How can I generate a piped NSData

Question

I was intercepting AJAX request in cachedResponseForRequest:, and then construct a custom Response for the request. But it seems that this API method always work on a same thread, so if I was doing a time consuming operation, new requests would be blocked. In Android, I solved this problem using PipedStream, But cachedResponseForRequest: returns response with NSData, How can I make NSData pipable, can anybody help me out

Here is My Code:

- (NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request
{
    NSURL *url=request.URL;
    NSCachedURLResponse *response=nil;
    if([url.path containsString:@"aa1"]){
        NSMutableData *data=[NSMutableData data];
        NSThread* asyncThread = [[NSThread alloc] initWithTarget:self selector:@selector(getData:) object:data];
        [asyncThread start];
        NSURLResponse *urlresponse=[[NSURLResponse alloc] initWithURL:url MIMEType:@"application/json" expectedContentLength:data.length textEncodingName:@"utf-8"];
        response=[[NSCachedURLResponse alloc] initWithResponse:urlresponse data:data];

    }
    return response;
}

-(void)getData:(NSMutableData*)data{
    NSMutableString *str=[NSMutableString stringWithString:@""];
    for(int i=0;i<1024*1024;i++){
        [str appendFormat:@"s"];
    }
    [data appendData:[str dataUsingEncoding:NSUTF8StringEncoding]];
    NSLog(@"%d",data.length);
}

And In android, I solved this matter like follow

public WebResourceResponse shouldInterceptRequest(WebView view,
            String url) {
    WebResourceResponse response = null;
    if (url.contains("loca/aa0")) {
        try {
            final PipedOutputStream out = new PipedOutputStream();
            InputStream in = new PipedInputStream(out);
            AsyncTask<String, Integer, String> task = new AsyncTask<String, Integer, String>() {
                @Override
                protected String doInBackground(String... params) {
                    // TODO Auto-generated method stub
                    try {
                        InputStream s = ctx.getAssets().open("s.txt");
                        byte[] buffer = new byte[100];
                        while (s.read(buffer) != -1)
                            out.write(buffer);
                        out.flush();
                        out.close();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return null;
                }
            };
            task.execute();
            response = new WebResourceResponse("application/html","UTF-8", in);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    return response;
}

can anybody see my Question?