… | |
… | |
1538 | |
1538 | |
1539 | So when you encounter spurious, unexplained daemon exits, make sure you |
1539 | So when you encounter spurious, unexplained daemon exits, make sure you |
1540 | ignore SIGPIPE (and maybe make sure you log the exit status of your daemon |
1540 | ignore SIGPIPE (and maybe make sure you log the exit status of your daemon |
1541 | somewhere, as that would have given you a big clue). |
1541 | somewhere, as that would have given you a big clue). |
1542 | |
1542 | |
|
|
1543 | =head3 The special problem of accept()ing when you can't |
|
|
1544 | |
|
|
1545 | Many implementations of the POSIX C<accept> function (for example, |
|
|
1546 | found in port-2004 Linux) have the peculiar behaviour of not removing a |
|
|
1547 | connection from the pending queue in all error cases. |
|
|
1548 | |
|
|
1549 | For example, larger servers often run out of file descriptors (because |
|
|
1550 | of resource limits), causing C<accept> to fail with C<ENFILE> but not |
|
|
1551 | rejecting the connection, leading to libev signalling readiness on |
|
|
1552 | the next iteration again (the connection still exists after all), and |
|
|
1553 | typically causing the program to loop at 100% CPU usage. |
|
|
1554 | |
|
|
1555 | Unfortunately, the set of errors that cause this issue differs between |
|
|
1556 | operating systems, there is usually little the app can do to remedy the |
|
|
1557 | situation, and no known thread-safe method of removing the connection to |
|
|
1558 | cope with overload is known (to me). |
|
|
1559 | |
|
|
1560 | One of the easiest ways to handle this situation is to just ignore it |
|
|
1561 | - when the program encounters an overload, it will just loop until the |
|
|
1562 | situation is over. While this is a form of busy waiting, no OS offers an |
|
|
1563 | event-based way to handle this situation, so it's the best one can do. |
|
|
1564 | |
|
|
1565 | A better way to handle the situation is to log any errors other than |
|
|
1566 | C<EAGAIN> and C<EWOULDBLOCK>, making sure not to flood the log with such |
|
|
1567 | messages, and continue as usual, which at least gives the user an idea of |
|
|
1568 | what could be wrong ("raise the ulimit!"). For extra points one could stop |
|
|
1569 | the C<ev_io> watcher on the listening fd "for a while", which reduces CPU |
|
|
1570 | usage. |
|
|
1571 | |
|
|
1572 | If your program is single-threaded, then you could also keep a dummy file |
|
|
1573 | descriptor for overload situations (e.g. by opening F</dev/null>), and |
|
|
1574 | when you run into C<ENFILE> or C<EMFILE>, close it, run C<accept>, |
|
|
1575 | close that fd, and create a new dummy fd. This will gracefully refuse |
|
|
1576 | clients under typical overload conditions. |
|
|
1577 | |
|
|
1578 | The last way to handle it is to simply log the error and C<exit>, as |
|
|
1579 | is often done with C<malloc> failures, but this results in an easy |
|
|
1580 | opportunity for a DoS attack. |
1543 | |
1581 | |
1544 | =head3 Watcher-Specific Functions |
1582 | =head3 Watcher-Specific Functions |
1545 | |
1583 | |
1546 | =over 4 |
1584 | =over 4 |
1547 | |
1585 | |
… | |
… | |
3838 | fine. |
3876 | fine. |
3839 | |
3877 | |
3840 | If your embedding application does not need any priorities, defining these |
3878 | If your embedding application does not need any priorities, defining these |
3841 | both to C<0> will save some memory and CPU. |
3879 | both to C<0> will save some memory and CPU. |
3842 | |
3880 | |
3843 | =item EV_PERIODIC_ENABLE |
3881 | =item EV_PERIODIC_ENABLE, EV_IDLE_ENABLE, EV_EMBED_ENABLE, EV_STAT_ENABLE, |
|
|
3882 | EV_PREPARE_ENABLE, EV_CHECK_ENABLE, EV_FORK_ENABLE, EV_SIGNAL_ENABLE, |
|
|
3883 | EV_ASYNC_ENABLE, EV_CHILD_ENABLE. |
3844 | |
3884 | |
3845 | If undefined or defined to be C<1>, then periodic timers are supported. If |
3885 | If undefined or defined to be C<1> (and the platform supports it), then |
3846 | defined to be C<0>, then they are not. Disabling them saves a few kB of |
3886 | the respective watcher type is supported. If defined to be C<0>, then it |
3847 | code. |
3887 | is not. Disabling watcher types mainly saves codesize. |
3848 | |
3888 | |
3849 | =item EV_IDLE_ENABLE |
3889 | =item EV_FEATURES |
3850 | |
|
|
