Databases
StackOverflow2013
Postsdbo
POTo use multithreading, is Command pattern more useful than Decorator pattern?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POTo use multithreading, is Command pattern more useful than Decorator pattern?
    primarykey
    data
    text
    <p>Having seen how <a href="http://en.wikipedia.org/wiki/Command_pattern" rel="nofollow">Command pattern</a> was used in a previous project, I can understand how it can be useful in multithreaded (parallel) programming, because Commands can be executed in different threads. When data needs to be passed between commands, the data can be stored in a shared memory and a pointer (or handle) to that data can be passed to an invoker on a differeht thread.</p> <p>However, Decorator pattern seems to have the restriction that everything must happen on a single thread, because the decorator has to call the delegate directly, implying they must be on the same thread.</p> <p>Is my understanding of this limitation correct? On the contrary, is it possible to run decorator on multiple threads?</p> <hr> <p>What I'm trying to implement is a pipeline that processes a stream of data.</p> <ul> <li>To implement as Command pattern, its <code>execute</code> method would take two arguments: a buffer for input and a buffer for output.</li> <li>To implement as Decorator pattern, its <code>getdata</code> method would call its delegate to get the result of the previous step, apply its own processing, and return the result to the caller.</li> </ul> <p>However after I have implemented it in both styles, I found that each has limitations that wasn't clear to me originally.</p> <ul> <li>When using the Command pattern, I can start accepting more input data by using a new buffer, while the earlier buffers are being processed by some Commands running in separate work threads. I can't seem to do this with Decorator pattern.</li> <li>When using the Decorator pattern, the decorator can make any number of calls to its delegate and be able to combine the results into one chunk. It can also split data, by making one big request, cache it, and then returning pieces of it. When I use Command pattern with one input buffer and one output buffer, there cannot be any combination or splitting of results.</li> </ul>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USrwong
    1. USrwong
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POTo use multithreading, is Command pattern more useful than Decorator pattern?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COhuh. I fail to see the connection between decorator and threading. These are orthogonal concepts in my view. How does one 'call' or 'execute' a decorator? Decorators are a way to [`add behaviour to an existing object dynamically`](http://en.wikipedia.org/wiki/Decorator_pattern)
      singulars
      1. POTo use multithreading, is Command pattern more useful than Decorator pattern?
      1. USsehe
    2. CODecorators can be used to make any class thread safe, by wrapping objects into synchronized methods. In any case usefulness of a pattern is topic too subjective to get an answer here.
      singulars
      1. POTo use multithreading, is Command pattern more useful than Decorator pattern?
      1. USilcavero
    3. CO@sehe: there are some frameworks where the bulk of processing is carried out by decorators, by performing additional processing on the data returned from its delegate. I know that decorators (as described originally) are supposed to be lightweight (they provide a good syntax for the users), so maybe the heavyweight decorator shouldn't be caller a decorator?
      singulars
      1. POTo use multithreading, is Command pattern more useful than Decorator pattern?
      1. USrwong
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload