[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.68 by root, Fri Aug 26 18:09:04 2011 UTC vs.
Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC

     Example 2: fire an event after 0.5 seconds, then roughly every second.
        my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
           warn "timeout\n";
-       };
+       });
    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").
     will not restart syscalls (that includes Async::Interrupt and AnyEvent's
     pure perl implementation).
    Safe/Unsafe Signals
     Perl signals can be either "safe" (synchronous to opcode handling) or
-    "unsafe" (asynchronous) - the former might get delayed indefinitely, the
+    "unsafe" (asynchronous) - the former might delay signal delivery
-    latter might corrupt your memory.
+    indefinitely, the latter might corrupt your memory.
     AnyEvent signal handlers are, in addition, synchronous to the event
     loop, i.e. they will not interrupt your running perl program but will
     only be called as part of the normal event handling (just like timer,
     I/O etc. callbacks, too).
    Signal Races, Delays and Workarounds
     Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
     callbacks to signals in a generic way, which is a pity, as you cannot do
     race-free signal handling in perl, requiring C libraries for this.
     AnyEvent will try to do its best, which means in some cases, signals
-    will be delayed. The maximum time a signal might be delayed is specified
+    will be delayed. The maximum time a signal might be delayed is 10
-    in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable
+    seconds by default, but can be overriden via
-    can be changed only before the first signal watcher is created, and
+    $ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
-    should be left alone otherwise. This variable determines how often
+    - see the "ENVIRONMENT VARIABLES" section for details.
-    AnyEvent polls for signals (in case a wake-up was missed). Higher values
-    will cause fewer spurious wake-ups, which is better for power and CPU
-    saving.
     All these problems can be avoided by installing the optional
     Async::Interrupt module, which works with most event loops. It will not
     work with inherently broken event loops such as Event or Event::Lib (and
-    not with POE currently, as POE does its own workaround with one-second
-    latency). For those, you just have to suffer the delays.
+    not with POE currently). For those, you just have to suffer the delays.
   CHILD PROCESS WATCHERS
        $w = AnyEvent->child (pid => <process id>, cb => <callback>);
     You can also watch for a child process exit and catch its exit status.
     Example: fork a process and wait for it
        my $done = AnyEvent->condvar;
+       # this forks and immediately calls exit in the child. this
+       # normally has all sorts of bad consequences for your parent,
+       # so take this as an example only. always fork and exec,
+       # or call POSIX::_exit, in real code.
        my $pid = fork or exit 5;
        my $w = AnyEvent->child (
           pid => $pid,
           cb  => sub {
         This works because for every event source (EOF on file handle),
         there is one call to "begin", so the condvar waits for all calls to
         "end" before sending.
         The ping example mentioned above is slightly more complicated, as
-        the there are results to be passwd back, and the number of tasks
+        the there are results to be passed back, and the number of tasks
         that are begun can potentially be zero:
            my $cv = AnyEvent->condvar;
            my %result;
               };
            }
            $cv->end;
+           ...
+           my $results = $cv->recv;
         This code fragment supposedly pings a number of hosts and calls
         "send" after results for all then have have been gathered - in any
         order. To achieve this, the code issues a call to "begin" when it
         starts each ping request and calls "end" when it has received some
         result for it. Since "begin" and "end" only maintain a counter, the
         In list context, all parameters passed to "send" will be returned,
         in scalar context only the first one will be returned.
         Note that doing a blocking wait in a callback is not supported by
         any event loop, that is, recursive invocation of a blocking "->recv"
-        is not allowed, and the "recv" call will "croak" if such a condition
+        is not allowed and the "recv" call will "croak" if such a condition
-        is detected. This condition can be slightly loosened by using
+        is detected. This requirement can be dropped by relying on
-        Coro::AnyEvent, which allows you to do a blocking "->recv" from any
+        Coro::AnyEvent , which allows you to do a blocking "->recv" from any
-        thread that doesn't run the event loop itself.
+        thread that doesn't run the event loop itself. Coro::AnyEvent is
+        loaded automatically when Coro is used with AnyEvent, so code does
+        not need to do anything special to take advantage of that: any code
+        that would normally block your program because it calls "recv", be
+        executed in an "async" thread instead without blocking other
+        threads.
         Not all event models support a blocking wait - some die in that case
         (programs might want to do that to stay interactive), so *if you are
         using this from a module, never require a blocking wait*. Instead,
         let the caller decide whether the call will block or not (for
         If AnyEvent::Log is not loaded then this function makes a simple
         test to see whether the message will be logged. If the test succeeds
         it will load AnyEvent::Log and call "AnyEvent::Log::log" -
         consequently, look at the AnyEvent::Log documentation for details.
-        If the test fails it will simply return.
+        If the test fails it will simply return. Right now this happens when
+        a numerical loglevel is used and it is larger than the level
+        specified via $ENV{PERL_ANYEVENT_VERBOSE}.
         If you want to sprinkle loads of logging calls around your code,
         consider creating a logger callback with the "AnyEvent::Log::logger"
         function, which can reduce typing, codesize and can reduce the
         logging overhead enourmously.
     modules come as part of AnyEvent, the others are available via CPAN (see
     <http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
     non-exhaustive list), and the list is heavily biased towards modules of
     the AnyEvent author himself :)
-    AnyEvent::Util
+    AnyEvent::Util (part of the AnyEvent distribution)
         Contains various utility functions that replace often-used blocking
         functions such as "inet_aton" with event/callback-based versions.
-    AnyEvent::Socket
+    AnyEvent::Socket (part of the AnyEvent distribution)
         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
+    AnyEvent::Handle (part of the AnyEvent distribution)
         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 (via AnyEvent::TLS).
-    AnyEvent::DNS
+    AnyEvent::DNS (part of the AnyEvent distribution)
         Provides rich asynchronous DNS resolver capabilities.
     AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
     AnyEvent::IGS, AnyEvent::FCP
         Implement event-based interfaces to the protocols of the same name
         (for the curious, IGS is the International Go Server and FCP is the
         Freenet Client Protocol).
-    AnyEvent::AIO
+    AnyEvent::AIO (part of the AnyEvent distribution)
         Truly asynchronous (as opposed to non-blocking) I/O, should be in
         the toolbox of every event programmer. AnyEvent::AIO transparently
         fuses IO::AIO and AnyEvent together, giving AnyEvent access to
         event-based file I/O, and much more.
+    AnyEvent::Fork, AnyEvent::Fork::RPC, AnyEvent::Fork::Pool,
+    AnyEvent::Fork::Remote
+        These let you safely fork new subprocesses, either locally or
+        remotely (e.g.v ia ssh), using some RPC protocol or not, without the
+        limitations normally imposed by fork (AnyEvent works fine for
+        example). Dynamically-resized worker pools are obviously included as
+        well.
+        And they are quite tiny and fast as well - "abusing" AnyEvent::Fork
+        just to exec external programs can easily beat using "fork" and
+        "exec" (or even "system") in most programs.
     AnyEvent::Filesys::Notify
         AnyEvent is good for non-blocking stuff, but it can't detect file or
         path changes (e.g. "watch this directory for new files", "watch this
         file for changes"). The AnyEvent::Filesys::Notify module promises to
         and some weird, without doubt broken, stuff on OS X to monitor
         files. It can fall back to blocking scans at regular intervals
         transparently on other platforms, so it's about as portable as it
         gets.
-        (I haven't used it myself, but I haven't heard anybody complaining
+        (I haven't used it myself, but it seems the biggest problem with it
-        about it yet).
+        is it quite bad performance).
     AnyEvent::DBI
         Executes DBI requests asynchronously in a proxy process for you,
         notifying you in an event-based way when the operation is finished.
-    AnyEvent::HTTPD
-        A simple embedded webserver.
     AnyEvent::FastPing
         The fastest ping in the west.
     Coro
     This ensures that child processes will not see the "AE_" variables.
     The following environment variables are currently known to AnyEvent:
     "PERL_ANYEVENT_VERBOSE"
-        By default, AnyEvent will be completely silent except in fatal
+        By default, AnyEvent will log messages with loglevel 4 ("error") or
-        conditions. You can set this environment variable to make AnyEvent
+        higher (see AnyEvent::Log). You can set this environment variable to
-        more talkative. If you want to do more than just set the global
+        a numerical loglevel to make AnyEvent more (or less) talkative.
+        If you want to do more than just set the global logging level you
-        logging level you should have a look at "PERL_ANYEVENT_LOG", which
+        should have a look at "PERL_ANYEVENT_LOG", which allows much more
-        allows much more complex specifications.
+        complex specifications.
+        When set to 0 ("off"), then no messages whatsoever will be logged
+        with everything else at defaults.
-        When set to 5 or higher (warn), causes AnyEvent to warn about
+        When set to 5 or higher ("warn"), AnyEvent warns about unexpected
-        unexpected conditions, such as not being able to load the event
+        conditions, such as not being able to load the event model specified
-        model specified by "PERL_ANYEVENT_MODEL", or a guard callback
+        by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
-        throwing an exception - this is the minimum recommended level.
+        - this is the minimum recommended level for use during development.
-        When set to 7 or higher (info), cause AnyEvent to report which event
+        When set to 7 or higher (info), AnyEvent reports which event model
-        model it chooses.
+        it chooses.
         When set to 8 or higher (debug), then AnyEvent will report extra
         information on which optional modules it loads and how it implements
         certain features.
         itself.
         Note that specifying this environment variable causes the
         AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
         does not, so only using the latter saves a few hundred kB of memory
-        until the first message is being logged.
+        unless a module explicitly needs the extra features of
+        AnyEvent::Log.
     "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
         is definitely recommended to keep it off in production. Keeping
         "PERL_ANYEVENT_STRICT=1" in your environment while developing
         programs can be very useful, however.
     "PERL_ANYEVENT_DEBUG_SHELL"
-        If this env variable is set, then its contents will be interpreted
+        If this env variable is nonempty, then its contents will be
-        by "AnyEvent::Socket::parse_hostport" (after replacing every
+        interpreted by "AnyEvent::Socket::parse_hostport" and
-        occurance of $$ by the process pid) and an "AnyEvent::Debug::shell"
+        "AnyEvent::Debug::shell" (after replacing every occurance of $$ by
-        is bound on that port. The shell object is saved in
+        the process pid). The shell object is saved in
         $AnyEvent::Debug::SHELL.
         This happens when the first watcher is created.
         For example, to bind a debug shell on a unix domain socket in
         /tmp/debug<pid>.sock, you could use this:
            PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
+           # connect with e.g.: socat readline /tmp/debug123.sock
+        Or to bind to tcp port 4545 on localhost:
+           PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
+           # connect with e.g.: telnet localhost 4545
-        Note that creating sockets in /tmp is very unsafe on multiuser
+        Note that creating sockets in /tmp or on localhost is very unsafe on
-        systems.
+        multiuser systems.
     "PERL_ANYEVENT_DEBUG_WRAP"
         Can be set to 0, 1 or 2 and enables wrapping of all watchers for
         debugging purposes. See "AnyEvent::Debug::wrap" for details.
         For example, to force the pure perl model (AnyEvent::Loop::Perl) you
         could start your program like this:
            PERL_ANYEVENT_MODEL=Perl perl ...
+    "PERL_ANYEVENT_IO_MODEL"
+        The current file I/O model - see AnyEvent::IO for more info.
+        At the moment, only "Perl" (small, pure-perl, synchronous) and
+        "IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
+        if AnyEvent::AIO can be loaded, otherwise it is "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).
     "PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
         The default value for the "max_outstanding" parameter for the
         default DNS resolver - this is the maximum number of parallel DNS
         requests that are sent to the DNS server.
+    "PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
+        Perl has inherently racy signal handling (you can basically choose
+        between losing signals and memory corruption) - pure perl event
+        loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
+        available) therefore have to poll regularly to avoid losing signals.
