Q. What output is expected from the following code? What does it actually output?
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import java.util.Collections; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public final class WhatIsWrong implements Runnable { private Map<String, Integer> myMap = null; public WhatIsWrong(Map<String, Integer> myMap) { this.myMap = myMap; } public static void main(String[] args) throws InterruptedException { long start = System.currentTimeMillis(); Map<String, Integer> myMap = Collections.synchronizedMap(new HashMap<String, Integer>()); for (int i = 1; i <= 10; i++) { myMap.put("Key-" + i, i); // 10 items in the map } // process 1 million times with 20 threads ExecutorService threadPool = Executors.newFixedThreadPool(20); for (int i = 1; i <= 1000000; i++) { WhatIsWrong wiw = new WhatIsWrong(myMap); threadPool.submit(wiw); //submit 1 million tasks to the thread pool } threadPool.shutdown(); threadPool.awaitTermination(60, TimeUnit.SECONDS); traverseAndPrint(myMap); long finish = System.currentTimeMillis(); System.out.println("Processed in " + (finish - start) + " ms"); } @Override public void run() { traverseAndUpdate(); } private void traverseAndUpdate() { Iterator<String> it = myMap.keySet().iterator(); while (it.hasNext()) { String key = it.next(); Integer newValue = this.myMap.get(key) + 1; myMap.put(key, newValue); } } private static void traverseAndPrint(Map<String, Integer> myMap) { Iterator<String> it = myMap.keySet().iterator(); while (it.hasNext()) { String key = it.next(); System.out.println(key + " = " + myMap.get(key)); } } } |
A. It is expected to output counts from 100,001 to 100,010, but actually the output will be as shown below missing counts. Output with missing…
