Provided by: libio-async-perl_0.71-1_all 
NAME
"IO::Async::Loop" - core loop of the "IO::Async" framework
SYNOPSIS
use IO::Async::Stream;
use IO::Async::Timer::Countdown;
use IO::Async::Loop;
my $loop = IO::Async::Loop->new;
$loop->add( IO::Async::Timer::Countdown->new(
delay => 10,
on_expire => sub { print "10 seconds have passed\n" },
)->start );
$loop->add( IO::Async::Stream->new_for_stdin(
on_read => sub {
my ( $self, $buffref, $eof ) = @_;
while( $$buffref =~ s/^(.*)\n// ) {
print "You typed a line $1\n";
}
return 0;
},
) );
$loop->run;
DESCRIPTION
This module provides an abstract class which implements the core loop of the IO::Async
framework. Its primary purpose is to store a set of IO::Async::Notifier objects or
subclasses of them. It handles all of the lower-level set manipulation actions, and leaves
the actual IO readiness testing/notification to the concrete class that implements it. It
also provides other functionality such as signal handling, child process managing, and
timers.
See also the two bundled Loop subclasses:
IO::Async::Loop::Select
IO::Async::Loop::Poll
Or other subclasses that may appear on CPAN which are not part of the core IO::Async
distribution.
Ignoring SIGPIPE
Since version 0.66 loading this module automatically ignores "SIGPIPE", as it is highly
unlikely that the default-terminate action is the best course of action for an
IO::Async-based program to take. If at load time the handler disposition is still set as
"DEFAULT", it is set to ignore. If already another handler has been placed there by the
program code, it will be left undisturbed.
MAGIC CONSTRUCTOR
new
$loop = IO::Async::Loop->new
This function attempts to find a good subclass to use, then calls its constructor. It
works by making a list of likely candidate classes, then trying each one in turn,
"require"ing the module then calling its "new" method. If either of these operations
fails, the next subclass is tried. If no class was successful, then an exception is
thrown.
The constructed object is cached, and will be returned again by a subsequent call. The
cache will also be set by a constructor on a specific subclass. This behaviour makes it
possible to simply use the normal constructor in a module that wishes to interract with
the main program's Loop, such as an integration module for another event system.
For example, the following two $loop variables will refer to the same object:
use IO::Async::Loop;
use IO::Async::Loop::Poll;
my $loop_poll = IO::Async::Loop::Poll->new;
my $loop = IO::Async::Loop->new;
While it is not advised to do so under normal circumstances, if the program really wishes
to construct more than one Loop object, it can call the constructor "really_new", or
invoke one of the subclass-specific constructors directly.
The list of candidates is formed from the following choices, in this order:
• $ENV{IO_ASYNC_LOOP}
If this environment variable is set, it should contain a comma-separated list of
subclass names. These names may or may not be fully-qualified; if a name does not
contain "::" then it will have "IO::Async::Loop::" prepended to it. This allows the
end-user to specify a particular choice to fit the needs of his use of a program using
IO::Async.
• $IO::Async::Loop::LOOP
If this scalar is set, it should contain a comma-separated list of subclass names.
These may or may not be fully-qualified, as with the above case. This allows a program
author to suggest a loop module to use.
In cases where the module subclass is a hard requirement, such as GTK programs using
"Glib", it would be better to use the module specifically and invoke its constructor
directly.
• IO::Async::OS->LOOP_PREFER_CLASSES
The IO::Async::OS hints module for the given OS is then consulted to see if it
suggests any other module classes specific to the given operating system.
• $^O
The module called "IO::Async::Loop::$^O" is tried next. This allows specific OSes,
such as the ever-tricky "MSWin32", to provide an implementation that might be more
efficient than the generic ones, or even work at all.
This option is now discouraged in favour of the IO::Async::OS hint instead. At some
future point it may be removed entirely, given as currently only "linux" uses it.
• Poll and Select
Finally, if no other choice has been made by now, the built-in "Poll" module is
chosen. This should always work, but in case it doesn't, the "Select" module will be
chosen afterwards as a last-case attempt. If this also fails, then the magic
constructor itself will throw an exception.
If any of the explicitly-requested loop types ($ENV{IO_ASYNC_LOOP} or
$IO::Async::Loop::LOOP) fails to load then a warning is printed detailing the error.
Implementors of new "IO::Async::Loop" subclasses should see the notes about "API_VERSION"
below.
NOTIFIER MANAGEMENT
The following methods manage the collection of IO::Async::Notifier objects.
add
$loop->add( $notifier )
This method adds another notifier object to the stored collection. The object may be a
IO::Async::Notifier, or any subclass of it.
