How do I delay tasks , so never more than one a second?
Im using Java 1.5 I currently have a single thread that as aprt of its processing sends urls to a website, the terms of service of the website state that there must be a 1 second delay between each request. I dont want to break that condition but I want to keep the application as fast as possible.
What's the simplest way to achieve this, I looked at DelayQueue and thought of adding another thread that took items of the queue and processed them but I couldnt see how this could work because the delay if any between processing the urls is
1 SECOND - (TIME LAST URL SENT - TIME URL RECIEVED ) so I cant work out an absolute delay when I add to the queue, and besides I would prefer to keep single threaded if possible.
this is an urgent problem, thanks for any help
Ok, thanks very much that works.
I have a followup question, actually my code was originally multithreaded but I changed to single threaded to try and meet the terms of service of the webserver. Now i want to revert back to multithreaded keeping the delay code added because sometimes the responses are taking a few seconds, so if it was multithreaded another thread could send another requested one second after the first thread whilst that thread was waiting for a response to speed up throughput.
But I dont think the solution will work in this case even though the method is sychronized because as soon as one Thread sleeps, another thread can interrupt it and send a response itself before the thread has finished sleeping (i.e before the second is up) How can I solve this, code exerpt below:
thanks paul
private static volatile DatequerySentDate = new Date();
private static SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss:SSS");
private static long DELAY_IN_MILLISECONDS = 1000;
public static synchronized Metadata performQuery() throws NetworkException, InvalidQueryException
{
Date currentDate = new Date();
long delay = currentDate.getTime() - querySentDate.getTime();
if( delay < DELAY_IN_MILLISECONDS)
{
try
{
Thread.sleep(DELAY_IN_MILLISECONDS - (delay ));
}
catch(InterruptedException ie)
{
return null;
}
}
querySentDate = new Date();
Metadata metadata = null;
URL url = null;
BufferedInputStream bis = null;
HttpURLConnection uc = null;
try
{
url = new URL(getBaseQueryUrl() + sb.toString());
uc = (HttpURLConnection) url.openConnection();
int responseCode = uc.getResponseCode();
if (responseCode != HttpURLConnection.HTTP_OK)
{
throw new InvalidQueryException();
}
bis = new BufferedInputStream(uc.getInputStream());
JAXBContext jc = JAXBContext.newInstance("com.test.dataformat");
Unmarshaller um = jc.createUnmarshaller();
metadata = (Metadata) um.unmarshal(bis);
}
catch (IOException e)
{
throw new NetworkException("Unable to connect");
}
return metadata;
}
