unset cached value - anbody has a better idea to express this?

[software/libev.git] / ev.pod

diff --git a/ev.pod b/ev.pod
index 1b797df5dd8f96b547b1b7c2dc9a90836328ce2e..ed0ac1b9a519e1716e2ceb45874ef263e429dbd3 100644 (file)
--- a/ev.pod
+++ b/ev.pod
@@ -65,12 +65,13 @@ watcher.
 
 =head1 FEATURES
 
 
 =head1 FEATURES
 

-Libev supports C<select>, C<poll>, the linux-specific C<epoll>, the
-bsd-specific C<kqueue> and the solaris-specific event port mechanisms
-for file descriptor events (C<ev_io>), relative timers (C<ev_timer>),
-absolute timers with customised rescheduling (C<ev_periodic>), synchronous
-signals (C<ev_signal>), process status change events (C<ev_child>), and
-event watchers dealing with the event loop mechanism itself (C<ev_idle>,
+Libev supports C<select>, C<poll>, the Linux-specific C<epoll>, the
+BSD-specific C<kqueue> and the Solaris-specific event port mechanisms
+for file descriptor events (C<ev_io>), the Linux C<inotify> interface
+(for C<ev_stat>), relative timers (C<ev_timer>), absolute timers
+with customised rescheduling (C<ev_periodic>), synchronous signals
+(C<ev_signal>), process status change events (C<ev_child>), and event
+watchers dealing with the event loop mechanism itself (C<ev_idle>,

 C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
 file watchers (C<ev_stat>) and even limited support for fork events
 (C<ev_fork>).
 C<ev_embed>, C<ev_prepare> and C<ev_check> watchers) as well as
 file watchers (C<ev_stat>) and even limited support for fork events
 (C<ev_fork>).


@@ -164,13 +165,14 @@ recommended ones.
 
 See the description of C<ev_embed> watchers for more info.
 
 
 See the description of C<ev_embed> watchers for more info.
 

-=item ev_set_allocator (void *(*cb)(void *ptr, size_t size))
+=item ev_set_allocator (void *(*cb)(void *ptr, long size))

 
 

-Sets the allocation function to use (the prototype and semantics are
-identical to the realloc C function). It is used to allocate and free
-memory (no surprises here). If it returns zero when memory needs to be
-allocated, the library might abort or take some potentially destructive
-action. The default is your system realloc function.
+Sets the allocation function to use (the prototype is similar - the
+semantics is identical - to the realloc C function). It is used to
+allocate and free memory (no surprises here). If it returns zero when
+memory needs to be allocated, the library might abort or take some
+potentially destructive action. The default is your system realloc
+function.

 
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,
 
 You could override this function in high-availability programs to, say,
 free some memory if it cannot allocate memory, to use a special allocator,


@@ -266,6 +268,26 @@ override the flags completely if it is found in the environment. This is
 useful to try out specific backends to test their performance, or to work
 around bugs.
 
 useful to try out specific backends to test their performance, or to work
 around bugs.
 

+=item C<EVFLAG_FORKCHECK>
+
+Instead of calling C<ev_default_fork> or C<ev_loop_fork> manually after
+a fork, you can also make libev check for a fork in each iteration by
+enabling this flag.
+
+This works by calling C<getpid ()> on every iteration of the loop,
+and thus this might slow down your event loop if you do a lot of loop
+iterations and little real work, but is usually not noticeable (on my
+Linux system for example, C<getpid> is actually a simple 5-insn sequence
+without a syscall and thus I<very> fast, but my Linux system also has
+C<pthread_atfork> which is even faster).
+
+The big advantage of this flag is that you can forget about fork (and
+forget about forgetting to tell libev about forking) when you use this
+flag.
+
+This flag setting cannot be overriden or specified in the C<LIBEV_FLAGS>
+environment variable.
+

 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 
 This is your standard select(2) backend. Not I<completely> standard, as
 =item C<EVBACKEND_SELECT>  (value 1, portable select backend)
 
 This is your standard select(2) backend. Not I<completely> standard, as


@@ -705,7 +727,7 @@ is pending (but not active) you must not call an init function on it (but
 C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
 libev (e.g. you cnanot C<free ()> it).
 
 C<ev_TYPE_set> is safe) and you must make sure the watcher is available to
 libev (e.g. you cnanot C<free ()> it).
 

-=item callback = ev_cb (ev_TYPE *watcher)
+=item callback ev_cb (ev_TYPE *watcher)

 
 Returns the callback currently set on the watcher.
 
 
 Returns the callback currently set on the watcher.
 