+        Some event loops are racy, but don't poll regularly, and some event
+        loops are written in C but are still racy. For those event loops,
+        AnyEvent installs a timer that regularly wakes up the event loop.
+        By default, the interval for this timer is 10 seconds, but you can
+        override this delay with this environment variable (or by setting
+        the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
+        watchers).
+        Lower values increase CPU (and energy) usage, higher values can
+        introduce long delays when reaping children or waiting for signals.
+        The AnyEvent::Async module, if available, will be used to avoid this
+        polling (with most event loops).
     "PERL_ANYEVENT_RESOLV_CONF"
         The absolute path to a resolv.conf-style file to use instead of
         /etc/resolv.conf (or the OS-specific configuration) in the default
         resolver, or the empty string to select the default configuration.
         This module is part of perl since release 5.008. It will be used
         when the chosen event library does not come with a timing source of
         its own. The pure-perl event loop (AnyEvent::Loop) will additionally
         load it to try to use a monotonic clock for timing stability.
+    AnyEvent::AIO (and IO::AIO)
+        The default implementation of AnyEvent::IO is to do I/O
+        synchronously, stopping programs while they access the disk, which
+        is fine for a lot of programs.
+        Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
+        switch to a true asynchronous implementation, so event processing
+        can continue even while waiting for disk I/O.
 FORK
     Most event libraries are not fork-safe. The ones who are usually are
     because they rely on inefficient but fork-safe "select" or "poll" calls
     - higher performance APIs such as BSD's kqueue or the dreaded Linux
     epoll are usually badly thought-out hacks that are incompatible with
     usually happens when the first AnyEvent watcher is created, or the
     library is loaded).
     If you have to fork, you must either do so *before* creating your first
     watcher OR you must not use AnyEvent at all in the child OR you must do
-    something completely out of the scope of AnyEvent.
+    something completely out of the scope of AnyEvent (see below).
     The problem of doing event processing in the parent *and* the child is
     much more complicated: even for backends that *are* fork-aware or
     fork-safe, their behaviour is not usually what you want: fork clones all
     watchers, that means all timers, I/O watchers etc. are active in both
-    parent and child, which is almost never what you want. USing "exec" to
+    parent and child, which is almost never what you want. Using "exec" to
-    start worker children from some kind of manage rprocess is usually
+    start worker children from some kind of manage prrocess is usually
     preferred, because it is much easier and cleaner, at the expense of
     having to have another binary.
+    In addition to logical problems with fork, there are also implementation
+    problems. For example, on POSIX systems, you cannot fork at all in Perl
+    code if a thread (I am talking of pthreads here) was ever created in the
+    process, and this is just the tip of the iceberg. In general, using fork
+    from Perl is difficult, and attempting to use fork without an exec to
+    implement some kind of parallel processing is almost certainly doomed.
+    To safely fork and exec, you should use a module such as Proc::FastSpawn
+    that let's you safely fork and exec new processes.
+    If you want to do multiprocessing using processes, you can look at the
+    AnyEvent::Fork module (and some related modules such as
+    AnyEvent::Fork::RPC, AnyEvent::Fork::Pool and AnyEvent::Fork::Remote).
+    This module allows you to safely create subprocesses without any
+    limitations - you can use X11 toolkits or AnyEvent in the children
+    created by AnyEvent::Fork safely and without any special precautions.
 SECURITY CONSIDERATIONS
     AnyEvent can be forced to load any event model via
     $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
     to execute arbitrary code or directly gain access, it can easily be used
     AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
     Non-blocking handles, pipes, stream sockets, TCP clients and servers:
     AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
+    Asynchronous File I/O: AnyEvent::IO.
     Asynchronous DNS: AnyEvent::DNS.
     Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
     Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
     AnyEvent::HTTP.
 AUTHOR
        Marc Lehmann <schmorp@schmorp.de>
-       http://home.schmorp.de/
+       http://anyevent.schmorp.de

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Comparing AnyEvent/README (file contents): Revision 1.68 by root, Fri Aug 26 18:09:04 2011 UTC vs. Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.68 by root, Fri Aug 26 18:09:04 2011 UTC vs.
Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC