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测试利用if + switch来提高分支预测准确性,对比纯switch的效率
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import java.util.Date; | |
import java.util.Random; | |
import org.openjdk.jmh.annotations.Benchmark; | |
import org.openjdk.jmh.annotations.BenchmarkMode; | |
import org.openjdk.jmh.annotations.Fork; | |
import org.openjdk.jmh.annotations.Mode; | |
import org.openjdk.jmh.annotations.Param; | |
import org.openjdk.jmh.annotations.Scope; | |
import org.openjdk.jmh.annotations.Setup; | |
import org.openjdk.jmh.annotations.State; | |
import org.openjdk.jmh.infra.Blackhole; | |
public class TestBenchMarks { | |
public enum ChannelState { | |
CONNECTED, DISCONNECTED, SENT, RECEIVED, CAUGHT | |
} | |
@State(Scope.Benchmark) | |
public static class ExecutionPlan { | |
@Param({ "1000000" }) | |
public int size; | |
public ChannelState[] states = null; | |
@Setup | |
public void setUp() { | |
ChannelState[] values = ChannelState.values(); | |
states = new ChannelState[size]; | |
Random random = new Random(new Date().getTime()); | |
for (int i = 0; i < size; i++) { | |
int nextInt = random.nextInt(1000000); | |
if (nextInt > 100) { | |
states[i] = ChannelState.RECEIVED; | |
} else { | |
states[i] = values[nextInt % values.length]; | |
} | |
} | |
} | |
} | |
@Fork(value = 5) | |
@Benchmark | |
@BenchmarkMode(Mode.Throughput) | |
public void benchSiwtch(ExecutionPlan plan, Blackhole bh) { | |
int result = 0; | |
for (int i = 0; i < plan.size; ++i) { | |
switch (plan.states[i]) { | |
case CONNECTED: | |
result += ChannelState.CONNECTED.ordinal(); | |
break; | |
case DISCONNECTED: | |
result += ChannelState.DISCONNECTED.ordinal(); | |
break; | |
case SENT: | |
result += ChannelState.SENT.ordinal(); | |
break; | |
case RECEIVED: | |
result += ChannelState.RECEIVED.ordinal(); | |
break; | |
case CAUGHT: | |
result += ChannelState.CAUGHT.ordinal(); | |
break; | |
} | |
} | |
bh.consume(result); | |
} | |
@Fork(value = 5) | |
@Benchmark | |
@BenchmarkMode(Mode.Throughput) | |
public void benchIfAndSwitch(ExecutionPlan plan, Blackhole bh) { | |
int result = 0; | |
for (int i = 0; i < plan.size; ++i) { | |
ChannelState state = plan.states[i]; | |
if (state == ChannelState.RECEIVED) { | |
result += ChannelState.RECEIVED.ordinal(); | |
} else { | |
switch (state) { | |
case CONNECTED: | |
result += ChannelState.CONNECTED.ordinal(); | |
break; | |
case SENT: | |
result += ChannelState.SENT.ordinal(); | |
break; | |
case DISCONNECTED: | |
result += ChannelState.DISCONNECTED.ordinal(); | |
break; | |
case CAUGHT: | |
result += ChannelState.CAUGHT.ordinal(); | |
break; | |
} | |
} | |
} | |
bh.consume(result); | |
} | |
} |
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实际统计发现,state绝大部分情况都是
RECEIVED
,统计结果是: