[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC vs.
Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC

-=> NAME
+NAME
     AnyEvent - provide framework for multiple event loops
     EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
     loops
        my $w = AnyEvent->condvar; # stores whether a condition was flagged
        $w->send; # wake up current and all future recv's
        $w->recv; # enters "main loop" till $condvar gets ->send
+INTRODUCTION/TUTORIAL
+    This manpage is mainly a reference manual. If you are interested in a
+    tutorial or some gentle introduction, have a look at the AnyEvent::Intro
+    manpage.
 WHY YOU SHOULD USE THIS MODULE (OR NOT)
     Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
     nowadays. So what is different about AnyEvent?
     Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
     policy* and AnyEvent is *small and efficient*.
     First and foremost, *AnyEvent is not an event model* itself, it only
-    interfaces to whatever event model the main program happens to use in a
+    interfaces to whatever event model the main program happens to use, in a
     pragmatic way. For event models and certain classes of immortals alike,
     the statement "there can only be one" is a bitter reality: In general,
     only one event loop can be active at the same time in a process.
-    AnyEvent helps hiding the differences between those event loops.
+    AnyEvent cannot change this, but it can hide the differences between
+    those event loops.
     The goal of AnyEvent is to offer module authors the ability to do event
     programming (waiting for I/O or timer events) without subscribing to a
     religion, a way of living, and most importantly: without forcing your
     module users into the same thing by forcing them to use the same event
     model you use.
     For modules like POE or IO::Async (which is a total misnomer as it is
     actually doing all I/O *synchronously*...), using them in your module is
     like joining a cult: After you joined, you are dependent on them and you
-    cannot use anything else, as it is simply incompatible to everything
+    cannot use anything else, as they are simply incompatible to everything
-    that isn't itself. What's worse, all the potential users of your module
+    that isn't them. What's worse, all the potential users of your module
     are *also* forced to use the same event loop you use.
     AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
     fine. AnyEvent + Tk works fine etc. etc. but none of these work together
-    with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if your
+    with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your
     module uses one of those, every user of your module has to use it, too.
     But if your module uses AnyEvent, it works transparently with all event
-    models it supports (including stuff like POE and IO::Async, as long as
+    models it supports (including stuff like IO::Async, as long as those use
-    those use one of the supported event loops. It is trivial to add new
+    one of the supported event loops. It is trivial to add new event loops
-    event loops to AnyEvent, too, so it is future-proof).
+    to AnyEvent, too, so it is future-proof).
     In addition to being free of having to use *the one and only true event
     model*, AnyEvent also is free of bloat and policy: with POE or similar
     modules, you get an enormous amount of code and strict rules you have to
     follow. AnyEvent, on the other hand, is lean and up to the point, by
     only offering the functionality that is necessary, in as thin as a
     wrapper as technically possible.
+    Of course, AnyEvent comes with a big (and fully optional!) toolbox of
+    useful functionality, such as an asynchronous DNS resolver, 100%
+    non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
+    such as Windows) and lots of real-world knowledge and workarounds for
+    platform bugs and differences.
-    Of course, if you want lots of policy (this can arguably be somewhat
+    Now, if you *do want* lots of policy (this can arguably be somewhat
     useful) and you want to force your users to use the one and only event
     model, you should *not* use this module.
 DESCRIPTION
     AnyEvent provides an identical interface to multiple event loops. This
     starts using it, all bets are off. Maybe you should tell their authors
     to use AnyEvent so their modules work together with others seamlessly...
     The pure-perl implementation of AnyEvent is called
     "AnyEvent::Impl::Perl". Like other event modules you can load it
-    explicitly.
+    explicitly and enjoy the high availability of that event loop :)
 WATCHERS
     AnyEvent has the central concept of a *watcher*, which is an object that
     stores relevant data for each kind of event you are waiting for, such as
     the callback to call, the file handle to watch, etc.
     Many watchers either are used with "recursion" (repeating timers for
     example), or need to refer to their watcher object in other ways.
