Java 9 ea 中是否存在启动时间回归？
2022-09-04 21:39:58
我听说过
- JVM 随着每个主要版本而变得更快（在某些方面）
- 9的模块化将带来更快的启动时间。
为了加快Maven构建的速度，我下载并发现它需要更长的时间。此外，感觉在Maven开始之前有更长的延迟。jdk9-ea
我试图使用以下代码粗略地测量JVM启动时间
public class Sampler {
public static void main(String[] args) throws IOException, InterruptedException {
long t = System.currentTimeMillis();
if (args.length == 0 || args[0].startsWith("-")) {
sample(30, args);
} else {
long t0 = Long.parseLong(args[0]);
System.out.println(t - t0);
}
}
static void sample(int n, String[] options) throws IOException, InterruptedException {
File samples = new File("samples.txt");
for (int i = 0; i < n; i++) {
String javaPath = String.join(
System.getProperty("file.separator"),
System.getProperty("java.home"),
"bin",
"java");
List<String> command = new ArrayList<String>();
command.add(javaPath);
command.addAll(Arrays.asList(options));
command.add("Sampler");
command.add(Long.toString(System.currentTimeMillis()));
ProcessBuilder processBuilder = new ProcessBuilder(command)
.inheritIO()
.redirectOutput(ProcessBuilder.Redirect.appendTo(samples));
Process process = processBuilder.start();
process.waitFor();
}
prettyPrint(samples);
samples.delete();
}
...
}
从Java 9开始需要两倍的时间
>java -version java version "1.8.0_74" Java(TM) SE Runtime Environment (build 1.8.0_74-b02) Java HotSpot(TM) Client VM (build 25.74-b02, mixed mode, sharing) >javac Sampler.java && java Sampler n=30 units=milisec min=124 max=205 mean=143 median=132 >java -version java version "9-ea" Java(TM) SE Runtime Environment (build 9-ea+111) Java HotSpot(TM) Client VM (build 9-ea+111, mixed mode) >javac Sampler.java && java Sampler n=30 units=milisec min=279 max=387 mean=301 median=294 >javac Sampler.java && java Sampler -XX:+UseParallelGC n=30 units=milisec min=279 max=382 mean=297 median=292 >java -version java version "1.8.0_76-ea" Java(TM) SE Runtime Environment (build 1.8.0_76-ea-b04) Java HotSpot(TM) Client VM (build 25.76-b04, mixed mode, sharing) >javac Sampler.java && java Sampler n=30 units=milisec min=123 max=227 mean=159 median=141 >java Sampler -XX:+UseG1GC n=99 units=milisec min=188 max=340 mean=213 median=199
注意：最初我使用的是服务器虚拟机（x64），同样的2倍差距，Java9启动时间约为0.6秒。
后java -Xshare:dump
>java -version java version "9-ea" Java(TM) SE Runtime Environment (build 9-ea+111) Java HotSpot(TM) Client VM (build 9-ea+111, mixed mode, sharing) >javac Sampler.java && java Sampler n=50 units=milisec min=228 max=422 mean=269 median=269 >javac Sampler.java && java Sampler -Xshare:on <error messages> n=44 units=milisec min=227 max=392 mean=247 median=238 >javac Sampler.java && java Sampler -Xshare:off n=50 units=milisec min=280 max=513 mean=315 median=288 >javac Sampler.java && java Sampler -Xshare:auto n=50 units=milisec min=228 max=361 mean=283 median=285
使用 Java 8 ea
>java -Xshare:off Sampler n=99 units=milisec min=124 max=264 mean=150 median=136
错误信息：
An error has occurred while processing the shared archive file. Unable to map ReadOnly shared space at required address. Error occurred during initialization of VM Unable to use shared archive.
50个中的44个成功开始是我能得到的最高数字。最低为- 13。
