Java线程转储CPU还是只等待IO？

Question

我复制了一个可疑的线程转储。在调用java.net.SocketInputStream.socketRead0()时，我看到173个线程处于IN_NATIVE状态，而在同一个调用中，有30个线程处于阻塞状态。

我认为阻塞状态不会消耗CPU，但它们正在等待IO。

那么处于IN_NATIVE状态的线程呢？他们是否消耗CPU？你知道为什么我在同一个socketRead0()调用中看到不同的线程状态吗？

173 threads
Thread 40283 - threadId:Thread 40283 - state:IN_NATIVE
stackTrace:
java.net.SocketInputStream.socketRead0(java.io.FileDescriptor, byte[], int, int, int) @bci=0 (Compiled frame; information may be imprecise)
java.net.SocketInputStream.read(byte[], int, int, int) @bci=87, line=152 (Compiled frame)
java.net.SocketInputStream.read(byte[], int, int) @bci=11, line=122 (Compiled frame)
com.sun.mail.util.TraceInputStream.read(byte[], int, int) @bci=7, line=110 (Compiled frame)
java.io.BufferedInputStream.fill() @bci=175, line=235 (Compiled frame)
java.io.BufferedInputStream.read() @bci=12, line=254 (Compiled frame)
com.sun.mail.util.LineInputStream.readLine() @bci=33, line=88 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.readServerResponse() @bci=43, line=1589 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.openServer(java.lang.String, int) @bci=117, line=1369 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.protocolConnect(java.lang.String, int, java.lang.String, java.lang.String) @bci=270, line=412 (Compiled frame)
javax.mail.Service.connect(java.lang.String, int, java.lang.String, java.lang.String) @bci=380, line=288 (Compiled frame)
com.healthies.push.injectors.mailsenders.DefaultMailSender.sendMessage(com.healthies.push.messages.EmailMessage, javax.mail.internet.MimeMessage) @bci=28, line=63 (Compiled frame)
com.healthies.push.injectors.SMTPMessageInjector.sendMessage(com.healthies.push.injectors.mailsenders.MailSender, com.healthies.push.messages.EmailMessage, javax.mail.internet.MimeMessage) @bci=55, line=140 (Compiled frame)
com.healthies.push.injectors.SMTPMessageInjector.inject(com.healthies.push.messages.EmailMessage) @bci=210, line=117 (Compiled frame)
com.healthies.push.injectors.SMTPMessageInjector.inject(com.healthies.push.messages.Message) @bci=5, line=35 (Compiled frame)
com.healthies.push.injectors.EmailInjectorPool$1.run() @bci=85, line=40 (Compiled frame)
java.util.concurrent.Executors$RunnableAdapter.call() @bci=4, line=471 (Compiled frame)
java.util.concurrent.FutureTask.run() @bci=42, line=262 (Compiled frame)
java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=95, line=1145 (Compiled frame)
java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=5, line=615 (Interpreted frame)
java.lang.Thread.run() @bci=11, line=745 (Interpreted frame)
--------------------------------------------------------------------
30 threads 
Thread 40276 - threadId:Thread 40276 - state:BLOCKED
stackTrace:
java.net.SocketInputStream.socketRead0(java.io.FileDescriptor, byte[], int, int, int) @bci=0 (Compiled frame; information may be imprecise)
java.net.SocketInputStream.read(byte[], int, int, int) @bci=87, line=152 (Compiled frame)
java.net.SocketInputStream.read(byte[], int, int) @bci=11, line=122 (Compiled frame)
com.sun.mail.util.TraceInputStream.read(byte[], int, int) @bci=7, line=110 (Compiled frame)
java.io.BufferedInputStream.fill() @bci=175, line=235 (Compiled frame)
java.io.BufferedInputStream.read() @bci=12, line=254 (Compiled frame)
com.sun.mail.util.LineInputStream.readLine() @bci=33, line=88 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.readServerResponse() @bci=43, line=1589 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.issueSendCommand(java.lang.String, int) @bci=6, line=1494 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.finishData() @bci=34, line=1321 (Compiled frame)
com.sun.mail.smtp.SMTPTransport.sendMessage(javax.mail.Message, javax.mail.Address[]) @bci=281, line=637 (Compiled frame)
com.healthies.push.injectors.mailsenders.DefaultMailSender.sendMessage(com.healthies.push.messages.EmailMessage, javax.mail.internet.MimeMessage) @bci=37, line=64 (Compiled frame)
com.healthies.push.injectors.SMTPMessageInjector.sendMessage(com.healthies.push.injectors.mailsenders.MailSender, com.healthies.push.messages.EmailMessage, javax.mail.internet.MimeMessage) @bci=55, line=140 (Compiled frame)
com.healthies.push.injectors.SMTPMessageInjector.inject(com.healthies.push.messages.EmailMessage) @bci=210, line=117 (Compiled frame)
com.healthies.push.injectors.SMTPMessageInjector.inject(com.healthies.push.messages.Message) @bci=5, line=35 (Compiled frame)
com.healthies.push.injectors.EmailInjectorPool$1.run() @bci=85, line=40 (Compiled frame)
java.util.concurrent.Executors$RunnableAdapter.call() @bci=4, line=471 (Compiled frame)
java.util.concurrent.FutureTask.run() @bci=42, line=262 (Compiled frame)
java.util.concurrent.ThreadPoolExecutor.runWorker(java.util.concurrent.ThreadPoolExecutor$Worker) @bci=95, line=1145 (Compiled frame)
java.util.concurrent.ThreadPoolExecutor$Worker.run() @bci=5, line=615 (Interpreted frame)
java.lang.Thread.run() @bci=11, line=745 (Interpreted frame)

Answer 1

通常，您永远不会看到线程在BLOCKED状态下执行非同步的本机方法。但是这个转储是在强制模式(jstack -F)下获得的，这种模式是works differently。

看起来JVM已经请求了一个safepoint operation。所有运行Java代码的线程都必须在安全点处停止，但本机方法仍然可以运行。每当本机方法返回时，它都会检查安全点操作是否正在进行，如果正在进行，则会阻塞当前线程，直到VM操作完成。

所以，在你的情况下

处于BLOCKED状态的

• 线程已经完成了本机调用，并在从BLOCKED in IN_NATIVE状态返回时等待安全点操作的结束。

仍在执行本机调用，该调用可能在套接字读取时被阻塞。

JVM无法区分系统调用上阻塞的本机方法和实际消耗CPU的本机方法--在这两种情况下，它都会显示处于IN_NATIVE状态的线程。无论这些线程是否繁忙，都不能从线程转储中得出结论。

为了查看本机方法是否消耗CPU，您需要一个实用程序，如top、perf或native code aware profiler。