執行緒的狀態
Thread.State
首先看JDK中的程式碼: java.lang.Thread.State
/**
* A thread state.A thread can be in one of the following states:
* 一個執行緒的狀態，一個執行緒可以處於以下狀態中的某一個狀態
* <ul>
* <li>{@link #NEW}<br>
*A thread that has not yet started is in this state.
*</li>
* <li>{@link #RUNNABLE}<br>
*A thread executing in the Java virtual machine is in this state.
*</li>
* <li>{@link #BLOCKED}<br>
*A thread that is blocked waiting for a monitor lock
*is in this state.
*</li>
* <li>{@link #WAITING}<br>
*A thread that is waiting indefinitely for another thread to
*perform a particular action is in this state.
*</li>
* <li>{@link #TIMED_WAITING}<br>
*A thread that is waiting for another thread to perform an action
*for up to a specified waiting time is in this state.
*</li>
* <li>{@link #TERMINATED}<br>
*A thread that has exited is in this state.
*</li>
* </ul>
*
* <p>
* A thread can be in only one state at a given point in time.
* These states are virtual machine states which do not reflect
* any operating system thread states.
*
* @since1.5
* @see #getState
*/
public enum State {
/**
* Thread state for a thread which has not yet started.
*/
NEW,
/**
* Thread state for a runnable thread.A thread in the runnable
* state is executing in the Java virtual machine but it may
* be waiting for other resources from the operating system
* such as processor.
*/
RUNNABLE,
/**
* Thread state for a thread blocked waiting for a monitor lock.
* A thread in the blocked state is waiting for a monitor lock
* to enter a synchronized block/method or
* reenter a synchronized block/method after calling
* {@link Object#wait() Object.wait}.
*/
BLOCKED,
/**
* Thread state for a waiting thread.
* A thread is in the waiting state due to calling one of the
* following methods:
* <ul>
*<li>{@link Object#wait() Object.wait} with no timeout</li>
*<li>{@link #join() Thread.join} with no timeout</li>
*<li>{@link LockSupport#park() LockSupport.park}</li>
* </ul>
*
* <p>A thread in the waiting state is waiting for another thread to
* perform a particular action.
*
* For example, a thread that has called <tt>Object.wait()</tt>
* on an object is waiting for another thread to call
* <tt>Object.notify()</tt> or <tt>Object.notifyAll()</tt> on
* that object. A thread that has called <tt>Thread.join()</tt>
* is waiting for a specified thread to terminate.
*/
WAITING,
/**
* Thread state for a waiting thread with a specified waiting time.
* A thread is in the timed waiting state due to calling one of
* the following methods with a specified positive waiting time:
* <ul>
*<li>{@link #sleep Thread.sleep}</li>
*<li>{@link Object#wait(long) Object.wait} with timeout</li>
*<li>{@link #join(long) Thread.join} with timeout</li>
*<li>{@link LockSupport#parkNanos LockSupport.parkNanos}</li>
*<li>{@link LockSupport#parkUntil LockSupport.parkUntil}</li>
* </ul>
*/
TIMED_WAITING,
/**
* Thread state for a terminated thread.
* The thread has completed execution.
*/
TERMINATED;
}
1、新建(New)
新建立了一個執行緒物件，還未呼叫start()方法。
2、就緒（Runnable）
執行緒物件建立後，其他執行緒(比如main執行緒）呼叫了該物件的start()方法。該狀態的執行緒位於可執行執行緒池中，等待被執行緒排程選中 獲取cpu 的使用權 。
3、執行中（Running，執行緒狀態中並沒有這一狀態，但是實際執行中是有的）
可執行狀態(runnable)的執行緒獲得了cpu 時間片（timeslice） ，執行程式程式碼。
4、限期等待（Timed Waiting）
也可以稱作 TIMED_WAITING（有等待時間的等待狀態）。
執行緒主動呼叫以下方法：
Thread.sleep方法；
Object的wait方法，帶有時間；
Thread.join方法，帶有時間；
LockSupport的parkNanos方法，帶有時間。
5、無限期等待（Waiting）
執行中（Running）的執行緒執行了以下方法：
Object的wait方法，並且沒有使用timeout引數;
Thread的join方法，沒有使用timeout引數；
LockSupport的park方法；
Conditon的await方法。
6、阻塞（Blocked）
阻塞狀態是指執行緒因為某種原因放棄了cpu 使用權，暫時停止執行。直到執行緒進入可執行(runnable)狀態，才有機會再次獲得cpu timeslice 轉到執行(running)狀態。阻塞的情況分兩種：
同步阻塞：執行(running)的執行緒進入了一個synchronized方法，若該同步鎖被別的執行緒佔用，則JVM會把該執行緒放入鎖池(lock pool)中。
其他阻塞：執行(running)的執行緒發出了I/O請求時，JVM會把該執行緒置為阻塞狀態。當I/O處理完畢時，執行緒重新轉入可執行(runnable)狀態。
7、結束（Terminated）
執行緒run()、main() 方法執行結束，或者因異常退出了run()方法，則該執行緒結束生命週期。
執行緒狀態探祕
jstack檢視執行緒狀態
jstack -l <pid>
即可察看執行緒狀態，如何使用呢？
隨便寫一個死迴圈看一下
public class TestThreadState {
public static void main(String[] args) {
for (; ; ) {
}
}
}
ps -ef|grep TestThreadState
，找到對應的pid，jstack -l <pid>即可，如果未輸出執行緒資訊，可以嘗試使用-F引數來強制輸出。
"main" #1 prio=5 os_prio=31 tid=0x00007f8194801800 nid=0x1603 runnable [0x000070000a9b4000] java.lang.Thread.State: RUNNABLE at org.java.bin.TestThreadState.main(TestThreadState.java:12)