When a notifier is added, any children it has are also added, recursively. In this way,
entire sections of a program may be written within a tree of notifier objects, and added
or removed on one piece.
remove
$loop->remove( $notifier )
This method removes a notifier object from the stored collection, and recursively and
children notifiers it contains.
notifiers
@notifiers = $loop->notifiers
Returns a list of all the notifier objects currently stored in the Loop.
LOOPING CONTROL
The following methods control the actual run cycle of the loop, and hence the program.
loop_once
$count = $loop->loop_once( $timeout )
This method performs a single wait loop using the specific subclass's underlying
mechanism. If $timeout is undef, then no timeout is applied, and it will wait until an
event occurs. The intention of the return value is to indicate the number of callbacks
that this loop executed, though different subclasses vary in how accurately they can
report this. See the documentation for this method in the specific subclass for more
information.
run
@result = $loop->run
$result = $loop->run
Runs the actual IO event loop. This method blocks until the "stop" method is called, and
returns the result that was passed to "stop". In scalar context only the first result is
returned; the others will be discarded if more than one value was provided. This method
may be called recursively.
This method is a recent addition and may not be supported by all the "IO::Async::Loop"
subclasses currently available on CPAN.
stop
$loop->stop( @result )
Stops the inner-most "run" method currently in progress, causing it to return the given
@result.
This method is a recent addition and may not be supported by all the "IO::Async::Loop"
subclasses currently available on CPAN.
loop_forever
$loop->loop_forever
A synonym for "run", though this method does not return a result.
loop_stop
$loop->loop_stop
A synonym for "stop", though this method does not pass any results.
post_fork
$loop->post_fork
The base implementation of this method does nothing. It is provided in case some Loop
subclasses should take special measures after a "fork()" system call if the main body of
the program should survive in both running processes.
This may be required, for example, in a long-running server daemon that forks multiple
copies on startup after opening initial listening sockets. A loop implementation that uses
some in-kernel resource that becomes shared after forking (for example, a Linux "epoll" or
a BSD "kqueue" filehandle) would need recreating in the new child process before the
program can continue.
FUTURE SUPPORT
The following methods relate to IO::Async::Future objects.
new_future
$future = $loop->new_future
Returns a new IO::Async::Future instance with a reference to the Loop.
await
$loop->await( $future )
Blocks until the given future is ready, as indicated by its "is_ready" method. As a
convenience it returns the future, to simplify code:
my @result = $loop->await( $future )->get;
await_all
$loop->await_all( @futures )
Blocks until all the given futures are ready, as indicated by the "is_ready" method.
Equivalent to calling "await" on a "Future->wait_all" except that it doesn't create the
surrounding future object.
delay_future
$loop->delay_future( %args )->get
Returns a new IO::Async::Future instance which will become done at a given point in time.
The %args should contain an "at" or "after" key as per the "watch_time" method. The
returned future may be cancelled to cancel the timer. At the alloted time the future will
succeed with an empty result list.
timeout_future
$loop->timeout_future( %args )->get
Returns a new IO::Async::Future instance which will fail at a given point in time. The
%args should contain an "at" or "after" key as per the "watch_time" method. The returned
future may be cancelled to cancel the timer. At the alloted time, the future will fail
with the string "Timeout".
FEATURES
Most of the following methods are higher-level wrappers around base functionality provided
by the low-level API documented below. They may be used by IO::Async::Notifier subclasses
or called directly by the program.
The following methods documented with a trailing call to "->get" return Future instances.
attach_signal
$id = $loop->attach_signal( $signal, $code )
This method adds a new signal handler to watch the given signal. The same signal can be
attached to multiple times; its callback functions will all be invoked, in no particular
order.
The returned $id value can be used to identify the signal handler in case it needs to be
removed by the "detach_signal" method. Note that this value may be an object reference, so
if it is stored, it should be released after it cancelled, so the object itself can be
freed.
$signal The name of the signal to attach to. This should be a bare name like "TERM".
$code A CODE reference to the handling callback.
Attaching to "SIGCHLD" is not recommended because of the way all child processes use it to
report their termination. Instead, the "watch_child" method should be used to watch for
termination of a given child process. A warning will be printed if "SIGCHLD" is passed
here, but in future versions of IO::Async this behaviour may be disallowed altogether.
See also POSIX for the "SIGname" constants.
