pthread_xxx 的函数并没有直接提供设置一个pthread为守护线程的api
而pthread_attr_init（） 和 struct pthread_attr_t 也并没有提供 线程是否被设置为守护线程的成员变量
但java 的线程对象有 setDaemon() 方法将线程设置为守护线程
那我们看看java的Thread的native层是如何实现该变量的功能的
void Thread::CreateNativeThread(JNIEnv* env, jobject java_peer, size_t stack_size, bool is_daemon) {
。。。
623 Thread* child_thread = new Thread(is_daemon); // is_daemon 是关键
。。。
好像和native 的 pthread并没有什么关系。。。可能和jvm里有相关处理逻辑。
所以说 linux 下是不存在原生的pthread是否为守护进程概念的（最多只有守护进程概念）
linux下pthread行为：
- L1.子线程为守护线程（默认情况，linux下创建pthread 天生就是守护线程，行为和J2. java中调用setDaemon（true）后一致）：
- 1.mainThread跑完main函数，subThread立刻退出，mainThread退出，整个进程退出
- 2.subThread跑完，subThread退出，mainThread跑完main函数，mainThread退出，整个进程退出
java下thread行为：
- J1.子线程不为守护线程（默认情况，java下创建thread天生不是守护进程）：
- 1.mainThread跑完main函数，subThread立刻退出，mainThread退出，jvm退出，进程退出
- 2.subThread跑完，subThread退出，mainThread跑完main函数，mainThread退出，jvm退出，进程退出
- J2.子线程为守护线程（调用setDaemon（true），和linux下子线程创建后，行为和linux中默认创建pthread后一致）：
- 1.mainThread跑完main函数，subThread继续跑到退出，subThread退出，mainThread退出，jvm退出，进程退出
- 2.subThread跑完，subThread退出，mainThread跑完main函数，mainThread退出，jvm退出，进程退出
总结
1.守护线程行为
linux下默认创建线程 = java下创建后调用setDeamon（true）
行为：只要主线程执行完了，守护线程立刻销毁，进程退出
2.非守护线程行为
linux下无法直接将线程设置为非守护进程 = java下默认创建的线程默认就是非守护线程
行为：任何一个非守护线程执行完了，立刻销毁自己（无论主线程还是子线程），整个进程中非守护进程数量 > 0，进程不会退出；整个进程中非守护进程数量 == 0，立刻剩余销毁守护进程，并退出进程
L1代码：
L1.1.
#include<stdio.h>
#include<unistd.h>
#include<pthread.h>
void msleep(unsigned int s){
printf("tid: %d, start sleep %d\n",pthread_self(),s);
sleep(s);
printf("tid: %d, end sleep %d\n",pthread_self(),s);
}
int fun2(){
printf("fun2() start\n");
pthread_detach(pthread_self());
printf("current tid:%d\n",pthread_self());
msleep(5);
printf("fun2() end\n");
return 1;
}
void main(){
int res;
pthread_t pt2;
printf("main() start\n");
//pthread_attr_init();
res = pthread_create(&pt2,NULL,fun2,NULL);
//printf("res: %d\n",res);
msleep(3);
printf("main() end\n");
}
输出
[email protected]:~/cdir/dthreaddemo# ./dt1 main() start tid: -1624217856, start sleep 3 fun2() start current tid:-1632536832 tid: -1632536832, start sleep 5 tid: -1624217856, end sleep 3 main() end
可以看到并没有 fun2() end 输出
L2.2.
代码
#include<stdio.h>
#include<unistd.h>
#include<pthread.h>
void msleep(unsigned int s){
printf("tid: %d, start sleep %d\n",pthread_self(),s);
sleep(s);
printf("tid: %d, end sleep %d\n",pthread_self(),s);
}
int fun2(){
printf("fun2() start\n");
pthread_detach(pthread_self());
printf("current tid:%d\n",pthread_self());
msleep(3);
printf("fun2() end\n");
return 1;
}
void main(){
int res;
pthread_t pt2;
printf("main() start\n");
//pthread_attr_init();
res = pthread_create(&pt2,NULL,fun2,NULL);
//printf("res: %d\n",res);
msleep(5);
printf("main() end\n");
}
输出
[email protected]:~/cdir/dthreaddemo# ./dt1 main() start tid: -1453377792, start sleep 5 fun2() start current tid:-1461696768 tid: -1461696768, start sleep 3 tid: -1461696768, end sleep 3 fun2() end tid: -1453377792, end sleep 5 main() end
J1.1
代码
public class Test1 {
public static void main(String[] args) {
System.out.println("main start");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("t2 start");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2 end");
}
});
// t2.isDaemon(); //default is false
t2.setDaemon(false);
t2.start();
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2.isAlive() " + t2.isAlive());
System.out.println("main end");
}
}
输出
main start t2 start t2.isAlive() true main end t2 end Process finished with exit code 0
J1.2.
代码
public class Test1 {
public static void main(String[] args) {
System.out.println("main start");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("t2 start");
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2 end");
}
});
// t2.isDaemon(); //default is false
t2.setDaemon(false);
t2.start();
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2.isAlive() " + t2.isAlive());
System.out.println("main end");
}
}
输出
main start
t2 start
t2 end
t2.isAlive() false
main end
Process finished with exit code 0
J2.1.
代码
public class Test1 {
public static void main(String[] args) {
System.out.println("main start");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("t2 start");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2 end");
}
});
// t2.isDaemon(); //default is false
t2.setDaemon(true);
t2.start();
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2.isAlive() " + t2.isAlive());
System.out.println("main end");
}
}
输出
main start t2 start t2.isAlive() true main end Process finished with exit code 0
J2.2.
代码
public class Test1 {
public static void main(String[] args) {
System.out.println("main start");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
System.out.println("t2 start");
try {
Thread.sleep(3000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2 end");
}
});
// t2.isDaemon(); //default is false
t2.setDaemon(true);
t2.start();
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("t2.isAlive() " + t2.isAlive());
System.out.println("main end");
}
}
输出
main start t2 start t2 end t2.isAlive() false main end Process finished with exit code 0
这里不考虑线程调度的极端问题，如活锁之类的，或导致某个线程一致无法被分配到时间片等情况。
原文地址：https://www.cnblogs.com/cyy12/p/12216411.html
时间： 2024-11-29 10:56:48