Also, I still recommend using AsyncSocket instead of NSStream APIs as
AsyncSocket will make your life much simpler at pretty much no cost.
-Steven
On Wed, Jan 20, 2010 at 11:39 AM, Carter R. Harrison <carterharri...@mac.com
> wrote:
> I need some folks experienced with cocoa and socket programming to weigh in
> for me on some design problems I've been having. I'm designing an
> application that acts as a client in a client-server model. The client
> communicates with the server over the network by issuing a request and then
> receiving a response. Requests can only be issued one at a time, meaning
> that a request cannot be sent until a response from any outstanding request
> is first received. My application works in such a way that the it could
> request a handle to an object on the server and then use that handle in
> subsequent requests to retrieve additional information about the object. I
> see two ways of modeling the application - I've tried both and I'm not
> particularly happy with either.
>
> The first is to send a request, and then have the socket block until a
> response is received. This benefit to this model is that it is so much
> easier to write the higher level application code. The issue with this
> model is that over a slow network connection it can take a considerable
> amount of time for the response to come back from the server and while that
> is happening my CPU usage is through the roof b/c the thread is blocking.
>
> The second way is to send a request and then let the NSInputStream call a
> delegate method when the response data is available. The response data is
> then pushed up through my protocol stack and finally up to the higher level
> application code. The benefit to this method is that CPU usage is minimal
> due to the fact that I'm no longer blocking, but the downside is that the
> higher level application code is so much more difficult to write because I
> have to write about a thousand methods to act as a callback for each request
> in a series of requests.
>
> I've provided an example of how I see each working below. My first
> question is, is there other ways to design an application around this
> client-server model that I'm not thinking about? My 2nd question is, if
> there aren't other ways, how can I adapt either method that I have outlined
> to make it work a little bit better?
>
> As an example let's say the server knows about the following objects:
>
> 1. VendingMachine
> - An object that represents a vending machine.
> - A vending machine contains Soft Drink objects.
> 2. SoftDrink
> - Has the following properties: drink name, price, number of
> calories.
>
> If I use the blocking model, I could write my code like this. The code is
> simple to write but I'm forced to wait for the server to respond with
> information on pretty much every line of code. If the vending machine had
> enough soft drinks it could take a long time to iterate over each one and
> have the server respond with the drink's name of each drink.
>
> -(void)printDrinkNames
> {
> VendingMachine *machine = [server fetchVendingMachine];
> NSArray *softDrinks = [machine getSoftDrinks];
> for (int i = 0 ; i < softDrinks.count ; i++)
> {
> NSString *drinkName = [[softDrinks objectAtIndex:i] name];
> NSLog(@"Found a drink named %@", drinkName);
> }
> }
>
> Likewise if I do the non-blocking approach I would have to have a method
> that gets called for each step in the process (see below). This model
> drives me crazy b/c the higher level application code is long, has tons of
> methods, and is just difficult to read and maintain. The example I have
> provided is simple enough to get the point across, but in reality some of
> the processes I'm trying to drive are much more complex and require numerous
> callback methods to pull off.
>
> -(void)printDrinkNames
> {
> [server fetchVendingMachineWithCallBackObject:self
> selector:@selector(didFetchVendingMachine:)
> }
>
> -(void)didFetchVendingMachine:(VendingMachine *)machine
> {
> [machine fetchSoftDrinksWithCallBackObject:self selector:@selector
> (didFetchSoftDrinks:)];
> }
>
> -(void)didFetchSoftDrinks:(NSArray *)drinks
> {
> for (int i = 0 ; i < drinks.count ; i++)
> {
> SoftDrink *drink = [drinks objectAtIndex:i];
> [drink fetchNameWithCallBackObject:self selector:@selector
> (didFetchDrinkName:)]
> }
> }
>
> -(void)didFetchDrinkName:(NSString *)name
> {
> NSLog(@"Drink name is %@", name);
> }
>
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--
Steven Degutis
http://www.thoughtfultree.com/
http://www.degutis.org/
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