Bulk operations

Definition

ConcurrentHashMap has bulk methods that can run in parallel: forEach, search and reduce. You give a parallelism threshold: the map only splits the work across threads when it is bigger than that number.

Example code

Totalling and searching a map in parallel

import java.util.concurrent.ConcurrentHashMap;

class Demo {
    public static void main(String[] args) {
        ConcurrentHashMap<String, Integer> sales = new ConcurrentHashMap<>();
        sales.put("north", 120);
        sales.put("south", 80);
        sales.put("east", 200);
        sales.put("west", 50);

        long threshold = 1;                                           // 1 = use as much parallelism as possible

        int total = sales.reduceValues(threshold, Integer::sum);      // combine all values
        System.out.println("total: " + total);

        String bigRegion = sales.search(threshold, (region, amount) -> amount > 150 ? region : null);
        System.out.println("over 150: " + bigRegion);

        long count = sales.reduceValuesToLong(threshold, v -> 1L, 0L, Long::sum);
        System.out.println("regions: " + count);
    }
}

// Output:
// total: 450
// over 150: east
// regions: 4