--- AnyEvent/README 2012/04/13 09:57:41 1.70 +++ AnyEvent/README 2013/12/17 16:43:15 1.72 @@ -264,7 +264,7 @@ 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 @@ -471,6 +471,10 @@ 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 ( @@ -720,7 +724,7 @@ "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; @@ -738,6 +742,10 @@ $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 @@ -776,10 +784,15 @@ 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 detected. This condition can be slightly loosened by using - Coro::AnyEvent, which allows you to do a blocking "->recv" from any - thread that doesn't run the event loop itself. + is not allowed and the "recv" call will "croak" if such a condition + is detected. This requirement can be dropped by relying on + Coro::AnyEvent , which allows you to do a blocking "->recv" from any + 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 @@ -1084,22 +1097,22 @@ 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, @@ -1108,12 +1121,24 @@ (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 @@ -1124,16 +1149,13 @@ 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 - about it yet). + (I haven't used it myself, but it seems the biggest problem with it + 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. @@ -2003,6 +2025,15 @@ 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 @@ -2019,17 +2050,34 @@ 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 - start worker children from some kind of manage rprocess is usually + parent and child, which is almost never what you want. Using "exec" to + 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