--- libev/ev.pod 2008/05/24 03:08:03 1.161 +++ libev/ev.pod 2008/10/26 00:52:51 1.203 @@ -4,63 +4,63 @@ =head1 SYNOPSIS - #include + #include =head2 EXAMPLE PROGRAM - // a single header file is required - #include + // a single header file is required + #include - // every watcher type has its own typedef'd struct - // with the name ev_ - ev_io stdin_watcher; - ev_timer timeout_watcher; - - // all watcher callbacks have a similar signature - // this callback is called when data is readable on stdin - static void - stdin_cb (EV_P_ struct ev_io *w, int revents) - { - puts ("stdin ready"); - // for one-shot events, one must manually stop the watcher - // with its corresponding stop function. - ev_io_stop (EV_A_ w); - - // this causes all nested ev_loop's to stop iterating - ev_unloop (EV_A_ EVUNLOOP_ALL); - } - - // another callback, this time for a time-out - static void - timeout_cb (EV_P_ struct ev_timer *w, int revents) - { - puts ("timeout"); - // this causes the innermost ev_loop to stop iterating - ev_unloop (EV_A_ EVUNLOOP_ONE); - } - - int - main (void) - { - // use the default event loop unless you have special needs - struct ev_loop *loop = ev_default_loop (0); - - // initialise an io watcher, then start it - // this one will watch for stdin to become readable - ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); - ev_io_start (loop, &stdin_watcher); - - // initialise a timer watcher, then start it - // simple non-repeating 5.5 second timeout - ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); - ev_timer_start (loop, &timeout_watcher); - - // now wait for events to arrive - ev_loop (loop, 0); - - // unloop was called, so exit - return 0; - } + // every watcher type has its own typedef'd struct + // with the name ev_TYPE + ev_io stdin_watcher; + ev_timer timeout_watcher; + + // all watcher callbacks have a similar signature + // this callback is called when data is readable on stdin + static void + stdin_cb (EV_P_ ev_io *w, int revents) + { + puts ("stdin ready"); + // for one-shot events, one must manually stop the watcher + // with its corresponding stop function. + ev_io_stop (EV_A_ w); + + // this causes all nested ev_loop's to stop iterating + ev_unloop (EV_A_ EVUNLOOP_ALL); + } + + // another callback, this time for a time-out + static void + timeout_cb (EV_P_ ev_timer *w, int revents) + { + puts ("timeout"); + // this causes the innermost ev_loop to stop iterating + ev_unloop (EV_A_ EVUNLOOP_ONE); + } + + int + main (void) + { + // use the default event loop unless you have special needs + ev_loop *loop = ev_default_loop (0); + + // initialise an io watcher, then start it + // this one will watch for stdin to become readable + ev_io_init (&stdin_watcher, stdin_cb, /*STDIN_FILENO*/ 0, EV_READ); + ev_io_start (loop, &stdin_watcher); + + // initialise a timer watcher, then start it + // simple non-repeating 5.5 second timeout + ev_timer_init (&timeout_watcher, timeout_cb, 5.5, 0.); + ev_timer_start (loop, &timeout_watcher); + + // now wait for events to arrive + ev_loop (loop, 0); + + // unloop was called, so exit + return 0; + } =head1 DESCRIPTION @@ -105,7 +105,7 @@ more info about various configuration options please have a look at B section in this manual. If libev was configured without support for multiple event loops, then all functions taking an initial argument of -name C (which is always of type C) will not have +name C (which is always of type C) will not have this argument. =head2 TIME REPRESENTATION @@ -180,9 +180,9 @@ Example: Make sure we haven't accidentally been linked against the wrong version. - assert (("libev version mismatch", - ev_version_major () == EV_VERSION_MAJOR - && ev_version_minor () >= EV_VERSION_MINOR)); + assert (("libev version mismatch", + ev_version_major () == EV_VERSION_MAJOR + && ev_version_minor () >= EV_VERSION_MINOR)); =item unsigned int ev_supported_backends () @@ -194,8 +194,8 @@ Example: make sure we have the epoll method, because yeah this is cool and a must have and can we have a torrent of it please!!!11 - assert (("sorry, no epoll, no sex", - ev_supported_backends () & EVBACKEND_EPOLL)); + assert (("sorry, no epoll, no sex", + ev_supported_backends () & EVBACKEND_EPOLL)); =item unsigned int ev_recommended_backends () @@ -216,7 +216,7 @@ See the description of C watchers for more info. -=item ev_set_allocator (void *(*cb)(void *ptr, long size)) +=item ev_set_allocator (void *(*cb)(void *ptr, long size)) [NOT REENTRANT] Sets the allocation function to use (the prototype is similar - the semantics are identical to the C C89/SuS/POSIX function). It is @@ -252,7 +252,7 @@ ... ev_set_allocator (persistent_realloc); -=item ev_set_syserr_cb (void (*cb)(const char *msg)); +=item ev_set_syserr_cb (void (*cb)(const char *msg)); [NOT REENTRANT] Set the callback function to call on a retryable system call error (such as failed select, poll, epoll_wait). The message is a printable string @@ -278,9 +278,13 @@ =head1 FUNCTIONS CONTROLLING THE EVENT LOOP -An event loop is described by a C. The library knows two -types of such loops, the I loop, which supports signals and child -events, and dynamically created loops which do not. +An event loop is described by a C (the C +is I optional in this case, as there is also