用几个请求终止Java中的线程？

Question

Suppose I have a method in a CLIENT Java application (ie Android app)

ExecutorService pool = ExecutorsService.newFixedThreadPool(1); //1 thread in pool

public void makeHTTPRequestVeryVeryCostly() { 
  /* IN A BACKGROUND THREAD */
   CompleteableFuture<String> s = CompleteableFuture.supplyAsync(() -> makeCostlyReq, pool));  
   s.get();
   updateTheUserUIInTheMainUIThread(s); //Update with s
}

button.onClicklistener((b) -> makeHTTPRequestVeryVeryCostly()); // some button in the UI that will make the http request

In anger, the user taps the button 100 times, then 100 requests have been submitted into the ThreadPool. 2 bad things occur:

(1) Costly request computed 100 times

(2) The UI is refreshed 100 times after each return.

These are all very big issues. In Java, what's the way of solving this? It would be best to terminate all preceeding requests in the thread pool after one sucessful request, how can this be done?

Answer 1

If you want send each http request, but no concurrency。 Lock may help you here. Below pseudo-code:

ExecutorService pool = ExecutorsService.newFixedThreadPool(1); //1 thread in pool
Lock httpRequestLock = new ReentrantLock();

public void makeHTTPRequestVeryVeryCostly() {
   boolean locked = httpRequestLock.tryLock(10, TimeUnit.SECONDS);
   if(!locked){
     //can't get the request lock util timeout(10s)
     return;
   }

   try{
      /* IN A BACKGROUND THREAD */
       CompleteableFuture<String> s = CompleteableFuture.supplyAsync(() -> makeCostlyReq, pool));  
       s.get();
       updateTheUserUIInTheMainUIThread(s); //Update with s
   }finally{
       httpRequestLock.unlock();
   }
}

button.onClicklistener((b) -> makeHTTPRequestVeryVeryCostly()); // some button in the UI that will make the http request

We use a Lock to ensure only one request at same time, and set a timeout to follow-up request when get lock to send a request.

In addition , if you just want a user just send request in a low frequency，like 1 time/10s。You can declare a variable to keep last time the request sent, and every time check the duration between the last execute time and current time.