这篇文章主要介绍“jvm线程变化是怎样的”，在日常操作中，相信很多人在jvm线程变化是怎样的问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”jvm线程变化是怎样的”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
jvm线程是维护了线程的状态。new，running，waiting，timed waiting，blocked，terminated。我们通过jstack等工具查看的时候，线程状态就是上面的一种。jvm本身是做了一种抽象，我们现在从一个典型的方法，来跟踪查看一下jvm内部又是怎么做状态变化的。
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public static native void sleep(long millis) throws InterruptedException;sleep是一个native 方法，我们通过jvm原来来进行跟着（源码来自openjdk11)。根据jni的规范，我们通过包名或者是jni的注册方式找到了对应的声明。
static JNINativeMethod methods[] = { {"start0",
"()V", (void *)&JVM_StartThread}, {"stop0", "(" OBJ
")V", (void *)&JVM_StopThread}, {"isAlive", "()Z", (void *)&JVM_IsThreadAlive}, {"suspend0",
"()V", (void *)&JVM_SuspendThread}, {"resume0", "()V", (void *)&JVM_ResumeThread}, {"setPriority0",
"(I)V", (void *)&JVM_SetThreadPriority}, {"yield", "()V", (void *)&JVM_Yield}, {"sleep", "(J)V", (void *)&JVM_Sleep}, {"currentThread", "()" THD, (void *)&JVM_CurrentThread}, {"countStackFrames",
"()I", (void *)&JVM_CountStackFrames}, {"interrupt0",
"()V", (void *)&JVM_Interrupt}, {"isInterrupted", "(Z)Z", (void *)&JVM_IsInterrupted}, {"holdsLock", "(" OBJ
")Z", (void *)&JVM_HoldsLock}, {"getThreads", "()[" THD, (void *)&JVM_GetAllThreads}, {"dumpThreads", "([" THD
")[[" STE, (void *)&JVM_DumpThreads}, {"setNativeName", "(" STR
")V", (void *)&JVM_SetNativeThreadName},};接下来我们要跟踪的就是JVM_Sleep了。我们一点一点来解析这个方法。首先这里有宏定义。
JVM_ENTRY(void, JVM_Sleep(JNIEnv* env, jclass threadClass, jlong millis))我们展开JVM_ENTRY。
#define JVM_ENTRY(result_type, header) \extern
"C" { \ result_type JNICALL header { \ JavaThread* thread=JavaThread::thread_from_jni_environment(env); \ ThreadInVMfromNative __tiv(thread); \ debug_only(VMNativeEntryWrapper __vew;) \ VM_ENTRY_BASE(result_type, header, thread)在ThreadInVMfromNative中，发生了一次线程状态的变更。
class ThreadInVMfromNative : public ThreadStateTransition { public: ThreadInVMfromNative(JavaThread* thread) : ThreadStateTransition(thread) { trans_from_native(_thread_in_vm); } ~ThreadInVMfromNative() { trans_and_fence(_thread_in_vm, _thread_in_native); }};在构造方法中把JavaThread的**thread->thread_state()**状态变为了_thread_in_vm。在析构函数中把状态改成了_thread_in_native。这里的__tiv是一个本地对象，只有在栈销毁的时候才会触发析构，也就是说这里的转为_thread_in_native只不过是一瞬间的事情。展开头结束后，我们再继续往后观察。
JavaThreadSleepState
jtss(thread);在这个构造方法中。把**java_thread->threadObj()**的状态变为了
java_lang_Thread::SLEEPING
static void set_thread_status(JavaThread*
java_thread, java_lang_Thread::ThreadStatus state) { java_lang_Thread::set_thread_status(java_thread->threadObj(), state); }这里对应的就是java的线程的状态了。在往下走就直接设置**thread->osthread()**的状态为sleep。
ThreadState old_state = thread->osthread()->get_state(); thread->osthread()->set_state(SLEEPING);状态到这里全部设置完成。
通过上面的代码，我们可以发现最核心的就是JavaThread的这个对象，他本身代表的jvm中的线程状态。会标识线程是在vm还是线程是在java或者在native。具体的状态如下
enum JavaThreadState { _thread_uninitialized
= 0, // should never happen (missing initialization) _thread_new
= 2, // just starting up, i.e., in process of being initialized _thread_new_trans
= 3, // corresponding transition state (not used, included for completness) _thread_in_native
= 4, // running in native code _thread_in_native_trans
= 5, // corresponding transition state _thread_in_vm
= 6, // running in VM _thread_in_vm_trans
= 7, // corresponding transition state _thread_in_Java
= 8, // running in Java or in stub code _thread_in_Java_trans
= 9, // corresponding transition state (not used, included for completness) _thread_blocked
= 10, // blocked in vm _thread_blocked_trans
= 11, // corresponding transition state _thread_max_state
= 12 // maximum thread state+1 - used for statistics allocation};这个类同时那种java线程状态的引用。就是java_thread->threadObj()。这个对应的是java的线程状态，这个也是我们jstack看到的状态。
"main" #1 prio=5 os_prio=31 tid=0x00007fee9b809000 nid=0xe03 waiting on condition [0x0000700008d65000] java.lang.Thread.State: TIMED_WAITING (sleeping) at java.lang.Thread.sleep(Native Method) at com.company.Sleep.main(Sleep.java:7)为什么输出的是timed_waiting(sleep)，这个主要是因为格式化输出的原因。
if(status == THREAD_STATUS_NEW){ return "NEW"; }else if(status == THREAD_STATUS_RUNNABLE){ return "RUNNABLE"; }else if(status == THREAD_STATUS_SLEEPING){ return "TIMED_WAITING (sleeping)"; }else if(status == THREAD_STATUS_IN_OBJECT_WAIT){ return "WAITING (on object monitor)"; }else if(status == THREAD_STATUS_IN_OBJECT_WAIT_TIMED){ return "TIMED_WAITING (on object monitor)"; }else if(status == THREAD_STATUS_PARKED){ return "WAITING (parking)"; }else if(status == THREAD_STATUS_PARKED_TIMED){ return "TIMED_WAITING (parking)"; }else if(status == THREAD_STATUS_BLOCKED_ON_MONITOR_ENTER){ return "BLOCKED (on object monitor)"; }else if(status == THREAD_STATUS_TERMINATED){ return "TERMINATED"; } return "UNKNOWN"; }在状态格式化的时候，把sleeping的归类成为TIMED_WAITING (sleeping)。于此同时Java Thread还拿着系统的线程thread->osthread()。
到此，关于“jvm线程变化是怎样的”的学习就结束了，希望能够解决大家的疑惑。理论与实践的搭配能更好的帮助大家学习，快去试试吧！若想继续学习更多相关知识，请继续关注亿速云网站，小编会继续努力为大家带来更多实用的文章！
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原文链接：http://blog.itpub.net/69923331/viewspace-2700930/