an C +I). + +The library knows two types of such loops, the I loop, which +supports signals and child events, and dynamically created loops which do +not. =over 4 @@ -361,6 +365,10 @@ a look at C to increase the amount of readiness notifications you get per iteration. +This backend maps C to the C set and C to the +C set (and to work around Microsoft Windows bugs, also onto the +C set on that platform). + =item C (value 2, poll backend, available everywhere except on windows) And this is your standard poll(2) backend. It's more complicated @@ -370,6 +378,9 @@ i.e. O(total_fds). See the entry for C, above, for performance tips. +This backend maps C to C, and +C to C. + =item C (value 4, Linux) For few fds, this backend is a bit little slower than poll and select, @@ -391,21 +402,25 @@ (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. +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. Stopping and +starting a watcher (without re-setting it) also usually doesn't cause +extra overhead. While nominally embeddable in other event loops, this feature is broken in all kernel versions tested so far. +This backend maps C and C in the same way as +C. + =item C (value 8, most BSD clones) -Kqueue deserves special mention, as at the time of this writing, it -was broken on all BSDs except NetBSD (usually it doesn't work reliably -with anything but sockets and pipes, except on Darwin, where of course -it's completely useless). For this reason it's not being "auto-detected" -unless you explicitly specify it explicitly in the flags (i.e. using -C) or libev was compiled on a known-to-be-good (-enough) -system like NetBSD. +Kqueue deserves special mention, as at the time of this writing, it was +broken on all BSDs except NetBSD (usually it doesn't work reliably with +anything but sockets and pipes, except on Darwin, where of course it's +completely useless). For this reason it's not being "auto-detected" unless +you explicitly specify it in the flags (i.e. using C) or +libev was compiled on a known-to-be-good (-enough) system like NetBSD. You still can embed kqueue into a normal poll or select backend and use it only for sockets (after having made sure that sockets work with kqueue on @@ -415,7 +430,7 @@ kernel is more efficient (which says nothing about its actual speed, of course). While stopping, setting and starting an I/O watcher does never cause an extra system call as with C, it still adds up to -two event changes per incident, support for C is very bad and it +two event changes per incident. Support for C is very bad and it drops fds silently in similarly hard-to-detect cases. This backend usually performs well under most conditions. @@ -424,8 +439,12 @@ 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 or C) and using it only for -sockets. +(e.g. C or C) and, did I mention it, +using it only for sockets. + +This backend maps C into an C kevent with +C, and C into an C kevent with +C. =item C (value 16, Solaris 8) @@ -448,9 +467,13 @@ descriptors a "slow" C or C backend might perform better. -On the positive side, ignoring the spurious readiness notifications, this -backend actually performed to specification in all tests and is fully -embeddable, which is a rare feat among the OS-specific backends. +On the positive side, with the exception of the spurious readiness +notifications, this backend actually performed fully to specification +in all tests and is fully embeddable, which is a rare feat among the +OS-specific backends. + +This backend maps C and C in the same way as +C. =item C @@ -466,21 +489,22 @@ backends will be tried (in the reverse order as listed here). If none are specified, all backends in C will be tried. -The most typical usage is like this: +Example: This is the most typical usage. - if (!ev_default_loop (0)) - fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); + if (!ev_default_loop (0)) + fatal ("could not initialise libev, bad $LIBEV_FLAGS in environment?"); -Restrict libev to the select and poll backends, and do not allow +Example: Restrict libev to the select and poll backends, and do not allow environment settings to be taken into account: - ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); + ev_default_loop (EVBACKEND_POLL | EVBACKEND_SELECT | EVFLAG_NOENV); -Use whatever libev has to offer, but make sure that kqueue is used if -available (warning, breaks stuff, best use only with your own private -event loop and only if you know the OS supports your types of fds): +Example: Use whatever libev has to offer, but make sure that kqueue is +used if available (warning, breaks stuff, best use only with your own +private event loop and only if you know the OS supports your types of +fds): - ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); + ev_default_loop (ev_recommended_backends () | EVBACKEND_KQUEUE); =item struct ev_loop *ev_loop_new (unsigned int flags) @@ -495,9 +519,9 @@ Example: Try to create a event loop that uses epoll and nothing else. - struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); - if (!epoller) - fatal ("no epoll found here, maybe it hides under your chair"); + struct ev_loop *epoller = ev_loop_new (EVBACKEND_EPOLL | EVFLAG_NOENV); + if (!epoller) + fatal ("no epoll found here, maybe it hides under your