@@ -743,8 +765,37 @@ can cast it back to your own type:
     ...
   }
 
     ...
   }
 

-More interesting and less C-conformant ways of catsing your callback type
-have been omitted....
+More interesting and less C-conformant ways of casting your callback type
+instead have been omitted.
+
+Another common scenario is having some data structure with multiple
+watchers:
+
+  struct my_biggy
+  {
+    int some_data;
+    ev_timer t1;
+    ev_timer t2;
+  }
+
+In this case getting the pointer to C<my_biggy> is a bit more complicated,
+you need to use C<offsetof>:
+
+  #include <stddef.h>
+
+  static void
+  t1_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    struct my_biggy big = (struct my_biggy *
+      (((char *)w) - offsetof (struct my_biggy, t1));
+  }
+
+  static void
+  t2_cb (EV_P_ struct ev_timer *w, int revents)
+  {
+    struct my_biggy big = (struct my_biggy *
+      (((char *)w) - offsetof (struct my_biggy, t2));
+  }

 
 
 =head1 WATCHER TYPES
 
 
 =head1 WATCHER TYPES


@@ -887,23 +938,25 @@ timer will not fire more than once per event loop iteration.
 This will act as if the timer timed out and restart it again if it is
 repeating. The exact semantics are:
 
 This will act as if the timer timed out and restart it again if it is
 repeating. The exact semantics are:
 

-If the timer is started but nonrepeating, stop it.
+If the timer is pending, its pending status is cleared.
+
+If the timer is started but nonrepeating, stop it (as if it timed out).

 
 

-If the timer is repeating, either start it if necessary (with the repeat
-value), or reset the running timer to the repeat value.
+If the timer is repeating, either start it if necessary (with the
+C<repeat> value), or reset the running timer to the C<repeat> value.

 
 This sounds a bit complicated, but here is a useful and typical
 
 This sounds a bit complicated, but here is a useful and typical

-example: Imagine you have a tcp connection and you want a so-called
-idle timeout, that is, you want to be called when there have been,
-say, 60 seconds of inactivity on the socket. The easiest way to do
-this is to configure an C<ev_timer> with C<after>=C<repeat>=C<60> and calling
+example: Imagine you have a tcp connection and you want a so-called idle
+timeout, that is, you want to be called when there have been, say, 60
+seconds of inactivity on the socket. The easiest way to do this is to
+configure an C<ev_timer> with a C<repeat> value of C<60> and then call

 C<ev_timer_again> each time you successfully read or write some data. If
 you go into an idle state where you do not expect data to travel on the
 C<ev_timer_again> each time you successfully read or write some data. If
 you go into an idle state where you do not expect data to travel on the

-socket, you can stop the timer, and again will automatically restart it if
-need be.
+socket, you can C<ev_timer_stop> the timer, and C<ev_timer_again> will
+automatically restart it if need be.

 
 

-You can also ignore the C<after> value and C<ev_timer_start> altogether
-and only ever use the C<repeat> value:
+That means you can ignore the C<after> value and C<ev_timer_start>
+altogether and only ever use the C<repeat> value and C<ev_timer_again>:

 
    ev_timer_init (timer, callback, 0., 5.);
    ev_timer_again (loop, timer);
 
    ev_timer_init (timer, callback, 0., 5.);
    ev_timer_again (loop, timer);


@@ -914,8 +967,8 @@ and only ever use the C<repeat> value:
    timer->again = 10.;
    ev_timer_again (loop, timer);
 
    timer->again = 10.;
    ev_timer_again (loop, timer);
 

-This is more efficient then stopping/starting the timer eahc time you want
-to modify its timeout value.
+This is more slightly efficient then stopping/starting the timer each time
+you want to modify its timeout value.

 
 =item ev_tstamp repeat [read-write]
 
 
 =item ev_tstamp repeat [read-write]
 


@@ -1194,8 +1247,11 @@ not exist" is signified by the C<st_nlink> field being zero (which is
 otherwise always forced to be at least one) and all the other fields of
 the stat buffer having unspecified contents.
 
 otherwise always forced to be at least one) and all the other fields of
 the stat buffer having unspecified contents.
 

+The path I<should> be absolute and I<must not> end in a slash. If it is
+relative and your working directory changes, the behaviour is undefined.
+

 Since there is no standard to do this, the portable implementation simply
 Since there is no standard to do this, the portable implementation simply

-calls C<stat (2)> regulalry on the path to see if it changed somehow. You
+calls C<stat (2)> regularly on the path to see if it changed somehow. You

 can specify a recommended polling interval for this case. If you specify
 a polling interval of C<0> (highly recommended!) then a I<suitable,
 unspecified default> value will be used (which you can expect to be around
 can specify a recommended polling interval for this case. If you specify
 a polling interval of C<0> (highly recommended!) then a I<suitable,
 unspecified default> value will be used (which you can expect to be around


@@ -1207,8 +1263,13 @@ This watcher type is not meant for massive numbers of stat watchers,
 as even with OS-supported change notifications, this can be
 resource-intensive.
 
 as even with OS-supported change notifications, this can be
 resource-intensive.
 

-At the time of this writing, no specific OS backends are implemented, but
-if demand increases, at least a kqueue and inotify backend will be added.
+At the time of this writing, only the Linux inotify interface is
+implemented (implementing kqueue support is left as an exercise for the
+reader). Inotify will be used to give hints only and should not change the
+semantics of C<ev_stat> watchers, which means that libev sometimes needs
+to fall back to regular polling again even with inotify, but changes are
+usually detected immediately, and if the file exists there will be no
+polling.