     An any way to achieve that is this pattern:
-      my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
+       my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
-         # you can use $w here, for example to undef it
+          # you can use $w here, for example to undef it
-         undef $w;
+          undef $w;
-      });
+       });
     Note that "my $w; $w =" combination. This is necessary because in Perl,
     my variables are only visible after the statement in which they are
     declared.
   I/O WATCHERS
     You can create an I/O watcher by calling the "AnyEvent->io" method with
     the following mandatory key-value pairs as arguments:
-    "fh" the Perl *file handle* (*not* file descriptor) to watch for events.
+    "fh" the Perl *file handle* (*not* file descriptor) to watch for events
+    (AnyEvent might or might not keep a reference to this file handle).
     "poll" must be a string that is either "r" or "w", which creates a
     watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
     is the callback to invoke each time the file handle becomes ready.
     Although the callback might get passed parameters, their value and
     Some event loops issue spurious readyness notifications, so you should
     always use non-blocking calls when reading/writing from/to your file
     handles.
-    Example:
-       # wait for readability of STDIN, then read a line and disable the watcher
+    Example: wait for readability of STDIN, then read a line and disable the
+    watcher.
        my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
           chomp (my $input = <STDIN>);
           warn "read: $input\n";
           undef $w;
        });
     Although the callback might get passed parameters, their value and
     presence is undefined and you cannot rely on them. Portable AnyEvent
     callbacks cannot use arguments passed to time watcher callbacks.
-    The timer callback will be invoked at most once: if you want a repeating
+    The callback will normally be invoked once only. If you specify another
-    timer you have to create a new watcher (this is a limitation by both Tk
+    parameter, "interval", as a strictly positive number (> 0), then the
-    and Glib).
+    callback will be invoked regularly at that interval (in fractional
+    seconds) after the first invocation. If "interval" is specified with a
+    false value, then it is treated as if it were missing.
-    Example:
+    The callback will be rescheduled before invoking the callback, but no
+    attempt is done to avoid timer drift in most backends, so the interval
+    is only approximate.
-       # fire an event after 7.7 seconds
+    Example: fire an event after 7.7 seconds.
        my $w = AnyEvent->timer (after => 7.7, cb => sub {
           warn "timeout\n";
        });
        # to cancel the timer:
        undef $w;
-    Example 2:
-       # fire an event after 0.5 seconds, then roughly every second
+    Example 2: fire an event after 0.5 seconds, then roughly every second.
-       my $w;
-       my $cb = sub {
-          # cancel the old timer while creating a new one
-          $w = AnyEvent->timer (after => 1, cb => $cb);
+       my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
+          warn "timeout\n";
        };
-       # start the "loop" by creating the first watcher
-       $w = AnyEvent->timer (after => 0.5, cb => $cb);
    TIMING ISSUES
     There are two ways to handle timers: based on real time (relative, "fire
     in 10 seconds") and based on wallclock time (absolute, "fire at 12
     o'clock").
     on wallclock time) timers.
     AnyEvent always prefers relative timers, if available, matching the
     AnyEvent API.
+    AnyEvent has two additional methods that return the "current time":
+    AnyEvent->time
+        This returns the "current wallclock time" as a fractional number of
+        seconds since the Epoch (the same thing as "time" or
+        "Time::HiRes::time" return, and the result is guaranteed to be
+        compatible with those).
+        It progresses independently of any event loop processing, i.e. each
+        call will check the system clock, which usually gets updated
+        frequently.
+    AnyEvent->now
+        This also returns the "current wallclock time", but unlike "time",
+        above, this value might change only once per event loop iteration,
+        depending on the event loop (most return the same time as "time",
+        above). This is the time that AnyEvent's timers get scheduled
+        against.
+        *In almost all cases (in all cases if you don't care), this is the
+        function to call when you want to know the current time.*
+        This function is also often faster then "AnyEvent->time", and thus
+        the preferred method if you want some timestamp (for example,
+        AnyEvent::Handle uses this to update it's activity timeouts).