chair"); =item ev_default_destroy () @@ -509,9 +533,9 @@ the easiest thing, you can just ignore the watchers and/or C them for example). -Note that certain global state, such as signal state, will not be freed by -this function, and related watchers (such as signal and child watchers) -would need to be stopped manually. +Note that certain global state, such as signal state (and installed signal +handlers), will not be freed by this function, and related watchers (such +as signal and child watchers) would need to be stopped manually. In general it is not advisable to call this function except in the rare occasion where you really need to free e.g. the signal handling @@ -546,11 +570,13 @@ Like C, but acts on an event loop created by C. Yes, you have to call this on every allocated event loop -after fork, and how you do this is entirely your own problem. +after fork that you want to re-use in the child, and how you do this is +entirely your own problem. =item int ev_is_default_loop (loop) -Returns true when the given loop actually is the default loop, false otherwise. +Returns true when the given loop is, in fact, the default loop, and false +otherwise. =item unsigned int ev_loop_count (loop) @@ -575,6 +601,18 @@ time used for relative timers. You can treat it as the timestamp of the event occurring (or more correctly, libev finding out about it). +=item ev_now_update (loop) + +Establishes the current time by querying the kernel, updating the time +returned by C in the progress. This is a costly operation and +is usually done automatically within C. + +This function is rarely useful, but when some event callback runs for a +very long time without entering the event loop, updating libev's idea of +the current time is a good idea. + +See also "The special problem of time updates" in the C section. + =item ev_loop (loop, int flags) Finally, this is it, the event handler. This function usually is called @@ -586,41 +624,48 @@ Please note that an explicit C is usually better than relying on all watchers to be stopped when deciding when a program has -finished (especially in interactive programs), but having a program that -automatically loops as long as it has to and no longer by virtue of -relying on its watchers stopping correctly is a thing of beauty. +finished (especially in interactive programs), but having a program +that automatically loops as long as it has to and no longer by virtue +of relying on its watchers stopping correctly, that is truly a thing of +beauty. A flags value of C will look for new events, will handle -those events and any outstanding ones, but will not block your process in -case there are no events and will return after one iteration of the loop. +those events and any already outstanding ones, but will not block your +process in case there are no events and will return after one iteration of +the loop. A flags value of C will look for new events (waiting if -necessary) and will handle those and any outstanding ones. It will block -your process until at least one new event arrives, and will return after -one iteration of the loop. This is useful if you are waiting for some -external event in conjunction with something not expressible using other -libev watchers. However, a pair of C/C watchers is +necessary) and will handle those and any already outstanding ones. It +will block your process until at least one new event arrives (which could +be an event internal to libev itself, so there is no guarentee that a +user-registered callback will be called), and will return after one +iteration of the loop. + +This is useful if you are waiting for some external event in conjunction +with something not expressible using other libev watchers (i.e. "roll your +own C"). However, a pair of C/C watchers is usually a better approach for this kind of thing. Here are the gory details of what C does: - Before the first iteration, call any pending watchers. * If EVFLAG_FORKCHECK was used, check for a fork. - - If a fork was detected, queue and call all fork watchers. + - If a fork was detected (by any means), queue and call all fork watchers. - Queue and call all prepare watchers. - - If we have been forked, recreate the kernel state. + - If we have been forked, detach and recreate the kernel state + as to not disturb the other process. - Update the kernel state with all outstanding changes. - - Update the "event loop time". + - Update the "event loop time" (ev_now ()). - Calculate for how long to sleep or block, if at all (active idle watchers, EVLOOP_NONBLOCK or not having any active watchers at all will result in not sleeping). - Sleep if the I/O and timer collect interval say so. - Block the process, waiting for any events. - Queue all outstanding I/O (fd) events. - - Update the "event loop time" and do time jump handling. - - Queue all outstanding timers. - - Queue all outstanding periodics. - - If no events are pending now, queue all idle watchers. + - Update the "event loop time" (ev_now ()), and do time jump adjustments. + - Queue all expired timers. + - Queue all expired periodics. + - Unless any events are pending now, queue all idle watchers. - Queue all check watchers. - Call all queued watchers in reverse order (i.e. check watchers first). Signals and