JUC概述1：
首先是進程和線程的概念：
進程：是指系統在系統中正在運行的一個應用程序，程序一旦運行就是進程，進程是資源分配的最小單位
線程：進程之內獨立執行，是程序執行的最小單位
線程的六大狀態：在線程的枚舉類中
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 {@code Object.wait()}
* on an object is waiting for another thread to call
* {@code Object.notify()} or {@code Object.notifyAll()} on
* that object. A thread that has called {@code Thread.join()}
* 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;
}
| 狀態名稱 | 說明 |
|---|---|
| new | 初始狀態 |
| runnable | 運行狀態 |
| blocked | 阻塞狀態 |
| waiting | 等待狀態，一直等(不見不散) |
| time_waiting | 超時等待，（過時不候） |
| terminated | 終止狀態 |
wait和sleep的區別：
- sleep是Thread的靜態方法，wait是Object的方法，任何對象實例化都能調用
- sleep不會釋放鎖，他也不需要佔用鎖，wait會釋放鎖，但是調用它的前提是當前線程佔有鎖
- 它們都可以interrupted被中斷
併發和並行：
併發是指多個事情在同一個時間段中執行
並行是指多個事情在同一時刻執行
管程：
是一種同步機制，保證同一時間內只有一個線程訪問被保護數據或者代碼
jvm同步基於進入(加鎖)和退出(解鎖)，是管程對象實現的
大意就是進加鎖，退是解鎖，通過管程對象管理
用戶線程：自定義線程 主線程結束了，用戶線程還存在，則表示JVM還存在
public class demo {
public static void main(String[] args) {
Thread a = new Thread(() -> {
System.out.println(Thread.currentThread().getName()+"::"+Thread.currentThread().isDaemon());
while (true){}
}, "a");
a.start();
System.out.println(Thread.currentThread().getName());
}
}
守護線程：
ex:垃圾回收 沒有用戶線程了，都是守護線程，JVM結束
public class demo {
public static void main(String[] args) {
Thread a = new Thread(() -> {
System.out.println(Thread.currentThread().getName()+"::"+Thread.currentThread().isDaemon());
while (true){}
}, "a");
//設置子線程爲守護線程
a.setDaemon(true);
a.start();
System.out.println(Thread.currentThread().getName());
}
}