+        The rest of this section is only of relevance if you try to be very
+        exact with your timing, you can skip it without bad conscience.
+        For a practical example of when these times differ, consider
+        Event::Lib and EV and the following set-up:
+        The event loop is running and has just invoked one of your callback
+        at time=500 (assume no other callbacks delay processing). In your
+        callback, you wait a second by executing "sleep 1" (blocking the
+        process for a second) and then (at time=501) you create a relative
+        timer that fires after three seconds.
+        With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both
+        return 501, because that is the current time, and the timer will be
+        scheduled to fire at time=504 (501 + 3).
+        With EV, "AnyEvent->time" returns 501 (as that is the current time),
+        but "AnyEvent->now" returns 500, as that is the time the last event
+        processing phase started. With EV, your timer gets scheduled to run
+        at time=503 (500 + 3).
+        In one sense, Event::Lib is more exact, as it uses the current time
+        regardless of any delays introduced by event processing. However,
+        most callbacks do not expect large delays in processing, so this
+        causes a higher drift (and a lot more system calls to get the
+        current time).
+        In another sense, EV is more exact, as your timer will be scheduled
+        at the same time, regardless of how long event processing actually
+        took.
+        In either case, if you care (and in most cases, you don't), then you
+        can get whatever behaviour you want with any event loop, by taking
+        the difference between "AnyEvent->time" and "AnyEvent->now" into
+        account.
   SIGNAL WATCHERS
     You can watch for signals using a signal watcher, "signal" is the signal
-    *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked
+    *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
-    whenever a signal occurs.
+    callback to be invoked whenever a signal occurs.
     Although the callback might get passed parameters, their value and
     presence is undefined and you cannot rely on them. Portable AnyEvent
     callbacks cannot use arguments passed to signal watcher callbacks.
     an AnyEvent program, you *have* to create at least one watcher before
     you "fork" the child (alternatively, you can call "AnyEvent::detect").
     Example: fork a process and wait for it
-      my $done = AnyEvent->condvar;
+       my $done = AnyEvent->condvar;
-      my $pid = fork or exit 5;
+   my $pid = fork or exit 5;
-      my $w = AnyEvent->child (
+   my $w = AnyEvent->child (
-         pid => $pid,
+          pid => $pid,
-         cb  => sub {
+          cb  => sub {
-            my ($pid, $status) = @_;
+             my ($pid, $status) = @_;
-            warn "pid $pid exited with status $status";
+             warn "pid $pid exited with status $status";
-            $done->send;
+             $done->send;
-         },
+          },
-      );
+       );
-      # do something else, then wait for process exit
+   # do something else, then wait for process exit
-      $done->recv;
+       $done->recv;
   CONDITION VARIABLES
     If you are familiar with some event loops you will know that all of them
     require you to run some blocking "loop", "run" or similar function that
     will actively watch for new events and call your callbacks.
     "cb", which specifies a callback to be called when the condition
     variable becomes true.
     After creation, the condition variable is "false" until it becomes
     "true" by calling the "send" method (or calling the condition variable
-    as if it were a callback).
+    as if it were a callback, read about the caveats in the description for
+    the "->send" method).
     Condition variables are similar to callbacks, except that you can
     optionally wait for them. They can also be called merge points - points
     in time where multiple outstanding events have been processed. And yet
     another way to call them is transactions - each condition variable can
         Any arguments passed to the "send" call will be returned by all
         future "->recv" calls.
         Condition variables are overloaded so one can call them directly (as
         a code reference). Calling them directly is the same as calling
-        "send".
+        "send". Note, however, that many C-based event loops do not handle
+        overloading, so as tempting as it may be, passing a condition
+        variable instead of a callback does not work. Both the pure perl and
+        EV loops support overloading, however, as well as all functions that
+        use perl to invoke a callback (as in AnyEvent::Socket and
+        AnyEvent::DNS for example).
