Event::var

📦 max

A var watcher: an event whenever a scalar variable is written to, or read. Its events are Event::Event::Io objects, whose got is w for a write and r for a read.

Event->var(%attributes) (or Event::var->new(...)) takes the shared attributes of Event::Watcher and the ones below. A var watcher repeats; its default priority is PRIO_NORMAL. It refuses to start without a callback, without a variable (“watching what?”), with an empty poll, or on a read-only variable.

Perl reads variables in more places than are apparent from the source, so watching reads is rarely what is wanted; the default is to watch writes only.

Synopsis

use Event;

my $status = 'idle';
Event->var(var => \$status, cb => sub { print "status: $status\n" });
Event->timer(after => 1, cb => sub { $status = 'busy' }, repeat => 0);
Event::loop(2);

Functions

Attributes

var

The variable, as a reference to a plain scalar. A reference to an array, hash or anything else beyond a scalar dies “Var watchers can only watch plain vanilla scalars”, and a value that is no reference dies “Expecting a reference”. The watcher keeps the reference it was given.

poll

What to watch for: "w" (writes, the default), "r" (reads) or "rw", or the number made of the bits R and W (see Event::Watcher). The value returned is both the string and the number.