[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs.
Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC

-NAME
+=> NAME
     AnyEvent - provide framework for multiple event loops
     EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
     loops
     that isn't itself. 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
     those use one of the supported event loops. It is trivial to add new
     event loops 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 enourmous amount of code and strict rules you have
+    modules, you get an enormous amount of code and strict rules you have to
-    to follow. AnyEvent, on the other hand, is lean and up to the point, by
+    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 filehandle to watch, etc.
+    the callback to call, the file handle to watch, etc.
     These watchers are normal Perl objects with normal Perl lifetime. After
     creating a watcher it will immediately "watch" for events and invoke the
     callback when the event occurs (of course, only when the event model is
     in control).
     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
     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.
-    Multiple signal occurances can be clumped together into one callback
+    Multiple signal occurrences can be clumped together into one callback
-    invocation, and callback invocation will be synchronous. synchronous
+    invocation, and callback invocation will be synchronous. Synchronous
     means that it might take a while until the signal gets handled by the
-    process, but it is guarenteed not to interrupt any other callbacks.
+    process, but it is guaranteed not to interrupt any other callbacks.
     The main advantage of using these watchers is that you can share a
     signal between multiple watchers.
     This watcher might use %SIG, so programs overwriting those signals
     Condition variables can be created by calling the "AnyEvent->condvar"
     method, usually without arguments. The only argument pair allowed is
     "cb", which specifies a callback to be called when the condition
     variable becomes true.
-    After creation, the conditon variable is "false" until it 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, read about the caveats in the description for
-    by calling the "send" method.
+    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 outstandign events have been processed. And yet
+    in time where multiple outstanding events have been processed. And yet
-    another way to call them is transations - each condition variable can be
+    another way to call them is transactions - each condition variable can
-    used to represent a transaction, which finishes at some point and
+    be used to represent a transaction, which finishes at some point and
     delivers a result.
     Condition variables are very useful to signal that something has
     finished, for example, if you write a module that does asynchronous http
     requests, then a condition variable would be the ideal candidate to
     you can block your main program until an event occurs - for example, you
     could "->recv" in your main program until the user clicks the Quit
     button of your app, which would "->send" the "quit" event.
     Note that condition variables recurse into the event loop - if you have
-    two pieces of code that call "->recv" in a round-robbin fashion, you
+    two pieces of code that call "->recv" in a round-robin fashion, you
     lose. Therefore, condition variables are good to export to your caller,
     but you should avoid making a blocking wait yourself, at least in
     callbacks, as this asks for trouble.
     Condition variables are represented by hash refs in perl, and the keys
     There are two "sides" to a condition variable - the "producer side"
     which eventually calls "-> send", and the "consumer side", which waits
     for the send to occur.
-    Example:
+    Example: wait for a timer.
        # wait till the result is ready
        my $result_ready = AnyEvent->condvar;
        # do something such as adding a timer
        # this "blocks" (while handling events) till the callback
        # calls send
        $result_ready->recv;
+    Example: wait for a timer, but take advantage of the fact that condition
+    variables are also code references.
+       my $done = AnyEvent->condvar;
+       my $delay = AnyEvent->timer (after => 5, cb => $done);
+       $done->recv;
    METHODS FOR PRODUCERS
     These methods should only be used by the producing side, i.e. the
     code/module that eventually sends the signal. Note that it is also the
     producer side which creates the condvar in most cases, but it isn't
     uncommon for the consumer to create it as well.
         If a callback has been set on the condition variable, it is called
         immediately from within send.
         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". 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.
         (the loop doesn't execute once).
         This is the general pattern when you "fan out" into multiple
         subrequests: use an outer "begin"/"end" pair to set the callback and
         ensure "end" is called at least once, and then, for each subrequest
-        you start, call "begin" and for eahc subrequest you finish, call
+        you start, call "begin" and for each subrequest you finish, call
         "end".
    METHODS FOR CONSUMERS
     These methods should only be used by the consuming side, i.e. the code
     awaits the condition.
         (programs might want to do that to stay interactive), so *if you are
         using this from a module, never require a blocking wait*, but let
         the caller decide whether the call will block or not (for example,
         by coupling condition variables with some kind of request results
         and supporting callbacks so the caller knows that getting the result
-        will not block, while still suppporting blocking waits if the caller
+        will not block, while still supporting blocking waits if the caller
         so desires).
         Another reason *never* to "->recv" in a module is that you cannot
         sensibly have two "->recv"'s in parallel, as that would require
         multiple interpreters or coroutines/threads, none of which
     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::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::DNS
+        Provides rich asynchronous DNS resolver capabilities.
     AnyEvent::HTTPD
         Provides a simple web application server framework.
-    AnyEvent::DNS
-        Provides asynchronous DNS resolver capabilities, beyond what
-        AnyEvent::Util offers.
     AnyEvent::FastPing
         The fastest ping in the west.
     Net::IRC3
         When set to 2 or higher, cause AnyEvent to report to STDERR which
         event model it chooses.
