Object lifecycle and Loop attachment

Linux::Event has one owner of readiness: Linux::Event::Loop. It does not require a public Watcher base class. Public objects implement their own lifecycle and expose a private _attach_to_loop hook that Loop->add() uses. The hook is an implementation contract between this distribution's classes, not an application subclass API.

Two equivalent construction styles

Every attachable public class accepts loop => $loop:

my $stream = ClientStream->connect(
    loop => $loop, host => '127.0.0.1', port => 9999,
);

my $listener = Linux::Event::Listener->new(
    loop => $loop, stream_class => 'ServerStream',
    host => '0.0.0.0', port => 9999,
);

my $timer = SessionTimer->new(
    loop => $loop, after => 30, data => $session,
);

my $signal = ShutdownSignal->new(
    loop => $loop, signals => [SIGINT, SIGTERM], data => $server,
);

my $datagram = MetricsDatagram->new(
    loop => $loop, host => '0.0.0.0', port => 9000,
);

my $wakeup = ResultWakeup->new(
    loop => $loop, data => $result_queue,
);

my $process = WorkerProcess->spawn(
    loop => $loop, command => ['/usr/bin/worker', '--once'],
);

An object may instead be constructed detached and passed to add():

my $stream = $loop->add(ClientStream->connect(
    host => '127.0.0.1', port => 9999,
));

my $listener = $loop->add(Linux::Event::Listener->new(
    stream_class => 'ServerStream',
    host => '0.0.0.0', port => 9999,
));

my $timer = $loop->add(SessionTimer->new(
    after => 30, data => $session,
));

my $signal = $loop->add(ShutdownSignal->new(
    signals => [SIGINT, SIGTERM], data => $server,
));

my $datagram = $loop->add(MetricsDatagram->new(
    host => '0.0.0.0', port => 9000,
));

my $wakeup = $loop->add(ResultWakeup->new(
    data => $result_queue,
));

my $process = $loop->add(WorkerProcess->spawn(
    command => ['/usr/bin/worker', '--once'],
));

add() sets the object's Loop, starts its activity, and returns the same object. Neither style is a compatibility adapter; they are equal parts of the public API. The constructor form is concise when the Loop is already known. The detached form is useful when configuration and activation happen in different parts of an application.

Ownership rules

• An attachable object belongs to at most one Loop.
• An object can be attached only once.
• A terminal object cannot be reattached.
• Stream owns its established socket from construction or successful connect until close(), detach(), or destruction.
• A deadline-enabled Stream owns at most one private Timer in its Loop's shared scheduler. Close, detach, failure, and Loop destruction cancel that entry.
• Listener owns sockets it creates. An adopted listener is closed only when owns_socket => 1 was requested.
• Loop retains an active Timer even when the application drops its reference. A one-shot Timer releases its data after callback completion; recurring Timers retain it until cancellation or Loop destruction.
• Loop retains active Signal objects through one shared native signalfd service. Cancellation or Loop destruction restores Loop-owned mask entries and releases retained data.
• Datagram owns created sockets and Unix paths. Adopted handles default to caller ownership. detach() returns an open handle and disables path removal.
• Wakeup owns one eventfd and its Loop registration. Only signal() may be used from a cloned ithread handle or forked child.
• Loop retains a running Process. Process owns its pidfd and pipe ends but does not implicitly signal a child on destruction.
• add() returns the exact object it received; it does not wrap or replace it.

Violations are rejected synchronously. This makes the Loop registry and native descriptor ownership unambiguous.

Logical objects and native registrations

A public object is a logical activity, not a one-to-one wrapper around an epoll entry. A connecting Stream can temporarily own a socket registration and a timerfd registration. After connection it owns the established socket registration. The application continues to hold one Stream object throughout.

Listener similarly owns its listening registration and creates Stream objects for accepted sockets. It attaches each Stream before the optional Listener on_accept callback; plain Stream on_ready follows that callback, while TLS Stream on_ready follows its successful handshake. Listener passes its data value to each accepted Stream. These native registrations are implementation details.

Timer is also a logical object rather than a timerfd wrapper. All active Timers on one Loop share one lazily created timerfd and live in a native indexed heap. Cancellation is terminal and idempotent. Rescheduling is allowed while active or from inside on_timer, but an expired or cancelled Timer cannot be revived. Private Stream deadline Timers follow the same scheduler rules but are not application objects. Their data holds only a weak route to the owning Stream, so deadline ownership does not introduce a Perl reference cycle.

Signal is a logical subscription rather than a signalfd wrapper. All Signal objects on one Loop share one signalfd and native fan-out registry. One object may subscribe to several numbers and several objects may subscribe to the same number on that Loop.

Wakeup is a logical notification rather than an eventfd registration handle. Its eventfd counter says that external work may be available; the associated thread-safe queue or IPC channel remains the source of payloads.

Datagram owns a packet socket and whole-packet output queue. Process may own a pidfd plus four registrations: pidfd, stdin, stdout, and stderr. These remain one application object because their lifecycle and callbacks are inseparable.

Raw descriptor registrations

Low-level applications can register a descriptor directly:

my $registration = $loop->watch(
    fh   => $fh,
    read => sub ($registration) {
        my $count = sysread($registration->fh, my $bytes, 8192);
        $registration->cancel if defined($count) && $count == 0;
    },
);

watch() attaches immediately and returns an opaque native registration handle. It supports readiness-interest changes, accessors, and cancel(), but it is not a public class hierarchy and must not be subclassed. Use Stream or Listener when the resource needs a higher-level ownership policy.

Destruction

Explicit close() is recommended because it makes application intent and callback timing clear. Destructors are a safety net. Stream fires on_close once when it closes an owned connection, but detach() deliberately does not: the resource remains open and ownership transfers to the caller.

For Timer, explicit cancel() is the corresponding terminal operation. Loop destruction cancels every remaining Timer and releases its retained data. If a Timer cancels itself during on_timer, cleanup is deferred until the callback returns so callback-local access remains safe.

Signal cancellation follows the same terminal rule. Self-cancellation and cross-cancellation during fan-out are safe; callback-local data remains visible until the active callback returns.

Datagram close() releases an owned socket and path and calls on_close; detach() transfers the handle without calling on_close. Process has no generic cancellation method: applications close stdin or send an explicit signal and retain the Loop until on_exit.

Interpreter ownership

Loop and every native resource-owning object are confined to their creating Perl interpreter and opt out of ithread cloning. Wakeup is the single narrow exception: the clone contains only enough scalar state to write the shared eventfd through its own descriptor duplicate. It does not clone the Loop graph, callbacks, registrations, or owner data. This prevents double-close and native-pointer reuse across interpreters.

Class declarations remain available in a child ithread. Stream, Timer, and Signal rebuild their immutable native class descriptors there on first use, so the child may create its own independent resources and Loop. An object created before the thread boundary still belongs only to its original interpreter.