[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.71 by root, Wed Aug 21 08:40:28 2013 UTC vs.
Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC

     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;
         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
         do just that in a portbale fashion, supporting inotify on GNU/Linux
         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
     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

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Comparing AnyEvent/README (file contents): Revision 1.71 by root, Wed Aug 21 08:40:28 2013 UTC vs. Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.71 by root, Wed Aug 21 08:40:28 2013 UTC vs.
Revision 1.72 by root, Tue Dec 17 16:43:15 2013 UTC