本文共 4598 字，大约阅读时间需要 15 分钟。

代码：

import java.util.concurrent.TimeUnit;import java.util.concurrent.atomic.AtomicReference;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;import org.openjdk.jmh.annotations.Benchmark;import org.openjdk.jmh.annotations.BenchmarkMode;import org.openjdk.jmh.annotations.Group;import org.openjdk.jmh.annotations.GroupThreads;import org.openjdk.jmh.annotations.Measurement;import org.openjdk.jmh.annotations.Mode;import org.openjdk.jmh.annotations.OutputTimeUnit;import org.openjdk.jmh.annotations.Scope;import org.openjdk.jmh.annotations.State;import org.openjdk.jmh.annotations.Warmup;import org.openjdk.jmh.profile.StackProfiler;import org.openjdk.jmh.runner.Runner;import org.openjdk.jmh.runner.RunnerException;import org.openjdk.jmh.runner.options.Options;import org.openjdk.jmh.runner.options.OptionsBuilder;import org.openjdk.jmh.runner.options.TimeValue;@Measurement(iterations=5)@Warmup(iterations=5)@BenchmarkMode(Mode.AverageTime)@OutputTimeUnit(TimeUnit.MICROSECONDS)@State(Scope.Group)public class AtomicRefTest {		private volatile AtomicReference
   
     ar=new AtomicReference<>(new CustomerInfo("FangZhang",0));	private volatile CustomerInfo ci=new CustomerInfo("ZhiZhang",0);	private volatile CustomerInfo lci=new CustomerInfo("FanJian",0);	private final Lock lock=new ReentrantLock();		public static class CustomerInfo{		private final String name;		private  int moralIntegrityValue=0;				public CustomerInfo(String name,int moralIntegrityValue) {			this.name=name;			this.moralIntegrityValue=moralIntegrityValue;		}				public String getName() {			return name;		}		public int getMoralIntegrityValue() {			return moralIntegrityValue;		}		public void setMoralIntegrityValue(int moralIntegrityValue) {			this.moralIntegrityValue = moralIntegrityValue;		}				}		@GroupThreads(10)	@Group("sync")	@Benchmark	public void syncCI() {		synchronized(this) {			ci.setMoralIntegrityValue(ci.getMoralIntegrityValue()+1);		}	}		@GroupThreads(10)	@Group("lock")	@Benchmark	public void lockCI() {		lock.lock();		try {			lci.setMoralIntegrityValue(lci.getMoralIntegrityValue()+1);		}finally {			lock.unlock();		}	}		@GroupThreads(10)	@Group("atom")	@Benchmark	public void atomCI() {		final CustomerInfo c=ar.get();		CustomerInfo newCI=new CustomerInfo(c.getName(),c.getMoralIntegrityValue()+1);		ar.compareAndSet(c, newCI);	}			public static void main(String[] args) {		Options opt=new OptionsBuilder()		        .include(AtomicRefTest.class.getSimpleName())		        .forks(1)		        .timeout(TimeValue.seconds(10))		        .addProfiler(StackProfiler.class)		        .build();		try {			new Runner(opt).run();		} catch (RunnerException e) {			// TODO Auto-generated catch block			e.printStackTrace();		}	}}
   

测试结果：

Result "jmhtest.AtomicRefTest.atom":  0.234 ±(99.9%) 0.021 us/op [Average]  (min, avg, max) = (0.226, 0.234, 0.241), stdev = 0.006  CI (99.9%): [0.212, 0.255] (assumes normal distribution)Secondary result "jmhtest.AtomicRefTest.atom:·stack":Stack profiler:....[Thread state distributions].................................................................... 90.0%         RUNNABLE  9.1%         TIMED_WAITING  0.9%         WAITINGResult "jmhtest.AtomicRefTest.lock":  0.203 ±(99.9%) 0.009 us/op [Average]  (min, avg, max) = (0.201, 0.203, 0.207), stdev = 0.002  CI (99.9%): [0.195, 0.212] (assumes normal distribution)Secondary result "jmhtest.AtomicRefTest.lock:·stack":Stack profiler:....[Thread state distributions].................................................................... 78.9%         WAITING 12.0%         RUNNABLE  9.1%         TIMED_WAITINGResult "jmhtest.AtomicRefTest.sync":  0.282 ±(99.9%) 0.066 us/op [Average]  (min, avg, max) = (0.253, 0.282, 0.295), stdev = 0.017  CI (99.9%): [0.216, 0.347] (assumes normal distribution)Secondary result "jmhtest.AtomicRefTest.sync:·stack":Stack profiler:....[Thread state distributions].................................................................... 69.8%         BLOCKED 21.0%         RUNNABLE  9.1%         TIMED_WAITINGBenchmark                  Mode  Cnt  Score   Error  UnitsAtomicRefTest.atom         avgt    5  0.234 ± 0.021  us/opAtomicRefTest.atom:·stack  avgt         NaN            ---AtomicRefTest.lock         avgt    5  0.203 ± 0.009  us/opAtomicRefTest.lock:·stack  avgt         NaN            ---AtomicRefTest.sync         avgt    5  0.282 ± 0.066  us/opAtomicRefTest.sync:·stack  avgt         NaN            ---

运行结果分析：

1、单纯从同步速度来看，lock方式的同步效率最高，其次是原子引用的方式，最后是synchronized的方式。

2、原子引用的方式虽然是非阻塞的方式，但是同步时的操作步骤明显要比其余两种方式要多，也正是因为步骤多，拖累了同步的运行效率。

3、多次运行后，统计结果仍然符合这种运行规律。

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