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Comparing libev/ev.pod (file contents):
Revision 1.126 by root, Fri Feb 1 13:46:26 2008 UTC vs.
Revision 1.130 by root, Wed Feb 6 18:34:24 2008 UTC

… …
2078is that the author does not know of a simple (or any) algorithm for a 2078is that the author does not know of a simple (or any) algorithm for a
2079multiple-writer-single-reader queue that works in all cases and doesn't 2079multiple-writer-single-reader queue that works in all cases and doesn't
2080need elaborate support such as pthreads. 2080need elaborate support such as pthreads.
2081 2081
2082That means that if you want to queue data, you have to provide your own 2082That means that if you want to queue data, you have to provide your own
2083queue. And here is how you would implement locking: 2083queue. But at least I can tell you would implement locking around your
2084queue:
2084 2085
2085=over 4 2086=over 4
2086 2087
2087=item queueing from a signal handler context 2088=item queueing from a signal handler context
2088 2089
… …
2125 2126
2126=item queueing from a thread context 2127=item queueing from a thread context
2127 2128
2128The strategy for threads is different, as you cannot (easily) block 2129The strategy for threads is different, as you cannot (easily) block
2129threads but you can easily preempt them, so to queue safely you need to 2130threads but you can easily preempt them, so to queue safely you need to
2130emply a traditional mutex lock, such as in this pthread example: 2131employ a traditional mutex lock, such as in this pthread example:
2131 2132
2132 static ev_async mysig; 2133 static ev_async mysig;
2133 static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER; 2134 static pthread_mutex_t mymutex = PTHREAD_MUTEX_INITIALIZER;
2134 2135
2135 static void 2136 static void
… …
2697=item EV_ATOMIC_T 2698=item EV_ATOMIC_T
2698 2699
2699Libev requires an integer type (suitable for storing C<0> or C<1>) whose 2700Libev requires an integer type (suitable for storing C<0> or C<1>) whose
2700access is atomic with respect to other threads or signal contexts. No such 2701access is atomic with respect to other threads or signal contexts. No such
2701type is easily found in the C language, so you can provide your own type 2702type is easily found in the C language, so you can provide your own type
2702that you know is safe for your purposes. 2703that you know is safe for your purposes. It is used both for signal handler "locking"
2704as well as for signal and thread safety in C<ev_async> watchers.
2703 2705
2704In the absense of this define, libev will use C<sig_atomic_t volatile> 2706In the absense of this define, libev will use C<sig_atomic_t volatile>
2705(from F<signal.h>), which is usually good enough on most platforms. 2707(from F<signal.h>), which is usually good enough on most platforms.
2706 2708
2707=item EV_H 2709=item EV_H
… …
2911=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers) 2913=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers)
2912 2914
2913That means that changing a timer costs less than removing/adding them 2915That means that changing a timer costs less than removing/adding them
2914as only the relative motion in the event queue has to be paid for. 2916as only the relative motion in the event queue has to be paid for.
2915 2917
2916=item Starting io/check/prepare/idle/signal/child watchers: O(1) 2918=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1)
2917 2919
2918These just add the watcher into an array or at the head of a list. 2920These just add the watcher into an array or at the head of a list.
2919 2921
2920=item Stopping check/prepare/idle watchers: O(1) 2922=item Stopping check/prepare/idle/fork/async watchers: O(1)
2921 2923
2922=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE)) 2924=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))
2923 2925
2924These watchers are stored in lists then need to be walked to find the 2926These watchers are stored in lists then need to be walked to find the
2925correct watcher to remove. The lists are usually short (you don't usually 2927correct watcher to remove. The lists are usually short (you don't usually
… …
2941=item Priority handling: O(number_of_priorities) 2943=item Priority handling: O(number_of_priorities)
2942 2944
2943Priorities are implemented by allocating some space for each 2945Priorities are implemented by allocating some space for each
2944priority. When doing priority-based operations, libev usually has to 2946priority. When doing priority-based operations, libev usually has to
2945linearly search all the priorities, but starting/stopping and activating 2947linearly search all the priorities, but starting/stopping and activating
2946watchers becomes O(1) w.r.t. prioritiy handling. 2948watchers becomes O(1) w.r.t. priority handling.
2949
2950=item Sending an ev_async: O(1)
2951
2952=item Processing ev_async_send: O(number_of_async_watchers)
2953
2954=item Processing signals: O(max_signal_number)
2955
2956Sending involves a syscall I<iff> there were no other C<ev_async_send>
2957calls in the current loop iteration. Checking for async and signal events
2958involves iterating over all running async watchers or all signal numbers.
2947 2959
2948=back 2960=back
2949 2961
2950 2962
2951=head1 Win32 platform limitations and workarounds 2963=head1 Win32 platform limitations and workarounds

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