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本文主要研究一下如何在应用代码里捕获线程堆栈
getRunnableStackTraces
org/h2/util/Profiler.java
代码语言：javascript复制 private static List<Object[]> getRunnableStackTraces() {
ArrayList<Object[]> list = new ArrayList<>();
Map<Thread, StackTraceElement[]> map = Thread.getAllStackTraces();
for (Map.Entry<Thread, StackTraceElement[]> entry : map.entrySet()) {
Thread t = entry.getKey();
if (t.getState() != Thread.State.RUNNABLE) {
continue;
}
StackTraceElement[] dump = entry.getValue();
if (dump == null || dump.length == 0) {
continue;
}
list.add(dump);
}
return list;
}h2的Profiler的getRunnableStackTraces方法通过Thread.getAllStackTraces()来收集线程堆栈
readRunnableStackTraces
org/h2/util/Profiler.java
代码语言：javascript复制 private static List<Object[]> readRunnableStackTraces(int pid) {
try {
String jstack = exec("jstack", Integer.toString(pid));
LineNumberReader r = new LineNumberReader(
new StringReader(jstack));
return readStackTrace(r);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
private static String exec(String... args) {
ByteArrayOutputStream err = new ByteArrayOutputStream();
ByteArrayOutputStream out = new ByteArrayOutputStream();
try {
Process p = Runtime.getRuntime().exec(args);
copyInThread(p.getInputStream(), out);
copyInThread(p.getErrorStream(), err);
p.waitFor();
String e = new String(err.toByteArray(), StandardCharsets.UTF_8);
if (e.length() > 0) {
throw new RuntimeException(e);
}
return new String(out.toByteArray(), StandardCharsets.UTF_8);
} catch (Exception e) {
throw new RuntimeException(e);
}
} h2的Profiler的readRunnableStackTraces方法则是基于给定的pid使用jstack来捕获线程堆栈
CommandProcessor
sun/jvm/hotspot/CommandProcessor.java
代码语言：javascript复制new Command("jstack", "jstack [-v]", false) {
public void doit(Tokens t) {
boolean verbose = false;
if (t.countTokens() > 0 && t.nextToken().equals("-v")) {
verbose = true;
}
StackTrace jstack = new StackTrace(verbose, true);
jstack.run(out);
}
}sun.jvm.hotspot包的CommandProcessor提供了对jstack的支持
ThreadDumpEndpoint
org/springframework/boot/actuate/management/ThreadDumpEndpoint.java
代码语言：javascript复制 @ReadOperation(produces = "text/plain;charset=UTF-8")
public String textThreadDump() {
return getFormattedThreadDump(this.plainTextFormatter::format);
}
private <T> T getFormattedThreadDump(Function<ThreadInfo[], T> formatter) {
return formatter.apply(ManagementFactory.getThreadMXBean().dumpAllThreads(true, true));
} springboot的ThreadDumpEndpoint则使用的是ManagementFactory.getThreadMXBean().dumpAllThreads来获取线程堆栈
小结
在java运行时可以通过Thread.getAllStackTraces()、ManagementFactory.getThreadMXBean().dumpAllThreads来获取当前进程的线程堆栈信息，也可以通过Process调用jstack命令，值得注意的是jstack捕获的线程堆栈包含了nid(比如"C2 CompilerThread0" #7 daemon prio=9 os_prio=31 cpu=481.27ms elapsed=36.74s tid=0x00007fb08c068400 nid=0x6803 waiting on condition [0x0000000000000000])，也就是top -H -p pid中展示的PID信息，而前面两个方法dump出来的没有nid这个信息。