 
 =over 4
 
 
 =over 4
 


@@ -1398,7 +1459,8 @@ pseudo-code only of course:
   static void
   adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
   {
   static void
   adns_prepare_cb (ev_loop *loop, ev_prepare *w, int revents)
   {

-    int timeout = 3600000;truct pollfd fds [nfd];
+    int timeout = 3600000;
+    struct pollfd fds [nfd];

     // actual code will need to loop here and realloc etc.
     adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
 
     // actual code will need to loop here and realloc etc.
     adns_beforepoll (ads, fds, &nfd, &timeout, timeval_from (ev_time ()));
 


@@ -1789,8 +1851,9 @@ loop, if multiple loops are supported ("ev loop default").
 
 =back
 
 
 =back
 

-Example: Declare and initialise a check watcher, working regardless of
-wether multiple loops are supported or not.
+Example: Declare and initialise a check watcher, utilising the above
+macros so it will work regardless of wether multiple loops are supported
+or not.

 
   static void
   check_cb (EV_P_ ev_timer *w, int revents)
 
   static void
   check_cb (EV_P_ ev_timer *w, int revents)


@@ -1803,7 +1866,6 @@ wether multiple loops are supported or not.
   ev_check_start (EV_DEFAULT_ &check);
   ev_loop (EV_DEFAULT_ 0);
 
   ev_check_start (EV_DEFAULT_ &check);
   ev_loop (EV_DEFAULT_ 0);
 

-

 =head1 EMBEDDING
 
 Libev can (and often is) directly embedded into host
 =head1 EMBEDDING
 
 Libev can (and often is) directly embedded into host


@@ -1852,7 +1914,7 @@ in your include path (e.g. in libev/ when using -Ilibev):
 
   ev_win32.c      required on win32 platforms only
 
 
   ev_win32.c      required on win32 platforms only
 

-  ev_select.c     only when select backend is enabled (which is by default)
+  ev_select.c     only when select backend is enabled (which is enabled by default)

   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)
   ev_poll.c       only when poll backend is enabled (disabled by default)
   ev_epoll.c      only when the epoll backend is enabled (disabled by default)
   ev_kqueue.c     only when the kqueue backend is enabled (disabled by default)


@@ -1987,6 +2049,12 @@ backend for Solaris 10 systems.
 
 reserved for future expansion, works like the USE symbols above.
 
 
 reserved for future expansion, works like the USE symbols above.
 

+=item EV_USE_INOTIFY
+
+If defined to be C<1>, libev will compile in support for the Linux inotify
+interface to speed up C<ev_stat> watchers. Its actual availability will
+be detected at runtime.
+

 =item EV_H
 
 The name of the F<ev.h> header file used to include it. The default if
 =item EV_H
 
 The name of the F<ev.h> header file used to include it. The default if


@@ -2051,7 +2119,15 @@ some inlining decisions, saves roughly 30% codesize of amd64.
 C<ev_child> watchers use a small hash table to distribute workload by
 pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
 than enough. If you need to manage thousands of children you might want to
 C<ev_child> watchers use a small hash table to distribute workload by
 pid. The default size is C<16> (or C<1> with C<EV_MINIMAL>), usually more
 than enough. If you need to manage thousands of children you might want to

-increase this value.
+increase this value (I<must> be a power of two).
+
+=item EV_INOTIFY_HASHSIZE
+
+C<ev_staz> 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
+two).

 
 =item EV_COMMON
 
 
 =item EV_COMMON
 


@@ -2090,12 +2166,17 @@ will be compiled. It is pretty complex because it provides its own header
 file.
 
 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file
 file.
 
 The usage in rxvt-unicode is simpler. It has a F<ev_cpp.h> header file

-that everybody includes and which overrides some autoconf choices:
+that everybody includes and which overrides some configure choices:

 
 

+  #define EV_MINIMAL 1

   #define EV_USE_POLL 0
   #define EV_MULTIPLICITY 0
   #define EV_USE_POLL 0
   #define EV_MULTIPLICITY 0

-  #define EV_PERIODICS 0
+  #define EV_PERIODIC_ENABLE 0
+  #define EV_STAT_ENABLE 0
+  #define EV_FORK_ENABLE 0

   #define EV_CONFIG_H <config.h>
   #define EV_CONFIG_H <config.h>

+  #define EV_MINPRI 0
+  #define EV_MAXPRI 0

 
   #include "ev++.h"
 
 
   #include "ev++.h"
 


@@ -2121,7 +2202,7 @@ documentation for C<ev_default_init>.
 
 =item Stopping check/prepare/idle watchers: O(1)
 
 
 =item Stopping check/prepare/idle watchers: O(1)
 

-=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % 16))
+=item Stopping an io/signal/child watcher: O(number_of_watchers_for_this_(fd/signal/pid % EV_PID_HASHSIZE))

 
 =item Finding the next timer per loop iteration: O(1)
 
 
 =item Finding the next timer per loop iteration: O(1)