aSyncSelectStatementCallback

aSyncSelectStatementCallback.js

/*
First draft at making an asynchronous method for returning a large SELECT result from SQLite in Firefox.

As part of a discussion here:
https://bugzilla.mozilla.org/show_bug.cgi?id=608142

Aiming to be an expansion of:
https://developer.mozilla.org/en/storage#Asynchronously
*/


function aSyncSelectStatementCallback()
{
    this.rowsPerInterval = 1; // may want to experiment with for speed
    this.timePerInterval = 1; // may want to experiment with for speed
    this.intervals = [];
}
aSyncSelectStatementCallback.prototype =
{            
    // errors
    handleError : function(aError) { Components.utils.reportError(aError.message); },
    
    // Only use this to listen to cancel/error messages.
    // REASON_FINISHED is sent when all intervals have started, not when they are actually done, use handleFinished for that
    handleCompletion : function(aReason) 
    { 
        if (aReason == 0 && this.intervals.length==0)
            this.handleFinished();
    },
    
    // When all rows have been processed and all intervals are finished
    handleFinished : function() {  },
    
    // Processes each row on against the event loop
    handleResult : function(aResultSet)
    {
        var c = this.intervals.length;
        this.intervals[c] = true;
        var interval = this.setInterval(function()
        {                
            let row;
            
            for(let i=0; i<this.rowsPerInterval; i++)
            {
                row = aResultSet.getNextRow();
            
                if (row)
                    this.handleRow(row);
                
                else
                {
                    this.clearTimeout(interval);
                    this.intervals[c] = false;
                    
                    // check if all intervals have completed
                    // start at end, assuming they get completed from first to last
                    for(let i=this.intervals.length-1; i>=0; i--)
                    {
                        if (this.intervals[i])
                            return;
                    }
                    
                    // all intervals are completed
                    this.handleFinished();
                    return;
                }
            }
            
        }, this.timePerInterval, this);
    },
    
    // interval methods

    setInterval : function(func, time)
    {
        let callback = {obj:this, notify:function(){func.call(this.obj)}};                
        let timer = Components.classes["@mozilla.org/timer;1"].createInstance(Components.interfaces.nsITimer);
        timer.initWithCallback(callback, time, Components.interfaces.nsITimer.TYPE_REPEATING_SLACK);
        return timer;
    },
    
    clearTimeout : function(timer)
    {
        if (timer)
            timer.cancel();
        return timer;
    }
}

// example function to call when all of the results have been fetched
function hereAreYourNames(names)
{
    alert( names );
}

// Create the callback and define the methods for handling each row
var callback = new aSyncSelectStatementCallback();
callback.names = [];
callback.handleRow = function(aRow) {
    this.names.push( aRow.getResultByName("first_name") );
}
callback.handleFinished = function() {
    hereAreYourNames(this.names);
}

// Execute the SQLite statement
statement.executeAsync(callback);