Module: Concurrent::Concern::Observable
- Defined in:
- lib/concurrent-ruby/concurrent/concern/observable.rb
Overview
The [observer pattern](en.wikipedia.org/wiki/Observer_pattern) is one of the most useful design patterns.
The workflow is very simple:
-
an ‘observer` can register itself to a `subject` via a callback
-
many ‘observers` can be registered to the same `subject`
-
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 |