JUC atomic accumulator

JUC Atomic accumulator

Accumulator performance comparison

private static <T> void demo(Supplier<T> adderSupplier, Consumer<T> action) {
    
 T adder = adderSupplier.get();
 long start = System.nanoTime();
 List<Thread> ts = new ArrayList<>();
 // 4  Threads , Everyone adds up  50  ten thousand 
 for (int i = 0; i < 40; i++) {
    
 ts.add(new Thread(() -> {
    
 for (int j = 0; j < 500000; j++) {
    
 action.accept(adder);
 }
 }));
 }
 ts.forEach(t -> t.start());
 ts.forEach(t -> {
    
 try {
    
 t.join();
 } catch (InterruptedException e) {
    
 e.printStackTrace();
 }
 });
 long end = System.nanoTime();
 System.out.println(adder + " cost:" + (end - start)/1000_000);
}

Compare AtomicLong And LongAdder

for (int i = 0; i < 5; i++) {
    
 demo(() -> new LongAdder(), adder -> adder.increment());
}
for (int i = 0; i < 5; i++) {
    
 demo(() -> new AtomicLong(), adder -> adder.getAndIncrement());
}

Output

1000000 cost:43 
1000000 cost:9 
1000000 cost:7 
1000000 cost:7 
1000000 cost:7 

1000000 cost:31 
1000000 cost:27 
1000000 cost:28 
1000000 cost:24 
1000000 cost:22

The reason for the performance improvement is simple , It's when there's competition , Set multiple accumulation units ,Therad-0 Add up Cell[0], and Thread-1 Add up Cell[1]… Finally, summarize the results . In this way, they operate differently when accumulating Cell Variable , Therefore, it is reduced CAS Retry fail , To improve performance .