var GlobalCallQueue = {
    _callQueue : [],    // Maintains the list of webmethods to call
    _callInProgress : 0,    // Number of calls currently in progress by browser
    _maxConcurrentCall : 2, // Max number of calls to execute at a time
    _delayBetweenCalls : 50, // Delay between execution of calls 
    call : function(servicePath, methodName, useGet, 
        params, onSuccess, onFailure, userContext, timeout)
    {
        var queuedCall = new QueuedCall(servicePath, methodName, useGet, 
            params, onSuccess, onFailure, userContext, timeout);

        Array.add(GlobalCallQueue._callQueue,queuedCall);
        GlobalCallQueue.run();
    },
    run : function()
    {
        /// Execute a call from the call queue
        
        if( 0 == GlobalCallQueue._callQueue.length ) return;
        if( GlobalCallQueue._callInProgress < 
            GlobalCallQueue._maxConcurrentCall )
        {
            GlobalCallQueue._callInProgress ++;
            // Get the first call queued
            var queuedCall = GlobalCallQueue._callQueue[0];
            Array.removeAt( GlobalCallQueue._callQueue, 0 );
            
            // Call the web method
            queuedCall.execute();
        }
        else
        {
            // cannot run another call. Maximum concurrent 
            // webservice method call in progress
        }            
    },
    callComplete : function()
    {
        GlobalCallQueue._callInProgress --;
        GlobalCallQueue.run();
    }
};

QueuedCall = function( servicePath, methodName, useGet, params, 
    onSuccess, onFailure, userContext, timeout )
{
    this._servicePath = servicePath;
    this._methodName = methodName;
    this._useGet = useGet;
    this._params = params;
    
    this._onSuccess = onSuccess;
    this._onFailure = onFailure;
    this._userContext = userContext;
    this._timeout = timeout;
}

QueuedCall.prototype = 
{
    execute : function()
    {
        Sys.Net.WebServiceProxy.original_invoke( 
            this._servicePath, this._methodName, this._useGet, this._params,  
            Function.createDelegate(this, this.onSuccess), // Handle call complete
            Function.createDelegate(this, this.onFailure), // Handle call complete
            this._userContext, this._timeout );
    },
    onSuccess : function(result, userContext, methodName)
    {
        this._onSuccess(result, userContext, methodName);
        GlobalCallQueue.callComplete();            
    },        
    onFailure : function(result, userContext, methodName)
    {
        this._onFailure(result, userContext, methodName);
        GlobalCallQueue.callComplete();            
    }        
};

//=====================================

Sys.Net.WebServiceProxy.original_invoke = Sys.Net.WebServiceProxy.invoke;
Sys.Net.WebServiceProxy.invoke = 
    function Sys$Net$WebServiceProxy$invoke(servicePath, methodName, 
        useGet, params, onSuccess, onFailure, userContext, timeout)
{   
    GlobalCallQueue.call(servicePath, methodName, useGet, params, 
        onSuccess, onFailure, userContext, timeout);
}