For a more flexible way to use signals from within Notifiers, see instead the
IO::Async::Signal object.
detach_signal
$loop->detach_signal( $signal, $id )
Removes a previously-attached signal handler.
$signal The name of the signal to remove from. This should be a bare name like "TERM".
$id The value returned by the "attach_signal" method.
later
$loop->later( $code )
Schedules a code reference to be invoked as soon as the current round of IO operations is
complete.
The code reference is never invoked immediately, though the loop will not perform any
blocking operations between when it is installed and when it is invoked. It may call
"select", "poll" or equivalent with a zero-second timeout, and process any currently-
pending IO conditions before the code is invoked, but it will not block for a non-zero
amount of time.
This method is implemented using the "watch_idle" method, with the "when" parameter set to
"later". It will return an ID value that can be passed to "unwatch_idle" if required.
spawn_child
$loop->spawn_child( %params )
This method creates a new child process to run a given code block or command. For more
detail, see the "spawn_child" method on the IO::Async::ChildManager class.
open_child
$pid = $loop->open_child( %params )
This creates a new child process to run the given code block or command, and attaches
filehandles to it that the parent will watch. This method is a light wrapper around
constructing a new IO::Async::Process object, provided largely for backward compatibility.
New code ought to construct such an object directly, as it may provide more features than
are available here.
The %params hash takes the following keys:
command => ARRAY or STRING
code => CODE
The command or code to run in the child process (as per the "spawn" method)
on_finish => CODE
A continuation to be called when the child process exits and has closed all of the
filehandles that were set up for it. It will be invoked in the following way:
$on_finish->( $pid, $exitcode )
The second argument is passed the plain perl $? value.
on_error => CODE
Optional continuation to be called when the child code block throws an exception,
or the command could not be exec(2)ed. It will be invoked in the following way (as
per "spawn")
$on_error->( $pid, $exitcode, $dollarbang, $dollarat )
If this continuation is not supplied, then "on_finish" is used instead. The value
of $! and $@ will not be reported.
setup => ARRAY
Optional reference to an array to pass to the underlying "spawn" method.
In addition, the hash takes keys that define how to set up file descriptors in the child
process. (If the "setup" array is also given, these operations will be performed after
those specified by "setup".)
fdn => HASH
A hash describing how to set up file descriptor n. The hash may contain one of the
following sets of keys:
on_read => CODE
The child will be given the writing end of a pipe. The reading end will be
wrapped by an IO::Async::Stream using this "on_read" callback function.
from => STRING
The child will be given the reading end of a pipe. The string given by the
"from" parameter will be written to the child. When all of the data has been
written the pipe will be closed.
stdin => ...
stdout => ...
stderr => ...
Shortcuts for "fd0", "fd1" and "fd2" respectively.
run_child
$pid = $loop->run_child( %params )
This creates a new child process to run the given code block or command, capturing its
STDOUT and STDERR streams. When the process exits, a continuation is invoked being passed
the exitcode, and content of the streams.
command => ARRAY or STRING
code => CODE
The command or code to run in the child process (as per the "spawn_child" method)
on_finish => CODE
A continuation to be called when the child process exits and closed its STDOUT and
STDERR streams. It will be invoked in the following way:
$on_finish->( $pid, $exitcode, $stdout, $stderr )
The second argument is passed the plain perl $? value.
stdin => STRING
Optional. String to pass in to the child process's STDIN stream.
setup => ARRAY
Optional reference to an array to pass to the underlying "spawn" method.
This method is intended mainly as an IO::Async-compatible replacement for the perl
"readpipe" function (`backticks`), allowing it to replace
my $output = `command here`;
with
$loop->run_child(
command => "command here",
on_finish => sub {
my ( undef, $exitcode, $output ) = @_;
...
}
);
resolver
$loop->resolver
Returns the internally-stored IO::Async::Resolver object, used for name resolution
operations by the "resolve", "connect" and "listen" methods.
set_resolver
$loop->set_resolver( $resolver )
Sets the internally-stored IO::Async::Resolver object. In most cases this method should
not be required, but it may be used to provide an alternative resolver for special use-
cases.
resolve
@result = $loop->resolve( %params )->get
This method performs a single name resolution operation. It uses an internally-stored
IO::Async::Resolver object. For more detail, see the "resolve" method on the
IO::Async::Resolver class.
connect
$handle|$socket = $loop->connect( %params )->get
This method performs a non-blocking connection to a given address or set of addresses,
returning a IO::Async::Future which represents the operation. On completion, the future
will yield the connected socket handle, or the given IO::Async::Handle object.
There are two modes of operation. Firstly, a list of addresses can be provided which will
be tried in turn. Alternatively as a convenience, if a host and service name are provided
instead of a list of addresses, these will be resolved using the underlying loop's
"resolve" method into the list of addresses.
When attempting to connect to any among a list of addresses, there may be failures among
the first attempts, before a valid connection is made. For example, the resolver may have
returned some IPv6 addresses, but only IPv4 routes are valid on the system. In this case,
the first connect(2) syscall will fail. This isn't yet a fatal error, if there are more
addresses to try, perhaps some IPv4 ones.
For this reason, it is possible that the operation eventually succeeds even though some
system calls initially fail. To be aware of individual failures, the optional "on_fail"
callback can be used. This will be invoked on each individual socket(2) or connect(2)
failure, which may be useful for debugging or logging.
Because this module simply uses the "getaddrinfo" resolver, it will be fully IPv6-aware if
the underlying platform's resolver is. This allows programs to be fully IPv6-capable.
In plain address mode, the %params hash takes the following keys:
addrs => ARRAY
Reference to an array of (possibly-multiple) address structures to attempt to
connect to. Each should be in the layout described for "addr". Such a layout is
returned by the "getaddrinfo" named resolver.
addr => HASH or ARRAY
Shortcut for passing a single address to connect to; it may be passed directly
with this key, instead of in another array on its own. This should be in a format
recognised by IO::Async::OS's "extract_addrinfo" method.
This example shows how to use the "Socket" functions to construct one for TCP port
8001 on address 10.0.0.1:
$loop->connect(
addr => {
family => "inet",
socktype => "stream",
port => 8001,
ip => "10.0.0.1",
},
...
);
This example shows another way to connect to a UNIX socket at echo.sock.
$loop->connect(
addr => {
family => "unix",
socktype => "stream",
path => "echo.sock",
},
...
);
local_addrs => ARRAY
local_addr => HASH or ARRAY
Optional. Similar to the "addrs" or "addr" parameters, these specify a local
address or set of addresses to bind(2) the socket to before connect(2)ing it.
When performing the resolution step too, the "addrs" or "addr" keys are ignored, and
instead the following keys are taken:
host => STRING
service => STRING
The hostname and service name to connect to.
local_host => STRING
local_service => STRING
Optional. The hostname and/or service name to bind(2) the socket to locally before
connecting to the peer.
family => INT
socktype => INT
protocol => INT
flags => INT
Optional. Other arguments to pass along with "host" and "service" to the
"getaddrinfo" call.
socktype => STRING
Optionally may instead be one of the values 'stream', 'dgram' or 'raw' to stand
for "SOCK_STREAM", "SOCK_DGRAM" or "SOCK_RAW". This utility is provided to allow
the caller to avoid a separate "use Socket" only for importing these constants.
It is necessary to pass the "socktype" hint to the resolver when resolving the
host/service names into an address, as some OS's "getaddrinfo" functions require this
hint. A warning is emitted if neither "socktype" nor "protocol" hint is defined when
performing a "getaddrinfo" lookup. To avoid this warning while still specifying no
particular "socktype" hint (perhaps to invoke some OS-specific behaviour), pass 0 as the
"socktype" value.
In either case, it also accepts the following arguments:
handle => IO::Async::Handle
Optional. If given a IO::Async::Handle object or a subclass (such as
IO::Async::Stream or IO::Async::Socket its handle will be set to the newly-
connected socket on success, and that handle used as the result of the future
instead.
on_fail => CODE
Optional. After an individual socket(2) or connect(2) syscall has failed, this
callback is invoked to inform of the error. It is passed the name of the syscall
that failed, the arguments that were passed to it, and the error it generated.
I.e.
$on_fail->( "socket", $family, $socktype, $protocol, $! );
$on_fail->( "bind", $sock, $address, $! );
$on_fail->( "connect", $sock, $address, $! );
Because of the "try all" nature when given a list of multiple addresses, this
callback may be invoked multiple times, even before an eventual success.
This method accepts an "extensions" parameter; see the "EXTENSIONS" section below.
connect (void)
$loop->connect( %params )
When not returning a future, additional parameters can be given containing the
continuations to invoke on success or failure.
on_connected => CODE
A continuation that is invoked on a successful connect(2) call to a valid socket.
It will be passed the connected socket handle, as an "IO::Socket" object.
$on_connected->( $handle )
on_stream => CODE
An alternative to "on_connected", a continuation that is passed an instance of
IO::Async::Stream when the socket is connected. This is provided as a convenience
for the common case that a Stream object is required as the transport for a
Protocol object.
$on_stream->( $stream )
on_socket => CODE
Similar to "on_stream", but constructs an instance of IO::Async::Socket. This is
most useful for "SOCK_DGRAM" or "SOCK_RAW" sockets.
$on_socket->( $socket )
on_connect_error => CODE
A continuation that is invoked after all of the addresses have been tried, and
none of them succeeded. It will be passed the most significant error that
occurred, and the name of the operation it occurred in. Errors from the connect(2)
syscall are considered most significant, then bind(2), then finally socket(2).
$on_connect_error->( $syscall, $! )
on_resolve_error => CODE
A continuation that is invoked when the name resolution attempt fails. This is
invoked in the same way as the "on_error" continuation for the "resolve" method.
listen
$listener = $loop->listen( %params )->get
This method sets up a listening socket and arranges for an acceptor callback to be invoked
each time a new connection is accepted on the socket. Internally it creates an instance of
IO::Async::Listener and adds it to the Loop if not given one in the arguments.
Addresses may be given directly, or they may be looked up using the system's name
resolver, or a socket handle may be given directly.
If multiple addresses are given, or resolved from the service and hostname, then each will
be attempted in turn until one succeeds.
In named resolver mode, the %params hash takes the following keys:
service => STRING
The service name to listen on.
host => STRING
The hostname to listen on. Optional. Will listen on all addresses if not supplied.
family => INT
socktype => INT
protocol => INT
flags => INT
Optional. Other arguments to pass along with "host" and "service" to the
"getaddrinfo" call.
socktype => STRING
Optionally may instead be one of the values 'stream', 'dgram' or 'raw' to stand
for "SOCK_STREAM", "SOCK_DGRAM" or "SOCK_RAW". This utility is provided to allow
the caller to avoid a separate "use Socket" only for importing these constants.
It is necessary to pass the "socktype" hint to the resolver when resolving the
host/service names into an address, as some OS's "getaddrinfo" functions require this
hint. A warning is emitted if neither "socktype" nor "protocol" hint is defined when
performing a "getaddrinfo" lookup. To avoid this warning while still specifying no
particular "socktype" hint (perhaps to invoke some OS-specific behaviour), pass 0 as the
"socktype" value.
In plain address mode, the %params hash takes the following keys:
addrs => ARRAY
Reference to an array of (possibly-multiple) address structures to attempt to
listen on. Each should be in the layout described for "addr". Such a layout is
returned by the "getaddrinfo" named resolver.
addr => ARRAY
Shortcut for passing a single address to listen on; it may be passed directly with
this key, instead of in another array of its own. This should be in a format
recognised by IO::Async::OS's "extract_addrinfo" method. See also the "EXAMPLES"
section.
In direct socket handle mode, the following keys are taken:
handle => IO
The listening socket handle.
In either case, the following keys are also taken:
on_fail => CODE
Optional. A callback that is invoked if a syscall fails while attempting to create
a listening sockets. It is passed the name of the syscall that failed, the
arguments that were passed to it, and the error generated. I.e.
$on_fail->( "socket", $family, $socktype, $protocol, $! );
$on_fail->( "sockopt", $sock, $optname, $optval, $! );
$on_fail->( "bind", $sock, $address, $! );
$on_fail->( "listen", $sock, $queuesize, $! );
queuesize => INT
Optional. The queue size to pass to the listen(2) calls. If not supplied, then 3
will be given instead.
reuseaddr => BOOL
Optional. If true or not supplied then the "SO_REUSEADDR" socket option will be
set. To prevent this, pass a false value such as 0.
v6only => BOOL
Optional. If defined, sets or clears the "IPV6_V6ONLY" socket option on "PF_INET6"
sockets. This option disables the ability of "PF_INET6" socket to accept
connections from "AF_INET" addresses. Not all operating systems allow this option
to be disabled.
An alternative which gives more control over the listener, is to create the
IO::Async::Listener object directly and add it explicitly to the Loop.
This method accepts an "extensions" parameter; see the "EXTENSIONS" section below.
listen (void)
$loop->listen( %params )
When not returning a future, additional parameters can be given containing the
continuations to invoke on success or failure.
on_notifier => CODE
Optional. A callback that is invoked when the Listener object is ready to receive
connections. The callback is passed the Listener object itself.
$on_notifier->( $listener )
If this callback is required, it may instead be better to construct the Listener
object directly.
on_listen => CODE
Optional. A callback that is invoked when the listening socket is ready.
Typically this would be used in the name resolver case, in order to inspect the
socket's sockname address, or otherwise inspect the filehandle.
$on_listen->( $socket )
on_listen_error => CODE
A continuation this is invoked after all of the addresses have been tried, and
none of them succeeded. It will be passed the most significant error that
occurred, and the name of the operation it occurred in. Errors from the listen(2)
syscall are considered most significant, then bind(2), then sockopt(2), then
finally socket(2).
on_resolve_error => CODE
A continuation that is invoked when the name resolution attempt fails. This is
invoked in the same way as the "on_error" continuation for the "resolve" method.
OS ABSTRACTIONS
Because the Magic Constructor searches for OS-specific subclasses of the Loop, several
abstractions of OS services are provided, in case specific OSes need to give different
implementations on that OS.
signame2num
$signum = $loop->signame2num( $signame )
Legacy wrappers around IO::Async::OS functions.
time
$time = $loop->time
Returns the current UNIX time in fractional seconds. This is currently equivalent to
"Time::HiRes::time" but provided here as a utility for programs to obtain the time current
used by IO::Async for its own timing purposes.
fork
$pid = $loop->fork( %params )
This method creates a new child process to run a given code block, returning its process
ID.
code => CODE
A block of code to execute in the child process. It will be called in scalar
context inside an "eval" block. The return value will be used as the exit(2) code
from the child if it returns (or 255 if it returned "undef" or thows an
exception).
on_exit => CODE
A optional continuation to be called when the child processes exits. It will be
invoked in the following way:
$on_exit->( $pid, $exitcode )
The second argument is passed the plain perl $? value.
This key is optional; if not supplied, the calling code should install a handler
using the "watch_child" method.
keep_signals => BOOL
Optional boolean. If missing or false, any CODE references in the %SIG hash will
be removed and restored back to "DEFAULT" in the child process. If true, no
adjustment of the %SIG hash will be performed.
create_thread
$tid = $loop->create_thread( %params )
This method creates a new (non-detached) thread to run the given code block, returning its
thread ID.
code => CODE
A block of code to execute in the thread. It is called in the context given by the
"context" argument, and its return value will be available to the "on_joined"
callback. It is called inside an "eval" block; if it fails the exception will be
caught.
context => "scalar" | "list" | "void"
Optional. Gives the calling context that "code" is invoked in. Defaults to
"scalar" if not supplied.
on_joined => CODE
Callback to invoke when the thread function returns or throws an exception. If it
returned, this callback will be invoked with its result
$on_joined->( return => @result )
If it threw an exception the callback is invoked with the value of $@
$on_joined->( died => $! )
LOW-LEVEL METHODS
As "IO::Async::Loop" is an abstract base class, specific subclasses of it are required to
implement certain methods that form the base level of functionality. They are not
recommended for applications to use; see instead the various event objects or higher level
methods listed above.
These methods should be considered as part of the interface contract required to implement
a "IO::Async::Loop" subclass.
API_VERSION
IO::Async::Loop->API_VERSION
This method will be called by the magic constructor on the class before it is constructed,
to ensure that the specific implementation will support the required API. This method
should return the API version that the loop implementation supports. The magic constructor
will use that class, provided it declares a version at least as new as the version
documented here.
The current API version is 0.49.
This method may be implemented using "constant"; e.g
use constant API_VERSION => '0.49';
watch_io
$loop->watch_io( %params )
This method installs callback functions which will be invoked when the given IO handle
becomes read- or write-ready.
The %params hash takes the following keys:
handle => IO
The IO handle to watch.
on_read_ready => CODE
Optional. A CODE reference to call when the handle becomes read-ready.
on_write_ready => CODE
Optional. A CODE reference to call when the handle becomes write-ready.
There can only be one filehandle of any given fileno registered at any one time. For any
one filehandle, there can only be one read-readiness and/or one write-readiness callback
at any one time. Registering a new one will remove an existing one of that type. It is not
required that both are provided.
Applications should use a IO::Async::Handle or IO::Async::Stream instead of using this
method.
If the filehandle does not yet have the "O_NONBLOCK" flag set, it will be enabled by this
method. This will ensure that any subsequent "sysread", "syswrite", or similar will not
block on the filehandle.
unwatch_io
$loop->unwatch_io( %params )
This method removes a watch on an IO handle which was previously installed by "watch_io".
The %params hash takes the following keys:
handle => IO
The IO handle to remove the watch for.
on_read_ready => BOOL
If true, remove the watch for read-readiness.
on_write_ready => BOOL
If true, remove the watch for write-readiness.
