一、java中的thread狀態

java中呼叫VM.toThreadState()計算執行緒狀態

VM.class

public static State toThreadState(int var0) {
        if ((var0 & 4) != 0) {
            return State.RUNNABLE;
        } else if ((var0 & 1024) != 0) {
            return State.BLOCKED;
        } else if ((var0 & 16) != 0) {
            return State.WAITING;
        } else if ((var0 & 32) != 0) {
            return State.TIMED_WAITING;
        } else if ((var0 & 2) != 0) {
            return State.TERMINATED;
        } else {
            return (var0 & 1) == 0 ? State.NEW : State.RUNNABLE;
        }
    }
 

二、java中的thread的狀態對應的jvm中的狀態

jvm中執行緒狀態的定義如下：

/hotspot/src/share/classfile/javaClasses.hpp

// Java Thread Status for JVMTI and M&M use.
  // This thread status info is saved in threadStatus field of
  // java.lang.Thread java class.
  enum ThreadStatus {
    NEW                      = 0,
    RUNNABLE                 = JVMTI_THREAD_STATE_ALIVE +          // runnable / running
                               JVMTI_THREAD_STATE_RUNNABLE,
    SLEEPING                 = JVMTI_THREAD_STATE_ALIVE +          // Thread.sleep()
                               JVMTI_THREAD_STATE_WAITING +
                               JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT +
                               JVMTI_THREAD_STATE_SLEEPING,
    IN_OBJECT_WAIT           = JVMTI_THREAD_STATE_ALIVE +          // Object.wait()
                               JVMTI_THREAD_STATE_WAITING +
                               JVMTI_THREAD_STATE_WAITING_INDEFINITELY +
                               JVMTI_THREAD_STATE_IN_OBJECT_WAIT,
    IN_OBJECT_WAIT_TIMED     = JVMTI_THREAD_STATE_ALIVE +          // Object.wait(long)
                               JVMTI_THREAD_STATE_WAITING +
                               JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT +
                               JVMTI_THREAD_STATE_IN_OBJECT_WAIT,
    PARKED                   = JVMTI_THREAD_STATE_ALIVE +          // LockSupport.park()
                               JVMTI_THREAD_STATE_WAITING +
                               JVMTI_THREAD_STATE_WAITING_INDEFINITELY +
                               JVMTI_THREAD_STATE_PARKED,
    PARKED_TIMED             = JVMTI_THREAD_STATE_ALIVE +          // LockSupport.park(long)
                               JVMTI_THREAD_STATE_WAITING +
                               JVMTI_THREAD_STATE_WAITING_WITH_TIMEOUT +
                               JVMTI_THREAD_STATE_PARKED,
    BLOCKED_ON_MONITOR_ENTER = JVMTI_THREAD_STATE_ALIVE +          // (re-)entering a synchronization block
                               JVMTI_THREAD_STATE_BLOCKED_ON_MONITOR_ENTER,
    TERMINATED               = JVMTI_THREAD_STATE_TERMINATED
  };
 

看完上面程式碼之後就能理解在VM.class中為什麼用位與的方式來計算執行緒狀態。

jvm中設定java執行緒狀態的方法如下：

// Write thread status info to threadStatus field of java.lang.Thread.
  static void set_thread_status(oop java_thread_oop, ThreadStatus status);

三、jvm中c++執行緒的狀態

/hotspot/src/share/vm/utilities/globalDefinitions.hpp

// JavaThreadState keeps track of which part of the code a thread is executing in. This
// information is needed by the safepoint code.
//
// There are 4 essential states:
//
//  _thread_new         : Just started, but not executed init. code yet (most likely still in OS init code)
//  _thread_in_native   : In native code. This is a safepoint region, since all oops will be in jobject handles
//  _thread_in_vm       : Executing in the vm
//  _thread_in_Java     : Executing either interpreted or compiled Java code (or could be in a stub)
//
// Each state has an associated xxxx_trans state, which is an intermediate state used when a thread is in
// a transition from one state to another. These extra states makes it possible for the safepoint code to
// handle certain thread_states without having to suspend the thread - making the safepoint code faster.
//
// Given a state, the xxx_trans state can always be found by adding 1.
//
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
};
 

從註釋來看，“安全點需要這些資訊”。

其中主要的狀態是這5種:

_thread_new: 新建立的執行緒

_thread_in_Java: 在執行Java程式碼

_thread_in_vm: 在執行JVM本身的程式碼

_thread_in_native: 在執行native程式碼

_thread_blocked: 執行緒被阻塞了，包括等待一個鎖，等待一個條件，sleep，執行一個阻塞的IO等

四、os中執行緒的狀態

/hotspot/src/share/vm/runtime/osThread.hpp

// The OSThread class holds OS-specific thread information.  It is equivalent
// to the sys_thread_t structure of the classic JVM implementation.

// The thread states represented by the ThreadState values are platform-specific
// and are likely to be only approximate, because most OSes don't give you access
// to precise thread state information.

// Note: the ThreadState is legacy code and is not correctly implemented.
// Uses of ThreadState need to be replaced by the state in the JavaThread.

enum ThreadState {
  ALLOCATED,                    // Memory has been allocated but not initialized
  INITIALIZED,                  // The thread has been initialized but yet started
  RUNNABLE,                     // Has been started and is runnable, but not necessarily running
  MONITOR_WAIT,                 // Waiting on a contended monitor lock
  CONDVAR_WAIT,                 // Waiting on a condition variable
  OBJECT_WAIT,                  // Waiting on an Object.wait() call
  BREAKPOINTED,                 // Suspended at breakpoint
  SLEEPING,                     // Thread.sleep()
  ZOMBIE                        // All done, but not reclaimed yet
};

比較常見有:

Runnable: 可以執行或者正在執行的

MONITOR_WAIT: 等待鎖

OBJECT_WAIT: 執行了Object.wait()之後在條件佇列中等待的

SLEEPING: 執行了Thread.sleep()的