Module: Concurrent::Concern::Observable
- Defined in:
- lib/concurrent-ruby/concurrent/concern/observable.rb
Overview
The observer pattern is one of the most useful design patterns.
The workflow is very simple:
- an
observer
can register itself to asubject
via a callback - many
observers
can be registered to the samesubject
- the
subject
notifies all registered observers when its status changes - an
observer
can deregister itself when is no more interested to receive event notifications
In a single threaded environment the whole pattern is very easy: the
subject
can use a simple data structure to manage all its subscribed
observer
s and every observer
can react directly to every event without
caring about synchronization.
In a multi threaded environment things are more complex. The subject
must
synchronize the access to its data structure and to do so currently we're
using two specialized ObserverSet: CopyOnWriteObserverSet
and CopyOnNotifyObserverSet.
When implementing and observer
there's a very important rule to remember:
there are no guarantees about the thread that will execute the callback
Let's take this example
class Observer
def initialize
@count = 0
end
def update
@count += 1
end
end
obs = Observer.new
[obj1, obj2, obj3, obj4].each { |o| o.add_observer(obs) }
# execute [obj1, obj2, obj3, obj4]
obs
is wrong because the variable @count
can be accessed by different
threads at the same time, so it should be synchronized (using either a Mutex
or an AtomicFixum)
Instance Method Summary collapse
-
#add_observer(observer = nil, func = :update, &block) ⇒ Object
Adds an observer to this set.
-
#count_observers ⇒ Integer
Return the number of observers associated with this object.
-
#delete_observer(observer) ⇒ Object
Remove
observer
as an observer on this object so that it will no longer receive notifications. -
#delete_observers ⇒ Observable
Remove all observers associated with this object.
-
#with_observer(observer = nil, func = :update, &block) ⇒ Observable
As
#add_observer
but can be used for chaining.
Instance Method Details
#add_observer(observer = nil, func = :update, &block) ⇒ Object
Adds an observer to this set. If a block is passed, the observer will be created by this method and no other params should be passed.
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# File 'lib/concurrent-ruby/concurrent/concern/observable.rb', line 61 def add_observer(observer = nil, func = :update, &block) observers.add_observer(observer, func, &block) end |
#count_observers ⇒ Integer
Return the number of observers associated with this object.
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# File 'lib/concurrent-ruby/concurrent/concern/observable.rb', line 101 def count_observers observers.count_observers end |
#delete_observer(observer) ⇒ Object
Remove observer
as an observer on this object so that it will no
longer receive notifications.
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# File 'lib/concurrent-ruby/concurrent/concern/observable.rb', line 82 def delete_observer(observer) observers.delete_observer(observer) end |
#delete_observers ⇒ Observable
Remove all observers associated with this object.
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# File 'lib/concurrent-ruby/concurrent/concern/observable.rb', line 91 def delete_observers observers.delete_observers self end |
#with_observer(observer = nil, func = :update, &block) ⇒ Observable
As #add_observer
but can be used for chaining.
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# File 'lib/concurrent-ruby/concurrent/concern/observable.rb', line 70 def with_observer(observer = nil, func = :update, &block) add_observer(observer, func, &block) self end |