Either or both callbacks may be removed at once. It is not an error to attempt to remove a
callback that is not present. If both callbacks were provided to the "watch_io" method and
only one is removed by this method, the other shall remain.
watch_signal
$loop->watch_signal( $signal, $code )
This method adds a new signal handler to watch the given signal.
$signal The name of the signal to watch to. This should be a bare name like "TERM".
$code A CODE reference to the handling callback.
There can only be one callback per signal name. Registering a new one will remove an
existing one.
Applications should use a IO::Async::Signal object, or call "attach_signal" instead of
using this method.
This and "unwatch_signal" are optional; a subclass may implement neither, or both. If it
implements neither then signal handling will be performed by the base class using a self-
connected pipe to interrupt the main IO blocking.
unwatch_signal
$loop->unwatch_signal( $signal )
This method removes the signal callback for the given signal.
$signal The name of the signal to watch to. This should be a bare name like "TERM".
watch_time
$id = $loop->watch_time( %args )
This method installs a callback which will be called at the specified time. The time may
either be specified as an absolute value (the "at" key), or as a delay from the time it is
installed (the "after" key).
The returned $id value can be used to identify the timer in case it needs to be cancelled
by the "unwatch_time" method. Note that this value may be an object reference, so if it is
stored, it should be released after it has been fired or cancelled, so the object itself
can be freed.
The %params hash takes the following keys:
at => NUM
The absolute system timestamp to run the event.
after => NUM
The delay after now at which to run the event, if "at" is not supplied. A zero or
negative delayed timer should be executed as soon as possible; the next time the
"loop_once" method is invoked.
now => NUM
The time to consider as now if calculating an absolute time based on "after";
defaults to "time()" if not specified.
code => CODE
CODE reference to the continuation to run at the allotted time.
Either one of "at" or "after" is required.
For more powerful timer functionality as a IO::Async::Notifier (so it can be used as a
child within another Notifier), see instead the IO::Async::Timer object and its
subclasses.
These *_time methods are optional; a subclass may implement neither or both of them. If it
implements neither, then the base class will manage a queue of timer events. This queue
should be handled by the "loop_once" method implemented by the subclass, using the
"_adjust_timeout" and "_manage_queues" methods.
This is the newer version of the API, replacing "enqueue_timer". It is unspecified how
this method pair interacts with the older "enqueue/requeue/cancel_timer" triplet.
unwatch_time
$loop->unwatch_time( $id )
Removes a timer callback previously created by "watch_time".
This is the newer version of the API, replacing "cancel_timer". It is unspecified how this
method pair interacts with the older "enqueue/requeue/cancel_timer" triplet.
enqueue_timer
$id = $loop->enqueue_timer( %params )
An older version of "watch_time". This method should not be used in new code but is
retained for legacy purposes. For simple watch/unwatch behaviour use instead the new
"watch_time" method; though note it has differently-named arguments. For requeueable
timers, consider using an IO::Async::Timer::Countdown or IO::Async::Timer::Absolute
instead.
cancel_timer
$loop->cancel_timer( $id )
An older version of "unwatch_time". This method should not be used in new code but is
retained for legacy purposes.
requeue_timer
$newid = $loop->requeue_timer( $id, %params )
Reschedule an existing timer, moving it to a new time. The old timer is removed and will
not be invoked.
The %params hash takes the same keys as "enqueue_timer", except for the "code" argument.
The requeue operation may be implemented as a cancel + enqueue, which may mean the ID
changes. Be sure to store the returned $newid value if it is required.
This method should not be used in new code but is retained for legacy purposes. For
requeueable, consider using an IO::Async::Timer::Countdown or IO::Async::Timer::Absolute
instead.
watch_idle
$id = $loop->watch_idle( %params )
This method installs a callback which will be called at some point in the near future.
The %params hash takes the following keys:
when => STRING
Specifies the time at which the callback will be invoked. See below.
code => CODE
CODE reference to the continuation to run at the allotted time.
The "when" parameter defines the time at which the callback will later be invoked. Must be
one of the following values:
later Callback is invoked after the current round of IO events have been processed by
the loop's underlying "loop_once" method.
If a new idle watch is installed from within a "later" callback, the installed one
will not be invoked during this round. It will be deferred for the next time
"loop_once" is called, after any IO events have been handled.
If there are pending idle handlers, then the "loop_once" method will use a zero timeout;
it will return immediately, having processed any IO events and idle handlers.
