*** empty log message ***

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index edd3a23ae53492b8e9a92d1cf664202df5c8875a..2269dff05bf943283e66142983eb0ff7c7b2ba2a 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -6,7 +6,7 @@ libev - a high performance full-featured event loop written in C
 
   #include <ev.h>
 
 
   #include <ev.h>
 

-=head1 EXAMPLE PROGRAM
+=head2 EXAMPLE PROGRAM

 
   #include <ev.h>
 
 
   #include <ev.h>
 


@@ -67,7 +67,7 @@ watchers>, which are relatively small C structures you initialise with the
 details of the event, and then hand it over to libev by I<starting> the
 watcher.
 
 details of the event, and then hand it over to libev by I<starting> the
 watcher.
 

-=head1 FEATURES
+=head2 FEATURES

 
 Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
 BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
 
 Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
 BSD-specific C<kqueue> and the Solaris-specific event port mechanisms


@@ -84,7 +84,7 @@ It also is quite fast (see this
 L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
 for example).
 
 L<benchmark|http://libev.schmorp.de/bench.html> comparing it to libevent
 for example).
 

-=head1 CONVENTIONS
+=head2 CONVENTIONS

 
 Libev is very configurable. In this manual the default configuration will
 be described, which supports multiple event loops. For more info about
 
 Libev is very configurable. In this manual the default configuration will
 be described, which supports multiple event loops. For more info about


@@ -93,7 +93,7 @@ this manual. If libev was configured without support for multiple event
 loops, then all functions taking an initial argument of name C<loop>
 (which is always of type C<struct ev_loop *>) will not have this argument.
 
 loops, then all functions taking an initial argument of name C<loop>
 (which is always of type C<struct ev_loop *>) will not have this argument.
 

-=head1 TIME REPRESENTATION
+=head2 TIME REPRESENTATION

 
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near
 
 Libev represents time as a single floating point number, representing the
 (fractional) number of seconds since the (POSIX) epoch (somewhere near


@@ -308,15 +308,24 @@ environment variable.
 This is your standard select(2) backend. Not I<completely> standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 but if that fails, expect a fairly low limit on the number of fds when
 This is your standard select(2) backend. Not I<completely> standard, as
 libev tries to roll its own fd_set with no limits on the number of fds,
 but if that fails, expect a fairly low limit on the number of fds when

-using this backend. It doesn't scale too well (O(highest_fd)), but its usually
-the fastest backend for a low number of fds.
+using this backend. It doesn't scale too well (O(highest_fd)), but its
+usually the fastest backend for a low number of (low-numbered :) fds.
+
+To get good performance out of this backend you need a high amount of
+parallelity (most of the file descriptors should be busy). If you are
+writing a server, you should C<accept ()> in a loop to accept as many
+connections as possible during one iteration. You might also want to have
+a look at C<ev_set_io_collect_interval ()> to increase the amount of
+readyness notifications you get per iteration.

 
 =item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)
 
 
 =item C<EVBACKEND_POLL>    (value 2, poll backend, available everywhere except on windows)
 

-And this is your standard poll(2) backend. It's more complicated than
-select, but handles sparse fds better and has no artificial limit on the
-number of fds you can use (except it will slow down considerably with a
-lot of inactive fds). It scales similarly to select, i.e. O(total_fds).
+And this is your standard poll(2) backend. It's more complicated
+than select, but handles sparse fds better and has no artificial
+limit on the number of fds you can use (except it will slow down
+considerably with a lot of inactive fds). It scales similarly to select,
+i.e. O(total_fds). See the entry for C<EVBACKEND_SELECT>, above, for
+performance tips.

 
 =item C<EVBACKEND_EPOLL>   (value 4, Linux)
 
 
 =item C<EVBACKEND_EPOLL>   (value 4, Linux)
 


@@ -326,7 +335,7 @@ like O(total_fds) where n is the total number of fds (or the highest fd),
 epoll scales either O(1) or O(active_fds). The epoll design has a number
 of shortcomings, such as silently dropping events in some hard-to-detect
 cases and rewiring a syscall per fd change, no fork support and bad
 epoll scales either O(1) or O(active_fds). The epoll design has a number
 of shortcomings, such as silently dropping events in some hard-to-detect
 cases and rewiring a syscall per fd change, no fork support and bad

-support for dup:
+support for dup.

 
 While stopping, setting and starting an I/O watcher in the same iteration
 will result in some caching, there is still a syscall per such incident
 
 While stopping, setting and starting an I/O watcher in the same iteration
 will result in some caching, there is still a syscall per such incident


@@ -338,6 +347,13 @@ Please note that epoll sometimes generates spurious notifications, so you
 need to use non-blocking I/O or other means to avoid blocking when no data
 (or space) is available.
 
 need to use non-blocking I/O or other means to avoid blocking when no data
 (or space) is available.
 

+Best performance from this backend is achieved by not unregistering all
+watchers for a file descriptor until it has been closed, if possible, i.e.
+keep at least one watcher active per fd at all times.
+
+While nominally embeddeble in other event loops, this feature is broken in
+all kernel versions tested so far.
+

 =item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
 
 Kqueue deserves special mention, as at the time of this writing, it
 =item C<EVBACKEND_KQUEUE>  (value 8, most BSD clones)
 
 Kqueue deserves special mention, as at the time of this writing, it


@@ -359,9 +375,21 @@ cause an extra syscall as with C<EVBACKEND_EPOLL>, it still adds up to
 two event changes per incident, support for C<fork ()> is very bad and it
 drops fds silently in similarly hard-to-detect cases.
 
 two event changes per incident, support for C<fork ()> is very bad and it
 drops fds silently in similarly hard-to-detect cases.
 

+This backend usually performs well under most conditions.
+
+While nominally embeddable in other event loops, this doesn't work
+everywhere, so you might need to test for this. And since it is broken
+almost everywhere, you should only use it when you have a lot of sockets
+(for which it usually works), by embedding it into another event loop
+(e.g. C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>) and using it only for
+sockets.
+

 =item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
 
 =item C<EVBACKEND_DEVPOLL> (value 16, Solaris 8)
 

-This is not implemented yet (and might never be).
+This is not implemented yet (and might never be, unless you send me an
+implementation). According to reports, C</dev/poll> only supports sockets
+and is not embeddable, which would limit the usefulness of this backend
+immensely.

 
 =item C<EVBACKEND_PORT>    (value 32, Solaris 10)
 
 
 =item C<EVBACKEND_PORT>    (value 32, Solaris 10)
 


@@ -372,12 +400,19 @@ Please note that solaris event ports can deliver a lot of spurious
 notifications, so you need to use non-blocking I/O or other means to avoid
 blocking when no data (or space) is available.
 
 notifications, so you need to use non-blocking I/O or other means to avoid
 blocking when no data (or space) is available.
 

+While this backend scales well, it requires one system call per active
+file descriptor per loop iteration. For small and medium numbers of file
+descriptors a "slow" C<EVBACKEND_SELECT> or C<EVBACKEND_POLL> backend
+might perform better.
+

 =item C<EVBACKEND_ALL>
 
 Try all backends (even potentially broken ones that wouldn't be tried
 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
 
 =item C<EVBACKEND_ALL>
 
 Try all backends (even potentially broken ones that wouldn't be tried
 with C<EVFLAG_AUTO>). Since this is a mask, you can do stuff such as
 C<EVBACKEND_ALL & ~EVBACKEND_KQUEUE>.
 

+It is definitely not recommended to use this flag.
+

 =back
 
 If one or more of these are ored into the flags value, then only these
 =back
 
 If one or more of these are ored into the flags value, then only these


@@ -601,7 +636,7 @@ overhead for the actual polling but can deliver many events at once.
 By setting a higher I<io collect interval> you allow libev to spend more
 time collecting I/O events, so you can handle more events per iteration,
 at the cost of increasing latency. Timeouts (both C<ev_periodic> and
 By setting a higher I<io collect interval> you allow libev to spend more
 time collecting I/O events, so you can handle more events per iteration,
 at the cost of increasing latency. Timeouts (both C<ev_periodic> and

-C<ev_timer>) will be not affected. Setting this to a non-null bvalue will
+C<ev_timer>) will be not affected. Setting this to a non-null value will

 introduce an additional C<ev_sleep ()> call into most loop iterations.
 
 Likewise, by setting a higher I<timeout collect interval> you allow libev
 introduce an additional C<ev_sleep ()> call into most loop iterations.
 
 Likewise, by setting a higher I<timeout collect interval> you allow libev


@@ -999,12 +1034,12 @@ optimisations to libev.
 =head3 The special problem of dup'ed file descriptors
 
 Some backends (e.g. epoll), cannot register events for file descriptors,
 =head3 The special problem of dup'ed file descriptors
 
 Some backends (e.g. epoll), cannot register events for file descriptors,

-but only events for the underlying file descriptions. That menas when you
+but only events for the underlying file descriptions. That means when you

 have C<dup ()>'ed file descriptors and register events for them, only one
 file descriptor might actually receive events.
 
 have C<dup ()>'ed file descriptors and register events for them, only one
 file descriptor might actually receive events.
 

-There is no workaorund possible except not registering events
-for potentially C<dup ()>'ed file descriptors or to resort to
+There is no workaround possible except not registering events
+for potentially C<dup ()>'ed file descriptors, or to resort to

 C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
 
 =head3 The special problem of fork
 C<EVBACKEND_SELECT> or C<EVBACKEND_POLL>.
 
 =head3 The special problem of fork


@@ -2493,7 +2528,7 @@ increase this value (I<must> be a power of two).
 
 =item EV_INOTIFY_HASHSIZE
 
 
 =item EV_INOTIFY_HASHSIZE
 

-C<ev_staz> watchers use a small hash table to distribute workload by
+C<ev_stat> watchers use a small hash table to distribute workload by

 inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
 usually more than enough. If you need to manage thousands of C<ev_stat>
 watchers you might want to increase this value (I<must> be a power of
 inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>),
 usually more than enough. If you need to manage thousands of C<ev_stat>
 watchers you might want to increase this value (I<must> be a power of


@@ -2599,16 +2634,17 @@ it is much faster and asymptotically approaches constant time.
 
 This means that, when you have a watcher that triggers in one hour and
 there are 100 watchers that would trigger before that then inserting will
 
 This means that, when you have a watcher that triggers in one hour and
 there are 100 watchers that would trigger before that then inserting will

-have to skip those 100 watchers.
+have to skip roughly seven (C<ld 100>) of these watchers.

 
 

-=item Changing timer/periodic watchers (by autorepeat, again): O(log skipped_other_timers)
+=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)

 
 

-That means that for changing a timer costs less than removing/adding them
+That means that changing a timer costs less than removing/adding them

 as only the relative motion in the event queue has to be paid for.
 
 =item Starting io/check/prepare/idle/signal/child watchers: O(1)
 
 These just add the watcher into an array or at the head of a list.
 as only the relative motion in the event queue has to be paid for.
 
 =item Starting io/check/prepare/idle/signal/child watchers: O(1)
 
 These just add the watcher into an array or at the head of a list.

+

 =item Stopping check/prepare/idle watchers: O(1)
 
 =item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
 =item Stopping check/prepare/idle watchers: O(1)
 
 =item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))


@@ -2617,20 +2653,25 @@ These watchers are stored in lists then need to be walked to find the
 correct watcher to remove. The lists are usually short (you don't usually
 have many watchers waiting for the same fd or signal).
 
 correct watcher to remove. The lists are usually short (you don't usually
 have many watchers waiting for the same fd or signal).
 

-=item Finding the next timer per loop iteration: O(1)
+=item Finding the next timer in each loop iteration: O(1)
+
+By virtue of using a binary heap, the next timer is always found at the
+beginning of the storage array.

 
 =item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
 
 A change means an I/O watcher gets started or stopped, which requires
 
 =item Each change on a file descriptor per loop iteration: O(number_of_watchers_for_this_fd)
 
 A change means an I/O watcher gets started or stopped, which requires

-libev to recalculate its status (and possibly tell the kernel).
+libev to recalculate its status (and possibly tell the kernel, depending
+on backend and wether C<ev_io_set> was used).

 
 

-=item Activating one watcher: O(1)
+=item Activating one watcher (putting it into the pending state): O(1)

 
 =item Priority handling: O(number_of_priorities)
 
 Priorities are implemented by allocating some space for each
 priority. When doing priority-based operations, libev usually has to
 
 =item Priority handling: O(number_of_priorities)
 
 Priorities are implemented by allocating some space for each
 priority. When doing priority-based operations, libev usually has to

-linearly search all the priorities.
+linearly search all the priorities, but starting/stopping and activating
+watchers becomes O(1) w.r.t. prioritiy handling.

 
 =back
 
 
 =back