 | =head3 The special problems of suspended animation |
1977 | |
2048 | |
1978 | When you leave the server world it is quite customary to hit machines that |
2049 | When you leave the server world it is quite customary to hit machines that |
1979 | can suspend/hibernate - what happens to the clocks during such a suspend? |
2050 | can suspend/hibernate - what happens to the clocks during such a suspend? |
… | |
… | |
3944 | watchers in the constructor. |
4015 | watchers in the constructor. |
3945 | |
4016 | |
3946 | class myclass |
4017 | class myclass |
3947 | { |
4018 | { |
3948 | ev::io io ; void io_cb (ev::io &w, int revents); |
4019 | ev::io io ; void io_cb (ev::io &w, int revents); |
3949 | ev::io2 io2 ; void io2_cb (ev::io &w, int revents); |
4020 | ev::io io2 ; void io2_cb (ev::io &w, int revents); |
3950 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
4021 | ev::idle idle; void idle_cb (ev::idle &w, int revents); |
3951 | |
4022 | |
3952 | myclass (int fd) |
4023 | myclass (int fd) |
3953 | { |
4024 | { |
3954 | io .set <myclass, &myclass::io_cb > (this); |
4025 | io .set <myclass, &myclass::io_cb > (this); |
… | |
… | |
4005 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
4076 | L<http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hlibev>. |
4006 | |
4077 | |
4007 | =item D |
4078 | =item D |
4008 | |
4079 | |
4009 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
4080 | Leandro Lucarella has written a D language binding (F<ev.d>) for libev, to |
4010 | be found at L<http://proj.llucax.com.ar/wiki/evd>. |
4081 | be found at L<http://www.llucax.com.ar/proj/ev.d/index.html>. |
4011 | |
4082 | |
4012 | =item Ocaml |
4083 | =item Ocaml |
4013 | |
4084 | |
4014 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
4085 | Erkki Seppala has written Ocaml bindings for libev, to be found at |
4015 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
4086 | L<http://modeemi.cs.tut.fi/~flux/software/ocaml-ev/>. |
… | |
… | |
4063 | suitable for use with C<EV_A>. |
4134 | suitable for use with C<EV_A>. |
4064 | |
4135 | |
4065 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
4136 | =item C<EV_DEFAULT>, C<EV_DEFAULT_> |
4066 | |
4137 | |
4067 | Similar to the other two macros, this gives you the value of the default |
4138 | Similar to the other two macros, this gives you the value of the default |
4068 | loop, if multiple loops are supported ("ev loop default"). |
4139 | loop, if multiple loops are supported ("ev loop default"). The default loop |
|
|
4140 | will be initialised if it isn't already initialised. |
|
|
4141 | |
|
|
4142 | For non-multiplicity builds, these macros do nothing, so you always have |
|
|
4143 | to initialise the loop somewhere. |
4069 | |
4144 | |
4070 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
4145 | =item C<EV_DEFAULT_UC>, C<EV_DEFAULT_UC_> |
4071 | |
4146 | |
4072 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
4147 | Usage identical to C<EV_DEFAULT> and C<EV_DEFAULT_>, but requires that the |
4073 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
4148 | default loop has been initialised (C<UC> == unchecked). Their behaviour |
… | |
… | |
4376 | provide your own type that you know is safe for your purposes. It is used |
4451 | provide your own type that you know is safe for your purposes. It is used |
4377 | both for signal handler "locking" as well as for signal and thread safety |
4452 | both for signal handler "locking" as well as for signal and thread safety |
4378 | in C<ev_async> watchers. |
4453 | in C<ev_async> watchers. |
4379 | |
4454 | |
4380 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4455 | In the absence of this define, libev will use C<sig_atomic_t volatile> |
4381 | (from F<signal.h>), which is usually good enough on most platforms. |
4456 | (from F<signal.h>), which is usually good enough on most platforms, |
|
|
4457 | although strictly speaking using a type that also implies a memory fence |
|
|
4458 | is required. |
4382 | |
4459 | |
4383 | =item EV_H (h) |
4460 | =item EV_H (h) |
4384 | |
4461 | |
4385 | The name of the F<ev.h> header file used to include it. The default if |
4462 | The name of the F<ev.h> header file used to include it. The default if |
4386 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
4463 | undefined is C<"ev.h"> in F<event.h>, F<ev.c> and F<ev++.h>. This can be |
… | |
… | |
4409 | If undefined or defined to C<1>, then all event-loop-specific functions |
4486 | If undefined or defined to C<1>, then all event-loop-specific functions |
4410 | will have the C<struct ev_loop *> as first argument, and you can create |
4487 | will have the C<struct ev_loop *> as first argument, and you can create |
4411 | additional independent event loops. Otherwise there will be no support |
4488 | additional independent event loops. Otherwise there will be no support |
4412 | for multiple event loops and there is no first event loop pointer |
4489 | for multiple event loops and there is no first event loop pointer |
4413 | argument. Instead, all functions act on the single default loop. |
4490 | argument. Instead, all functions act on the single default loop. |
|
|
4491 | |
|
|
4492 | Note that C<EV_DEFAULT> and C<EV_DEFAULT_> will no longer provide a |
|
|
4493 | default loop when multiplicity is switched off - you always have to |
|
|
4494 | initialise the loop manually in this case. |
4414 | |
4495 | |
4415 | =item EV_MINPRI |
4496 | =item EV_MINPRI |
4416 | |
4497 | |
4417 | =item EV_MAXPRI |
4498 | =item EV_MAXPRI |
4418 | |
4499 | |
… | |
… | |
5048 | |
5129 | |
5049 | The type C<double> is used to represent timestamps. It is required to |
5130 | The type C<double> is used to represent timestamps. It is required to |
5050 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
5131 | have at least 51 bits of mantissa (and 9 bits of exponent), which is |
5051 | good enough for at least into the year 4000 with millisecond accuracy |
5132 | good enough for at least into the year 4000 with millisecond accuracy |
5052 | (the design goal for libev). This requirement is overfulfilled by |
5133 | (the design goal for libev). This requirement is overfulfilled by |
5053 | implementations using IEEE 754, which is basically all existing ones. With |
5134 | implementations using IEEE 754, which is basically all existing ones. |
|
|
5135 | |
5054 | IEEE 754 doubles, you get microsecond accuracy until at least 2200. |
5136 | With IEEE 754 doubles, you get microsecond accuracy until at least the |
|
|
5137 | year 2255 (and millisecond accuracy till the year 287396 - by then, libev |
|
|
5138 | is either obsolete or somebody patched it to use C<long double> or |
|
|
5139 | something like that, just kidding). |
5055 | |
5140 | |
5056 | =back |
5141 | =back |
5057 | |
5142 | |
5058 | If you know of other additional requirements drop me a note. |
5143 | If you know of other additional requirements drop me a note. |
5059 | |
5144 | |