     "PERL_ANYEVENT_MODEL"
         This can be used to specify the event model to be used by AnyEvent,
-        before autodetection and -probing kicks in. It must be a string
+        before auto detection and -probing kicks in. It must be a string
         consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
         gets prepended and the resulting module name is loaded and if the
         load was successful, used as event model. If it fails to load
-        AnyEvent will proceed with autodetection and -probing.
+        AnyEvent will proceed with auto detection and -probing.
         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_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).
+        Must be set to a comma-separated list of protocols or address
+        families, current supported: "ipv4" and "ipv6". Only protocols
+        mentioned will be used, and preference will be given to protocols
+        mentioned earlier in the list.
+        This variable can effectively be used for denial-of-service attacks
+        against local programs (e.g. when setuid), although the impact is
+        likely small, as the program has to handle connection errors
+        already-
+        Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
+        IPv6, but support both and try to use both.
+        "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
+        resolve or contact IPv6 addresses.
+        "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
+        prefer IPv6 over IPv4.
+    "PERL_ANYEVENT_EDNS0"
+        Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
+        for DNS. This extension is generally useful to reduce DNS traffic,
+        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:
        syswrite $txn->{fh}, $txn->{request}
           or die "connection or write error";
        $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
     Again, "fh_ready_r" waits till all data has arrived, and then stores the
-    result and signals any possible waiters that the request ahs finished:
+    result and signals any possible waiters that the request has finished:
        sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
        if (end-of-file or data complete) {
          $txn->{result} = $txn->{buf};
        $txn->{finished}->recv;
        return $txn->{result};
     The actual code goes further and collects all errors ("die"s,
-    exceptions) that occured during request processing. The "result" method
+    exceptions) that occurred during request processing. The "result" method
     detects whether an exception as thrown (it is stored inside the $txn
     object) and just throws the exception, which means connection errors and
     other problems get reported tot he code that tries to use the result,
     not in a random callback.
     over the event loops themselves and to give you an impression of the
     speed of various event loops I prepared some benchmarks.
   BENCHMARKING ANYEVENT OVERHEAD
     Here is a benchmark of various supported event models used natively and
-    through anyevent. The benchmark creates a lot of timers (with a zero
+    through AnyEvent. The benchmark creates a lot of timers (with a zero
     timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
     which it is), lets them fire exactly once and destroys them again.
     Source code for this benchmark is found as eg/bench in the AnyEvent
     distribution.
     *   You should avoid POE like the plague if you want performance or
         reasonable memory usage.
   BENCHMARKING THE LARGE SERVER CASE
-    This benchmark atcually benchmarks the event loop itself. It works by
+    This benchmark actually benchmarks the event loop itself. It works by
-    creating a number of "servers": each server consists of a socketpair, a
+    creating a number of "servers": each server consists of a socket pair, a
     timeout watcher that gets reset on activity (but never fires), and an
     I/O watcher waiting for input on one side of the socket. Each time the
     socket watcher reads a byte it will write that byte to a random other
     "server".
     The effect is that there will be a lot of I/O watchers, only part of
     which are active at any one point (so there is a constant number of
-    active fds for each loop iterstaion, but which fds these are is random).
+    active fds for each loop iteration, but which fds these are is random).
     The timeout is reset each time something is read because that reflects
     how most timeouts work (and puts extra pressure on the event loops).
-    In this benchmark, we use 10000 socketpairs (20000 sockets), of which
+    In this benchmark, we use 10000 socket pairs (20000 sockets), of which
     100 (1%) are active. This mirrors the activity of large servers with
     many connections, most of which are idle at any one point in time.
     Source code for this benchmark is found as eg/bench2 in the AnyEvent
     distribution.
    Explanation of the columns
     *sockets* is the number of sockets, and twice the number of "servers"
     (as each server has a read and write socket end).
-    *create* is the time it takes to create a socketpair (which is
+    *create* is the time it takes to create a socket pair (which is
     nontrivial) and two watchers: an I/O watcher and a timeout watcher.
     *request*, the most important value, is the time it takes to handle a
     single "request", that is, reading the token from the pipe and
     forwarding it to another server. This includes deleting the old timeout
     and speed most when you have lots of watchers, not when you only have a
     few of them).
     EV is again fastest.
-    Perl again comes second. It is noticably faster than the C-based event
+    Perl again comes second. It is noticeably faster than the C-based event
     loops Event and Glib, although the difference is too small to really
     matter.
     POE also performs much better in this case, but is is still far behind
     the others.
     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).
 SEE ALSO
+    Utility functions: AnyEvent::Util.
     Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk,
     Event::Lib, Qt, POE.
     Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
     AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
     AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE.
+    Non-blocking file handles, sockets, TCP clients and servers:
+    AnyEvent::Handle, AnyEvent::Socket.
+    Asynchronous DNS: AnyEvent::DNS.
     Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event,
-    Nontrivial usage examples: Net::FCP, Net::XMPP2.
+    Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS.
 AUTHOR
      Marc Lehmann <schmorp@schmorp.de>
      http://home.schmorp.de/

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Comparing AnyEvent/README (file contents): Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs. Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.21 by root, Sat May 17 21:34:15 2008 UTC vs.
Revision 1.24 by root, Thu May 29 03:46:04 2008 UTC