java 锁竞争_Java 9（JEP 143）中针对竞争锁的优化
在JEP 143(http://openjdk.java.net/jeps/143 在Java 9发布)中对竞争锁做了优化，简要内容如下：
JEP 143: Improve Contended Locking
Summary: Improve the performance of contended Java object monitors.
做一个简单的对比测试，代码如下，分别基于Java 8.0_152和Java 9.0.4
按照官方说明，关闭偏向锁和轻量锁 -XX:-UseBiasedLocking -XX:+UseHeavyMonitors
public class SyncTest implements Runnable {
public static void main(String[] args) throws InterruptedException {
int threadNum = 4;
SyncTest syncTest = new SyncTest();
Thread[] threadGroup = new Thread[threadNum];
for (int i = 0; i < threadNum; i++) {
threadGroup[i] = new Thread(syncTest);
}
long begin = System.currentTimeMillis();
for (int i = 0; i < threadNum; i++) {
threadGroup[i].start();
}
for (int i = 0; i < threadNum; i++) {
threadGroup[i].join();
}
long end = System.currentTimeMillis();
System.out.println(end - begin);
}
public void run() {
for (int i = 0; i < 100000000; i++) {
synchronized (this) {
}
}
}
}
最终经过多次对比：
在Java8下，平均执行时间大约为5.8s
在Java9下，平均执行时间大约为4.4s
在JEP 143(http://openjdk.java.net/jeps/143 在Java 9发布)中对竞争锁做了优化，简要内容如下： JEP 143: Improve Contended Locking Summary: Improve the performance of contended Java object monitors. 做一个简单的对比测试，代码如下，分别基于Java 8.0_152和Java 9.0.4 按照官方说明，关闭偏向锁和轻量锁 -XX:-UseBiasedLocking -XX:+UseHeavyMonitors public class SyncTest implements Runnable { public static void main(String[] args) throws InterruptedException { int threadNum = 4; SyncTest syncTest = new SyncTest(); Thread[] threadGroup = new Thread[threadNum]; for (int i = 0; i < threadNum; i++) { threadGroup[i] = new Thread(syncTest); } long begin = System.currentTimeMillis(); for (int i = 0; i < threadNum; i++) { threadGroup[i].start(); } for (int i = 0; i < threadNum; i++) { threadGroup[i].join(); } long end = System.currentTimeMillis(); System.out.println(end - begin); } public void run() { for (int i = 0; i < 100000000; i++) { synchronized (this) { } } } } 最终经过多次对比： 在Java8下，平均执行时间大约为5.8s 在Java9下，平均执行时间大约为4.4s