3851 | If undefined or defined to be C<1>, then idle watchers are supported. If |
|
|
3852 | defined to be C<0>, then they are not. Disabling them saves a few kB of |
|
|
3853 | code. |
|
|
3854 | |
|
|
3855 | =item EV_EMBED_ENABLE |
|
|
3856 | |
|
|
3857 | If undefined or defined to be C<1>, then embed watchers are supported. If |
|
|
3858 | defined to be C<0>, then they are not. Embed watchers rely on most other |
|
|
3859 | watcher types, which therefore must not be disabled. |
|
|
3860 | |
|
|
3861 | =item EV_STAT_ENABLE |
|
|
3862 | |
|
|
3863 | If undefined or defined to be C<1>, then stat watchers are supported. If |
|
|
3864 | defined to be C<0>, then they are not. |
|
|
3865 | |
|
|
3866 | =item EV_FORK_ENABLE |
|
|
3867 | |
|
|
3868 | If undefined or defined to be C<1>, then fork watchers are supported. If |
|
|
3869 | defined to be C<0>, then they are not. |
|
|
3870 | |
|
|
3871 | =item EV_ASYNC_ENABLE |
|
|
3872 | |
|
|
3873 | If undefined or defined to be C<1>, then async watchers are supported. If |
|
|
3874 | defined to be C<0>, then they are not. |
|
|
3875 | |
|
|
3876 | =item EV_MINIMAL |
|
|
3877 | |
3890 | |
3878 | If you need to shave off some kilobytes of code at the expense of some |
3891 | If you need to shave off some kilobytes of code at the expense of some |
3879 | speed (but with the full API), define this symbol to C<1>. Currently this |
3892 | speed (but with the full API), you can define this symbol to request |
3880 | is used to override some inlining decisions, saves roughly 30% code size |
3893 | certain subsets of functionality. The default is to enable all features |
3881 | on amd64. It also selects a much smaller 2-heap for timer management over |
3894 | that can be enabled on the platform. |
3882 | the default 4-heap. |
|
|
3883 | |
3895 | |
3884 | You can save even more by disabling watcher types you do not need |
3896 | A typical way to use this symbol is to define it to C<0> (or to a bitset |
3885 | and setting C<EV_MAXPRI> == C<EV_MINPRI>. Also, disabling C<assert> |
3897 | with some broad features you want) and then selectively re-enable |
3886 | (C<-DNDEBUG>) will usually reduce code size a lot. |
3898 | additional parts you want, for example if you want everything minimal, |
|
|
3899 | but multiple event loop support, async and child watchers and the poll |
|
|
3900 | backend, use this: |
3887 | |
3901 | |
3888 | Defining C<EV_MINIMAL> to C<2> will additionally reduce the core API to |
3902 | #define EV_FEATURES 0 |
3889 | provide a bare-bones event library. See C<ev.h> for details on what parts |
3903 | #define EV_MULTIPLICITY 1 |
3890 | of the API are still available, and do not complain if this subset changes |
3904 | #define EV_USE_POLL 1 |
3891 | over time. |
3905 | #define EV_CHILD_ENABLE 1 |
|
|
3906 | #define EV_ASYNC_ENABLE 1 |
|
|
3907 | |
|
|
3908 | The actual value is a bitset, it can be a combination of the following |
|
|
3909 | values: |
|
|
3910 | |
|
|
3911 | =over 4 |
|
|
3912 | |
|
|
3913 | =item C<1> - faster/larger code |
|
|
3914 | |
|
|
3915 | Use larger code to speed up some operations. |
|
|
3916 | |
|
|
3917 | Currently this is used to override some inlining decisions (enlarging the roughly |
|
|
3918 | 30% code size on amd64. |
|
|
3919 | |
|
|
3920 | When optimising for size, use of compiler flags such as C<-Os> with |
|
|
3921 | gcc recommended, as well as C<-DNDEBUG>, as libev contains a number of |
|
|
3922 | assertions. |
|
|
3923 | |
|
|
3924 | =item C<2> - faster/larger data structures |
|
|
3925 | |
|
|
3926 | Replaces the small 2-heap for timer management by a faster 4-heap, larger |
|
|
3927 | hash table sizes and so on. This will usually further increase codesize |
|
|
3928 | and can additionally have an effect on the size of data structures at |
|
|
3929 | runtime. |
|
|
3930 | |
|
|
3931 | =item C<4> - full API configuration |
|
|
3932 | |
|
|
3933 | This enables priorities (sets C<EV_MAXPRI>=2 and C<EV_MINPRI>=-2), and |
|
|
3934 | enables multiplicity (C<EV_MULTIPLICITY>=1). |
|
|
3935 | |
|
|
3936 | =item C<8> - full API |
|
|
3937 | |
|
|
3938 | This enables a lot of the "lesser used" API functions. See C<ev.h> for |
|
|
3939 | details on which parts of the API are still available without this |
|
|
