MACROMEDIA FLASH COMMUNICATION SERVER MX-SERVER-SIDE COMMUNICATION ACTIONSCRIPT DICTIONARY Spécifications télécharger pdf (Page 160)

Chapter 482

Assign an owner

A more complex strategy is to define a single client as the owner of a property

in a shared object for a limited period of time. You might write server code to create a “lock”

object, where a client can request ownership of a slot. If the server reports that the request was

successful, the client knows that it will be the only client changing the data in the shared object.

Here’s some server-side ActionScript that locks and unlocks a shared object to make sure the true

highest score is returned to the game. Suppose the most recent highest score was 95, and player 1’s

score increased to 105, while player 2’s score increased to 110. If no locking occurred, both

players’ scores could be compared to the most recent highest score, 95, or a collision could take

place if both clients call

updateHighScore simultaneously. You’d want to make sure that each

player was compared to the highest score, regardless of whether it was the most recent highest

score or any score currently coming in from all other clients. If you lock and unlock the shared

object used to store the highest score, you can compare each score sequentially, and thus ensure

that no comparison is lost.

application.onAppStart = function()

{

application.scoreSO = SharedObject.get("high_score_so", true);

application.scoreSO.onSync = function(listVal)

{

trace("got an onSync on scoreSO");

}

application.onConnect = function(newClient,name,passwd)

{

newClient.updateHighScore = function(final_score)

{

application.scoreSO.lock();

if (application.scoreSO.getProperty("high_score_so") < final_score)

{

application.scoreSO.setProperty("high_score_so", final_score);

}

application.scoreSO.unlock();

}

Notify the client When the server rejects a client-requested change to a property of the shared

object, the SharedObject.onSync event handler notifies the client that the change was rejected.

Thus, an application can provide a user interface to let a user resolve the conflict. This technique

works best if data is changed infrequently, as in a shared address book. If a synchronization

conflict occurs, the user can decide whether to accept or reject the change.

Accept some changes and reject others Some applications can accept changes on a “first come,

first served” basis. This works best when users can resolve conflicts by reapplying a change if

someone else’s change preceded theirs.

Use the send method to increase your level of control over changes to objects Rather than

relying completely on

SharedObject.onSync to manage synchronization activities, use the

SharedObject.send command as appropriate. The SharedObject.send command broadcasts

a message to all clients connected to a remote shared object, including the client that sent the

message.

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