     $cv->croak ($error)
         Similar to send, but causes all call's to "->recv" to invoke
         "Carp::croak" with the given error message/object/scalar.
     $cb = $cv->cb ([new callback])
         This is a mutator function that returns the callback set and
         optionally replaces it before doing so.
         The callback will be called when the condition becomes "true", i.e.
-        when "send" or "croak" are called. Calling "recv" inside the
+        when "send" or "croak" are called, with the only argument being the
+        condition variable itself. Calling "recv" inside the callback or at
-        callback or at any later time is guaranteed not to block.
+        any later time is guaranteed not to block.
 GLOBAL VARIABLES AND FUNCTIONS
     $AnyEvent::MODEL
         Contains "undef" until the first watcher is being created. Then it
         contains the event model that is being used, which is the name of
     If it doesn't care, it can just "use AnyEvent" and use it itself, or not
     do anything special (it does not need to be event-based) and let
     AnyEvent decide which implementation to chose if some module relies on
     it.
-    If the main program relies on a specific event model. For example, in
+    If the main program relies on a specific event model - for example, in
-    Gtk2 programs you have to rely on the Glib module. You should load the
+    Gtk2 programs you have to rely on the Glib module - you should load the
     event module before loading AnyEvent or any module that uses it:
     generally speaking, you should load it as early as possible. The reason
     is that modules might create watchers when they are loaded, and AnyEvent
     will decide on the event model to use as soon as it creates watchers,
     and it might chose the wrong one unless you load the correct one
     yourself.
-    You can chose to use a rather inefficient pure-perl implementation by
+    You can chose to use a pure-perl implementation by loading the
-    loading the "AnyEvent::Impl::Perl" module, which gives you similar
+    "AnyEvent::Impl::Perl" module, which gives you similar behaviour
-    behaviour everywhere, but letting AnyEvent chose is generally better.
+    everywhere, but letting AnyEvent chose the model is generally better.
+  MAINLOOP EMULATION
+    Sometimes (often for short test scripts, or even standalone programs who
+    only want to use AnyEvent), you do not want to run a specific event
+    loop.
+    In that case, you can use a condition variable like this:
+       AnyEvent->condvar->recv;
+    This has the effect of entering the event loop and looping forever.
+    Note that usually your program has some exit condition, in which case it
+    is better to use the "traditional" approach of storing a condition
+    variable somewhere, waiting for it, and sending it when the program
+    should exit cleanly.
 OTHER MODULES
     The following is a non-exhaustive list of additional modules that use
     AnyEvent and can therefore be mixed easily with other AnyEvent modules
     in the same program. Some of the modules come with AnyEvent, some are
     AnyEvent::Util
         Contains various utility functions that replace often-used but
         blocking functions such as "inet_aton" by event-/callback-based
         versions.
-    AnyEvent::Handle
-        Provide read and write buffers and manages watchers for reads and
-        writes.
     AnyEvent::Socket
         Provides various utility functions for (internet protocol) sockets,
         addresses and name resolution. Also functions to create non-blocking
         tcp connections or tcp servers, with IPv6 and SRV record support and
         more.
+    AnyEvent::Handle
+        Provide read and write buffers, manages watchers for reads and
+        writes, supports raw and formatted I/O, I/O queued and fully
+        transparent and non-blocking SSL/TLS.
+    AnyEvent::DNS
+        Provides rich asynchronous DNS resolver capabilities.
+    AnyEvent::HTTP
+        A simple-to-use HTTP library that is capable of making a lot of
+        concurrent HTTP requests.
     AnyEvent::HTTPD
         Provides a simple web application server framework.
-    AnyEvent::DNS
-        Provides rich asynchronous DNS resolver capabilities.
     AnyEvent::FastPing
         The fastest ping in the west.
+    AnyEvent::DBI
+        Executes DBI requests asynchronously in a proxy process.
+    AnyEvent::AIO
+        Truly asynchronous I/O, should be in the toolbox of every event
+        programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
+        together.
+    AnyEvent::BDB
+        Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently
+        fuses BDB and AnyEvent together.
+    AnyEvent::GPSD
+        A non-blocking interface to gpsd, a daemon delivering GPS
+        information.
+    AnyEvent::IGS
+        A non-blocking interface to the Internet Go Server protocol (used by
+        App::IGS).
     Net::IRC3
         AnyEvent based IRC client module family.
     Net::XMPP2
     Event::ExecFlow
         High level API for event-based execution flow control.
     Coro
         Has special support for AnyEvent via Coro::AnyEvent.
-    AnyEvent::AIO, IO::AIO
-        Truly asynchronous I/O, should be in the toolbox of every event
-        programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent
-        together.
-    AnyEvent::BDB, BDB
-        Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently
-        fuses IO::AIO and AnyEvent together.
     IO::Lambda
         The lambda approach to I/O - don't ask, look there. Can use
         AnyEvent.
         conditions, such as not being able to load the event model specified
         by "PERL_ANYEVENT_MODEL".
         When set to 2 or higher, cause AnyEvent to report to STDERR which
         event model it chooses.
+    "PERL_ANYEVENT_STRICT"
+        AnyEvent does not do much argument checking by default, as thorough
+        argument checking is very costly. Setting this variable to a true
+        value will cause AnyEvent to load "AnyEvent::Strict" and then to
+        thoroughly check the arguments passed to most method calls. If it
+        finds any problems it will croak.
+        In other words, enables "strict" mode.
+        Unlike "use strict" it is definitely recommended ot keep it off in
+        production.
     "PERL_ANYEVENT_MODEL"
         This can be used to specify the event model to be used by AnyEvent,
         before auto detection and -probing kicks in. It must be a string
         consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
         This functionality might change in future versions.
         For example, to force the pure perl model (AnyEvent::Impl::Perl) you
         could start your program like this:
-          PERL_ANYEVENT_MODEL=Perl perl ...
+           PERL_ANYEVENT_MODEL=Perl perl ...
     "PERL_ANYEVENT_PROTOCOLS"
         Used by both AnyEvent::DNS and AnyEvent::Socket to determine
         preferences for IPv4 or IPv6. The default is unspecified (and might
         change, or be the result of auto probing).
         but some (broken) firewalls drop such DNS packets, which is why it
         is off by default.
         Setting this variable to 1 will cause AnyEvent::DNS to announce
         EDNS0 in its DNS requests.
+    "PERL_ANYEVENT_MAX_FORKS"
+        The maximum number of child processes that
+        "AnyEvent::Util::fork_call" will create in parallel.
 EXAMPLE PROGRAM
     The following program uses an I/O watcher to read data from STDIN, a
     timer to display a message once per second, and a condition variable to
     quit the program when the user enters quit:
     model than specified in the variable.
     You can make AnyEvent completely ignore this variable by deleting it
     before the first watcher gets created, e.g. with a "BEGIN" block:
-      BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
+       BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
-      use AnyEvent;
+   use AnyEvent;
     Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
     be used to probe what backend is used and gain other information (which
-    is probably even less useful to an attacker than PERL_ANYEVENT_MODEL).
+    is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
+    and $ENV{PERL_ANYEGENT_STRICT}.
+BUGS
+    Perl 5.8 has numerous memleaks that sometimes hit this module and are
+    hard to work around. If you suffer from memleaks, first upgrade to Perl
+    5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
+    annoying mamleaks, such as leaking on "map" and "grep" but it is usually
+    not as pronounced).
 SEE ALSO
     Utility functions: AnyEvent::Util.
     Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
     Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
     Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
 AUTHOR
-     Marc Lehmann <schmorp@schmorp.de>
+       Marc Lehmann <schmorp@schmorp.de>
-     http://home.schmorp.de/
+       http://home.schmorp.de/

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Comparing AnyEvent/README (file contents): Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC vs. Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.22 by root, Sat May 24 17:58:33 2008 UTC vs.
Revision 1.28 by root, Sat Jul 12 20:45:27 2008 UTC