The returned $id value can be used to identify the idle handler in case it needs to be
removed, by calling the "unwatch_idle" method. Note this value may be a reference, so if
it is stored it should be released after the callback has been invoked or cancled, so the
referrant itself can be freed.
This and "unwatch_idle" are optional; a subclass may implement neither, or both. If it
implements neither then idle handling will be performed by the base class, using the
"_adjust_timeout" and "_manage_queues" methods.
unwatch_idle
$loop->unwatch_idle( $id )
Cancels a previously-installed idle handler.
watch_child
$loop->watch_child( $pid, $code )
This method adds a new handler for the termination of the given child process PID, or all
child processes.
$pid The PID to watch. Will report on all child processes if this is 0.
$code A CODE reference to the exit handler. It will be invoked as
$code->( $pid, $? )
The second argument is passed the plain perl $? value.
After invocation, the handler for a PID-specific watch is automatically removed. The all-
child watch will remain until it is removed by "unwatch_child".
This and "unwatch_child" are optional; a subclass may implement neither, or both. If it
implements neither then child watching will be performed by using "watch_signal" to
install a "SIGCHLD" handler, which will use "waitpid" to look for exited child processes.
If both a PID-specific and an all-process watch are installed, there is no ordering
guarantee as to which will be called first.
unwatch_child
$loop->unwatch_child( $pid )
This method removes a watch on an existing child process PID.
METHODS FOR SUBCLASSES
The following methods are provided to access internal features which are required by
specific subclasses to implement the loop functionality. The use cases of each will be
documented in the above section.
_adjust_timeout
$loop->_adjust_timeout( \$timeout )
Shortens the timeout value passed in the scalar reference if it is longer in seconds than
the time until the next queued event on the timer queue. If there are pending idle
handlers, the timeout is reduced to zero.
_manage_queues
$loop->_manage_queues
Checks the timer queue for callbacks that should have been invoked by now, and runs them
all, removing them from the queue. It also invokes all of the pending idle handlers. Any
new idle handlers installed by these are not invoked yet; they will wait for the next time
this method is called.
EXTENSIONS
An Extension is a Perl module that provides extra methods in the "IO::Async::Loop" or
other packages. They are intended to provide extra functionality that easily integrates
with the rest of the code.
Certain base methods take an "extensions" parameter; an ARRAY reference containing a list
of extension names. If such a list is passed to a method, it will immediately call a
method whose name is that of the base method, prefixed by the first extension name in the
list, separated by "_". If the "extensions" list contains more extension names, it will be
passed the remaining ones in another "extensions" parameter.
For example,
$loop->connect(
extensions => [qw( FOO BAR )],
%args
)
will become
$loop->FOO_connect(
extensions => [qw( BAR )],
%args
)
This is provided so that extension modules, such as IO::Async::SSL can easily be invoked
indirectly, by passing extra arguments to "connect" methods or similar, without needing
every module to be aware of the "SSL" extension. This functionality is generic and not
limited to "SSL"; other extensions may also use it.
The following methods take an "extensions" parameter:
$loop->connect
$loop->listen
If an extension "listen" method is invoked, it will be passed a "listener" parameter even
if one was not provided to the original "$loop->listen" call, and it will not receive any
of the "on_*" event callbacks. It should use the "acceptor" parameter on the "listener"
object.
STALL WATCHDOG
A well-behaved IO::Async program should spend almost all of its time blocked on input
using the underlying "IO::Async::Loop" instance. The stall watchdog is an optional
debugging feature to help detect CPU spinlocks and other bugs, where control is not
returned to the loop every so often.
If the watchdog is enabled and an event handler consumes more than a given amount of real
time before returning to the event loop, it will be interrupted by printing a stack trace
and terminating the program. The watchdog is only in effect while the loop itself is not
blocking; it won't fail simply because the loop instance is waiting for input or timers.
It is implemented using "SIGALRM", so if enabled, this signal will no longer be available
to user code. (Though in any case, most uses of "alarm()" and "SIGALRM" are better served
by one of the IO::Async::Timer subclasses).
The following environment variables control its behaviour.
IO_ASYNC_WATCHDOG => BOOL
Enables the stall watchdog if set to a non-zero value.
IO_ASYNC_WATCHDOG_INTERVAL => INT
Watchdog interval, in seconds, to pass to the alarm(2) call. Defaults to 10 seconds.
IO_ASYNC_WATCHDOG_SIGABRT => BOOL
If enabled, the watchdog signal handler will raise a "SIGABRT", which usually has the
effect of breaking out of a running program in debuggers such as gdb. If not set then
the process is terminated by throwing an exception with "die".
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>