child watchers are implemented as I/O watchers, and will @@ -635,7 +680,7 @@ ... queue jobs here, make sure they register event watchers as long ... as they still have work to do (even an idle watcher will do..) ev_loop (my_loop, 0); - ... jobs done. yeah! + ... jobs done or somebody called unloop. yeah! =item ev_unloop (loop, how) @@ -646,18 +691,23 @@ This "unloop state" will be cleared when entering C again. +It is safe to call C from otuside any C calls. + =item ev_ref (loop) =item ev_unref (loop) Ref/unref can be used to add or remove a reference count on the event loop: Every watcher keeps one reference, and as long as the reference -count is nonzero, C will not return on its own. If you have -a watcher you never unregister that should not keep C from -returning, ev_unref() after starting, and ev_ref() before stopping it. For -example, libev itself uses this for its internal signal pipe: It is not -visible to the libev user and should not keep C from exiting if -no event watchers registered by it are active. It is also an excellent +count is nonzero, C will not return on its own. + +If you have a watcher you never unregister that should not keep C +from returning, call ev_unref() after starting, and ev_ref() before +stopping it. + +As an example, libev itself uses this for its internal signal pipe: It is +not visible to the libev user and should not keep C from exiting +if no event watchers registered by it are active. It is also an excellent way to do this for generic recurring timers or from within third-party libraries. Just remember to I and I (but only if the watcher wasn't active before, or was active before, @@ -666,31 +716,33 @@ Example: Create a signal watcher, but keep it from keeping C running when nothing else is active. - struct ev_signal exitsig; - ev_signal_init (&exitsig, sig_cb, SIGINT); - ev_signal_start (loop, &exitsig); - evf_unref (loop); + ev_signal exitsig; + ev_signal_init (&exitsig, sig_cb, SIGINT); + ev_signal_start (loop, &exitsig); + evf_unref (loop); Example: For some weird reason, unregister the above signal handler again. - ev_ref (loop); - ev_signal_stop (loop, &exitsig); + ev_ref (loop); + ev_signal_stop (loop, &exitsig); =item ev_set_io_collect_interval (loop, ev_tstamp interval) =item ev_set_timeout_collect_interval (loop, ev_tstamp interval) These advanced functions influence the time that libev will spend waiting -for events. Both are by default C<0>, meaning that libev will try to -invoke timer/periodic callbacks and I/O callbacks with minimum latency. +for events. Both time intervals are by default C<0>, meaning that libev +will try to invoke timer/periodic callbacks and I/O callbacks with minimum +latency. Setting these to a higher value (the C I be >= C<0>) -allows libev to delay invocation of I/O and timer/periodic callbacks to -increase efficiency of loop iterations. - -The background is that sometimes your program runs just fast enough to -handle one (or very few) event(s) per loop iteration. While this makes -the program responsive, it also wastes a lot of CPU time to poll for new +allows libev to delay invocation of I/O and timer/periodic callbacks +to increase efficiency of loop iterations (or to increase power-saving +opportunities). + +The idea is that sometimes your program runs just fast enough to handle +one (or very few) event(s) per loop iteration. While this makes the +program responsive, it also wastes a lot of CPU time to poll for new events, especially with backends like C function doesn't follow POSIX in that it requires socket I and not socket I (it is also extremely buggy). This makes select very inefficient, and also -requires a mapping from file descriptors to socket handles. See the +requires a mapping from file descriptors to socket handles (the Microsoft +C runtime provides the function C<_open_osfhandle> for this). See the discussion of the C, C and C preprocessor symbols for more info. The configuration for a "naked" win32 using the Microsoft runtime libraries and raw winsocket select is: - #define EV_USE_SELECT 1 - #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */ + #define EV_USE_SELECT 1 + #define EV_SELECT_IS_WINSOCKET 1 /* forces EV_SELECT_USE_FD_SET, too */ Note that winsockets handling of fd sets is O(n), so you can easily get a complexity in the O(n²) range when using win32. @@ -3361,18 +3719,26 @@ =back +=head2 PORTABILITY REQUIREMENTS -=head1 PORTABILITY REQUIREMENTS - -In addition to a working ISO-C implementation, libev relies on a few -additional extensions: +In addition to a working ISO-C implementation and of course the +backend-specific APIs, libev relies on a few additional extensions: =over 4 +=item C must have compatible +calling conventions regardless of C. + +Libev assumes not only that all watcher pointers have the same internal +structure (guaranteed by POSIX but not by ISO C for example), but it also +assumes that the same (machine) code can be used to call any watcher +callback: The watcher callbacks have different type signatures, but libev +calls them using an C internally. + =item C must be thread-atomic as well The type C (or whatever is defined as -C) must be atomic w.r.t. accesses from different +C) must be atomic with respect to accesses from different threads. This is not part of the specification for C, but is believed to be sufficiently portable. @@ -3391,11 +3757,11 @@ =item C must be large enough for common memory allocation sizes -To improve portability and simplify using libev, libev uses C -internally instead of C when allocating its data structures. On -non-POSIX systems (Microsoft...) this might be unexpectedly low, but -is still at least 31 bits everywhere, which is enough for hundreds of -millions of watchers. +To improve portability and simplify its API, libev uses C internally +instead of C when allocating its data structures. On non-POSIX +systems (Microsoft...) this might be unexpectedly low, but is still at +least 31 bits everywhere, which is enough for hundreds of millions of +watchers. =item C must hold a time value in seconds with enough accuracy @@ -3409,56 +3775,75 @@ If you know of other additional requirements drop me a note. -=head1 COMPILER WARNINGS +=head1 ALGORITHMIC COMPLEXITIES -Depending on your compiler and compiler settings, you might get no or a -lot of warnings when compiling libev code. Some people are apparently -scared by this. +In this section the complexities of (many of) the algorithms used inside +libev will be documented. For complexity discussions about backends see +the documentation for C. -However, these are unavoidable for many reasons. For one, each compiler -has different warnings, and each user has different tastes regarding -warning options. "Warn-free" code therefore cannot be a goal except when -targeting a specific compiler and compiler-version. +All of the following are about amortised time: If an array needs to be +extended, libev needs to realloc and move the whole array, but this +happens asymptotically rarer with higher number of elements, so O(1) might +mean that libev does a lengthy realloc operation in rare cases, but on +average it is much faster and asymptotically approaches constant time. -Another reason is that some compiler warnings require elaborate -workarounds, or other changes to the code that make it less clear and less -maintainable. +=over 4 -And of course, some compiler warnings are just plain stupid, or simply -wrong (because they don't actually warn about the condition their message -seems to warn about). +=item Starting and stopping timer/periodic watchers: O(log skipped_other_timers) -While libev is written to generate as few warnings as possible, -"warn-free" code is not a goal, and it is recommended not to build libev -with any compiler warnings enabled unless you are prepared to cope with -them (e.g. by ignoring them). Remember that warnings are just that: -warnings, not errors, or proof of bugs. +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 roughly seven (C) of these watchers. +=item Changing timer/periodic watchers (by autorepeat or calling again): O(log skipped_other_timers) -=head1 VALGRIND +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. -Valgrind has a special section here because it is a popular tool that is -highly useful, but valgrind reports are very hard to interpret. +=item Starting io/check/prepare/idle/signal/child/fork/async watchers: O(1) -If you think you found a bug (memory leak, uninitialised data access etc.) -in libev, then check twice: If valgrind reports something like: +These just add the watcher into an array or at the head of a list. - ==2274== definitely lost: 0 bytes in 0 blocks. - ==2274== possibly lost: 0 bytes in 0 blocks. - ==2274== still reachable: 256 bytes in 1 blocks. +=item Stopping check/prepare/idle/fork/async watchers: O(1) -Then there is no memory leak. Similarly, under some circumstances, -valgrind might report kernel bugs as if it were a bug in libev, or it -might be confused (it is a very good tool, but only a tool). +=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE)) -If you are unsure about something, feel free to contact the mailing list -with the full valgrind report and an explanation on why you think this is -a bug in libev. However, don't be annoyed when you get a brisk "this is -no bug" answer and take the chance of learning how to interpret valgrind -properly. +These watchers are stored in lists, so they 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: one is typical, two +is rare). -If you need, for some reason, empty reports from valgrind for your project -I suggest using suppression lists. +=item Finding the next timer in each loop iteration: O(1) + +By virtue of using a binary or 4-heap, the next timer is always found at a +fixed position in 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 +libev to recalculate its status (and possibly tell the kernel, depending +on backend and whether C was used). + +=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 +linearly search all the priorities, but starting/stopping and activating +watchers becomes O(1) with respect to priority handling. + +=item Sending an ev_async: O(1) + +=item Processing ev_async_send: O(number_of_async_watchers) + +=item Processing signals: O(max_signal_number) + +Sending involves a system call I there were no other C +calls in the current loop iteration. Checking for async and signal events +involves iterating over all running async watchers or all signal numbers. + +=back =head1 AUTHOR