Использование блокировок, когда вам это не нужно, замедлит работу вашего приложения. Это может быть слишком мало для измерения или может быть удивительно высоким.
ИМХО Зачастую лучшим подходом является использование кода без блокировки в однопоточной программе, чтобы было ясно, что этот код не предназначен для совместного использования в потоке. Это может быть более важным для обслуживания, чем любые проблемы с производительностью.
public static void main(String... args) throws IOException {
for (int i = 0; i < 3; i++) {
perfTest(new Vector<Integer>());
perfTest(new ArrayList<Integer>());
}
}
private static void perfTest(List<Integer> objects) {
long start = System.nanoTime();
final int runs = 100000000;
for (int i = 0; i < runs; i += 20) {
// add items.
for (int j = 0; j < 20; j+=2)
objects.add(i);
// remove from the end.
while (!objects.isEmpty())
objects.remove(objects.size() - 1);
}
long time = System.nanoTime() - start;
System.out.printf("%s each add/remove took an average of %.1f ns%n", objects.getClass().getSimpleName(), (double) time/runs);
}
печать
Vector each add/remove took an average of 38.9 ns
ArrayList each add/remove took an average of 6.4 ns
Vector each add/remove took an average of 10.5 ns
ArrayList each add/remove took an average of 6.2 ns
Vector each add/remove took an average of 10.4 ns
ArrayList each add/remove took an average of 5.7 ns
С точки зрения производительности, если для вас важны 4 нс, вы должны использовать несинхронизированную версию.
Для 99% случаев ясность кода важнее производительности. Ясный, простой код часто также работает достаточно хорошо.
Кстати: я использую 4,6 ГГц i7 2600 с Oracle Java 7u1.
Для сравнения, если я сделаю следующее, где perfTest1,2,3 идентичны.
perfTest1(new ArrayList<Integer>());
perfTest2(new Vector<Integer>());
perfTest3(Collections.synchronizedList(new ArrayList<Integer>()));
Я получаю
ArrayList each add/remove took an average of 2.6 ns
Vector each add/remove took an average of 7.5 ns
SynchronizedRandomAccessList each add/remove took an average of 8.9 ns
Если я использую общий метод perfTest, он не может встроить код так оптимально, и все они медленнее
ArrayList each add/remove took an average of 9.3 ns
Vector each add/remove took an average of 12.4 ns
SynchronizedRandomAccessList each add/remove took an average of 13.9 ns
Смена порядка тестов
ArrayList each add/remove took an average of 3.0 ns
Vector each add/remove took an average of 39.7 ns
ArrayList each add/remove took an average of 2.0 ns
Vector each add/remove took an average of 4.6 ns
ArrayList each add/remove took an average of 2.3 ns
Vector each add/remove took an average of 4.5 ns
ArrayList each add/remove took an average of 2.3 ns
Vector each add/remove took an average of 4.4 ns
ArrayList each add/remove took an average of 2.4 ns
Vector each add/remove took an average of 4.6 ns
по одному
ArrayList each add/remove took an average of 3.0 ns
ArrayList each add/remove took an average of 3.0 ns
ArrayList each add/remove took an average of 2.3 ns
ArrayList each add/remove took an average of 2.2 ns
ArrayList each add/remove took an average of 2.4 ns
и
Vector each add/remove took an average of 28.4 ns
Vector each add/remove took an average of 37.4 ns
Vector each add/remove took an average of 7.6 ns
Vector each add/remove took an average of 7.6 ns
Vector each add/remove took an average of 7.6 ns