1 What are Threads?

一个进程可以有多个线程
线程共享进程的资源,多进程是复制内存空间,彼此独立
线程被OS调度,意味着一个进程会使用超过100%的cpu(多核系统)

2 Hello POSIX Threads?

POSIX became the standard interface for many system(C,Java,Python)

2.1 Creating a Thread

/* hello_pthread.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <pthread.h>void * hello_fun(void * args){printf("Hello World!\n");return NULL;
}int main(int argc, char * argv[]){pthread_t thread;  //thread identifier//create a new thread have it run the function hello_funpthread_create(&thread, NULL, hello_fun, NULL);//wait until the thread completespthread_join(thread, NULL);return 0;
}

pthread_create()创建线程,运行hello_fun,并用thread指针接收
pthread_join()主线程阻塞,直到thread执行结束
int pthread_create(pthread_t *thread, const pthread_attr_t *attr,void *(*start_routine) (void *), void *arg);

2.2 Passing Arguments to a Thread

/* hello_args_pthread.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <pthread.h>void * hello_arg(void * args){char * str = (char *) args;printf("%s", str);return NULL;
}int main(int argc, char * argv[]){char hello[] = "Hello World!\n";pthread_t thread;  //thread identifier//create a new thread that runs hello_arg with argument hellopthread_create(&thread, NULL, hello_arg, hello);//wait until the thread completespthread_join(thread, NULL);return 0;
}

2.3 Joining Threads

thread的join很像process的wait
线程之间可以相互join
3.当主线程退出时,其他所有线程自动销毁,所以不会产生僵尸和浪费资源

/* hello_pthread_bad.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <pthread.h>void * hello_fun(){printf("Hello World!\n");return NULL;
}int main(int argc, char * argv[]){pthread_t thread;pthread_create(&thread, NULL, hello_fun, NULL);return 0;
}

2.4 Return values from threads

1.int pthread_join(pthread_t thread, void **retval);
2.类似于进程中的exit函数传递进程退出的状态,线程可以返回任何参数

2.5 Compiling POSIX threads

3 Threads and the OS

系统层面,pid和tid是相同的,既主线程和进程的id是相同的
线程内部tid和pid是不同的

/* hello_id_pthread.c*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <unistd.h>
#include <sys/types.h>
#include <sys/syscall.h>#include <pthread.h>//have to call syscall directly, no libc wrapper
pid_t gettid(){return (pid_t) syscall (SYS_gettid);
}void * hello_fun(void * args){//retrieve the thread_idpthread_t thread = pthread_self();//print all identifying informationprintf("THREAD: TID:%d PID:%d PthreadID:%lu\n", gettid(), getpid(), thread);return NULL;
}int main(int argc, char * argv[]){pthread_t thread;  //thread identifier//create a new thread have it run the function hello_funpthread_create(&thread, NULL, hello_fun, NULL);//print all identifying informationprintf("MAIN: TID:%d PID:%d \n", gettid(), getpid());//wait until the thread completespthread_join(thread, NULL);return 0;
}

3.2 Threads Running Like Processes

C中每个线程可以占用一个cpu核

参考:
https://www.usna.edu/Users/cs/aviv/classes/ic221/s16/lec/28/lec.html#coderef-bad_ref

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28 POSIX Threads

1 What are Threads?

2 Hello POSIX Threads?

2.1 Creating a Thread

2.2 Passing Arguments to a Thread

2.3 Joining Threads

2.4 Return values from threads

2.5 Compiling POSIX threads

3 Threads and the OS

3.2 Threads Running Like Processes

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