3940 | feature, and do not complain if this subset changes over time. |
|
|
3941 | |
|
|
3942 | =item C<16> - enable all optional watcher types |
|
|
3943 | |
|
|
3944 | Enables all optional watcher types. If you want to selectively enable |
|
|
3945 | only some watcher types other than I/O and timers (e.g. prepare, |
|
|
3946 | embed, async, child...) you can enable them manually by defining |
|
|
3947 | C<EV_watchertype_ENABLE> to C<1> instead. |
|
|
3948 | |
|
|
3949 | =item C<32> - enable all backends |
|
|
3950 | |
|
|
3951 | This enables all backends - without this feature, you need to enable at |
|
|
3952 | least one backend manually (C<EV_USE_SELECT> is a good choice). |
|
|
3953 | |
|
|
3954 | =item C<64> - enable OS-specific "helper" APIs |
|
|
3955 | |
|
|
3956 | Enable inotify, eventfd, signalfd and similar OS-specific helper APIs by |
|
|
3957 | default. |
|
|
3958 | |
|
|
3959 | =back |
|
|
3960 | |
|
|
3961 | Compiling with C<gcc -Os -DEV_STANDALONE -DEV_USE_EPOLL=1 -DEV_FEATURES=0> |
|
|
3962 | reduces the compiled size of libev from 24.7Kb to 6.5Kb on my GNU/Linux |
|
|
3963 | amd64 system, while still giving you I/O watchers, timers and monotonic |
|
|
3964 | clock support. |
|
|
3965 | |
|
|
3966 | With an intelligent-enough linker (gcc+binutils are intelligent enough |
|
|
3967 | when you use C<-Wl,--gc-sections -ffunction-sections>) functions unused by |
|
|
3968 | your program might be left out as well - a binary starting a timer and an |
|
|
3969 | I/O watcher then might come out at only 5Kb. |
3892 | |
3970 | |
3893 | =item EV_AVOID_STDIO |
3971 | =item EV_AVOID_STDIO |
3894 | |
3972 | |
3895 | If this is set to C<1> at compiletime, then libev will avoid using stdio |
3973 | If this is set to C<1> at compiletime, then libev will avoid using stdio |
3896 | functions (printf, scanf, perror etc.). This will increase the codesize |
3974 | functions (printf, scanf, perror etc.). This will increase the codesize |
… | |
… | |
3911 | statically allocates some 12-24 bytes per signal number. |
3989 | statically allocates some 12-24 bytes per signal number. |
3912 | |
3990 | |
3913 | =item EV_PID_HASHSIZE |
3991 | =item EV_PID_HASHSIZE |
3914 | |
3992 | |
3915 | C<ev_child> watchers use a small hash table to distribute workload by |
3993 | C<ev_child> watchers use a small hash table to distribute workload by |
3916 | pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more |
3994 | pid. The default size is C<16> (or C<1> with C<EV_FEATURES> disabled), |
3917 | than enough. If you need to manage thousands of children you might want to |
3995 | usually more than enough. If you need to manage thousands of children you |
3918 | increase this value (I<must> be a power of two). |
3996 | might want to increase this value (I<must> be a power of two). |
3919 | |
3997 | |
3920 | =item EV_INOTIFY_HASHSIZE |
3998 | =item EV_INOTIFY_HASHSIZE |
3921 | |
3999 | |
3922 | C<ev_stat> watchers use a small hash table to distribute workload by |
4000 | C<ev_stat> watchers use a small hash table to distribute workload by |
3923 | inotify watch id. The default size is C<16> (or C<1> with C<EV_MINIMAL>), |
4001 | inotify watch id. The default size is C<16> (or C<1> with C<EV_FEATURES> |
3924 | usually more than enough. If you need to manage thousands of C<ev_stat> |
4002 | disabled), usually more than enough. If you need to manage thousands of |
3925 | watchers you might want to increase this value (I<must> be a power of |
4003 | C<ev_stat> watchers you might want to increase this value (I<must> be a |
3926 | two). |
4004 | power of two). |
3927 | |
4005 | |
3928 | =item EV_USE_4HEAP |
4006 | =item EV_USE_4HEAP |
3929 | |
4007 | |
3930 | Heaps are not very cache-efficient. To improve the cache-efficiency of the |
4008 | Heaps are not very cache-efficient. To improve the cache-efficiency of the |
3931 | timer and periodics heaps, libev uses a 4-heap when this symbol is defined |
4009 | timer and periodics heaps, libev uses a 4-heap when this symbol is defined |
3932 | to C<1>. The 4-heap uses more complicated (longer) code but has noticeably |
4010 | to C<1>. The 4-heap uses more complicated (longer) code but has noticeably |
3933 | faster performance with many (thousands) of watchers. |
4011 | faster performance with many (thousands) of watchers. |
3934 | |
4012 | |
3935 | The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0> |
4013 | The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it |
3936 | (disabled). |
4014 | will be C<0>. |
3937 | |
4015 | |
3938 | =item EV_HEAP_CACHE_AT |
4016 | =item EV_HEAP_CACHE_AT |
3939 | |
4017 | |
3940 | Heaps are not very cache-efficient. To improve the cache-efficiency of the |
4018 | Heaps are not very cache-efficient. To improve the cache-efficiency of the |
3941 | timer and periodics heaps, libev can cache the timestamp (I<at>) within |
4019 | timer and periodics heaps, libev can cache the timestamp (I<at>) within |
3942 | the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>), |
4020 | the heap structure (selected by defining C<EV_HEAP_CACHE_AT> to C<1>), |
3943 | which uses 8-12 bytes more per watcher and a few hundred bytes more code, |
4021 | which uses 8-12 bytes more per watcher and a few hundred bytes more code, |
3944 | but avoids random read accesses on heap changes. This improves performance |
4022 | but avoids random read accesses on heap changes. This improves performance |
3945 | noticeably with many (hundreds) of watchers. |
4023 | noticeably with many (hundreds) of watchers. |
3946 | |
4024 | |
3947 | The default is C<1> unless C<EV_MINIMAL> is set in which case it is C<0> |
4025 | The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it |
3948 | (disabled). |
4026 | will be C<0>. |
3949 | |
4027 | |
3950 | =item EV_VERIFY |
4028 | =item EV_VERIFY |
3951 | |
4029 | |
3952 | Controls how much internal verification (see C<ev_loop_verify ()>) will |
4030 | Controls how much internal verification (see C<ev_loop_verify ()>) will |
3953 | be done: If set to C<0>, no internal verification code will be compiled |
4031 | be done: If set to C<0>, no internal verification code will be compiled |
… | |
… | |
3955 | called. If set to C<2>, then the internal verification code will be |
4033 | called. If set to C<2>, then the internal verification code will be |
3956 | called once per loop, which can slow down libev. If set to C<3>, then the |
4034 | called once per loop, which can slow down libev. If set to C<3>, then the |
3957 | verification code will be called very frequently, which will slow down |
4035 | verification code will be called very frequently, which will slow down |
3958 | libev considerably. |
4036 | libev considerably. |
3959 | |
4037 | |
3960 | The default is C<1>, unless C<EV_MINIMAL> is set, in which case it will be |
4038 | The default is C<1>, unless C<EV_FEATURES> overrides it, in which case it |
3961 | C<0>. |
4039 | will be C<0>. |
3962 | |
4040 | |
3963 | =item EV_COMMON |
4041 | =item EV_COMMON |
3964 | |
4042 | |
3965 | By default, all watchers have a C<void *data> member. By redefining |
4043 | By default, all watchers have a C<void *data> member. By redefining |
3966 | this macro to a something else you can include more and other types of |
4044 | this macro to a something else you can include more and other types of |
… | |
… | |
4024 | file. |
4102 | file. |
4025 | |
4103 | |
4026 | The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file |
4104 | The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file |
4027 | that everybody includes and which overrides some configure choices: |
4105 | that everybody includes and which overrides some configure choices: |
4028 | |
4106 | |
4029 | #define EV_MINIMAL 1 |
4107 | #define EV_FEATURES 8 |
4030 | #define EV_USE_POLL 0 |
4108 | #define EV_USE_SELECT 1 |
4031 | #define EV_MULTIPLICITY 0 |
|
|
4032 | #define EV_PERIODIC_ENABLE 0 |
4109 | #define EV_PREPARE_ENABLE 1 |
|
|
4110 | #define EV_IDLE_ENABLE 1 |
4033 | #define EV_STAT_ENABLE 0 |
4111 | #define EV_SIGNAL_ENABLE 1 |
4034 | #define EV_FORK_ENABLE 0 |
4112 | #define EV_CHILD_ENABLE 1 |
|
|
4113 | #define EV_USE_STDEXCEPT 0 |
4035 | #define EV_CONFIG_H <config.h> |
4114 | #define EV_CONFIG_H <config.h> |
4036 | #define EV_MINPRI 0 |
|
|
4037 | #define EV_MAXPRI 0 |
|
|
4038 | |
4115 | |
4039 | #include "ev++.h" |
4116 | #include "ev++.h" |
4040 | |
4117 | |
4041 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4118 | And a F<ev_cpp.C> implementation file that contains libev proper and is compiled: |
4042 | |
4119 | |