Linux多线程Pthread学习小结

简介

POSIX thread 简称为pthread，Posix线程是一个​​POSIX​​标准线程.该标准定义内部API创建和操纵线程.

作用

线程库实行了POSIX线程标准通常称为pthreads.pthreads是最常用的POSIX系统如Linux和Unix,而微软Windowsimplementations同时存在.举例来说,pthreads-w32可支持MIDP的pthread

Pthreads定义了一套 C程序语言类型、函数与常量，它以 pthread.h 头文件和一个线程库实现。

数据类型

pthread_t：线程句柄

pthread_attr_t：线程属性

线程操纵函数（简介起见，省略参数）

pthread_create()：创建一个线程

pthread_exit()：终止当前线程

pthread_cancel()：中断另外一个线程的运行

pthread_join()：阻塞当前的线程，直到另外一个线程运行结束

pthread_attr_init()：初始化线程的属性

pthread_attr_setdetachstate()：设置脱离状态的属性（决定这个线程在终止时是否可以被结合）

pthread_attr_getdetachstate()：获取脱离状态的属性

pthread_attr_destroy()：删除线程的属性

pthread_kill()：向线程发送一个信号

同步函数

用于 mutex 和条件变量

pthread_mutex_init() 初始化互斥锁

pthread_mutex_destroy() 删除互斥锁

pthread_mutex_lock()：占有互斥锁（阻塞操作）

pthread_mutex_trylock()：试图占有互斥锁（不阻塞操作）。当互斥锁空闲时将占有该锁；否则立即返回

pthread_mutex_unlock(): 释放互斥锁

pthread_cond_init()：初始化条件变量

pthread_cond_destroy()：销毁条件变量

pthread_cond_wait(): 等待条件变量的特殊条件发生

pthread_cond_signal(): 唤醒第一个调用pthread_cond_wait()而进入睡眠的线程

Thread-local storage（或者以Pthreads术语，称作 线程特有数据）:

pthread_key_create(): 分配用于标识进程中线程特定数据的键

pthread_setspecific(): 为指定线程特定数据键设置线程特定绑定

pthread_getspecific(): 获取调用线程的键绑定，并将该绑定存储在 value 指向的位置中

pthread_key_delete(): 销毁现有线程特定数据键

与一起工作的工具函数

pthread_equal(): 对两个线程的线程标识号进行比较

pthread_detach(): 分离线程

pthread_self(): 查询线程自身线程标识号

多线程创建

参考代码：

#include<stdio.h> #include<pthread.h> #include<string.h> #include<sys/types.h> #include<unistd.h> pthread_t main_tid; void print_ids(const char *str) { pid_t pid; //进程id pthread_t tid; //线程id pid = getpid(); //获取当前进程id tid = pthread_self(); //获取当前线程id printf("%s pid: %u tid: %u (0x%x)/n", str, (unsigned int)pid, (unsigned int)tid, (unsigned int)tid); } void *func(void *arg) { print_ids("new thread:"); return ((void *)0); } int main() { int err; err = pthread_create(&main_tid, NULL, func, NULL); //创建线程 if(err != 0){ printf("create thread error: %s/n",strerror(err)); return 1; } printf("main thread: pid: %u tid: %u (0x%x)/n", (unsigned int)getpid(), (unsigned int)pthread_self(), (unsigned int)pthread_self()); print_ids("main thread:"); sleep(1); return 0; }

运行结果：

[[e-mail] pthread]$ gcc -Wall -o pthread_create pthread_create.c -lpthread

[[e-mail] pthread]$ ./pthread_create

main thread: pid: 12531 tid: 2505487232 (0x9556b380)

main thread: pid: 12531 tid: 2505487232 (0x9556b380)

new thread: pid: 12531 tid: 1084229984 (0x40a00960)

===================================================================

多线程条件变量

参考代码：

#include <stdio.h> #include <pthread.h> #include <unistd.h> pthread_mutex_t counter_lock; //互斥锁 pthread_cond_t counter_nonzero; //条件变量 int counter = 0; int estatus = -1; void *decrement_counter(void *argv); void *increment_counter(void *argv); //******* 主函数 *******// int main(int argc, char **argv) { printf("counter: %d/n", counter); pthread_t thd1, thd2; int ret; //初始化 pthread_mutex_init(&counter_lock, NULL); pthread_cond_init(&counter_nonzero, NULL); ret = pthread_create(&thd1, NULL, decrement_counter, NULL); //创建线程1 if(ret){ perror("del:/n"); return 1; } ret = pthread_create(&thd2, NULL, increment_counter, NULL); //创建线程2 if(ret){ perror("inc: /n"); return 1; } int counter = 0; while(counter != 10){ printf("counter(main): %d/n", counter); //主线程 sleep(1); counter++; } pthread_exit(0); return 0; } void *decrement_counter(void *argv) { printf("counter(decrement): %d/n", counter); pthread_mutex_lock(&counter_lock); while(counter == 0) pthread_cond_wait(&counter_nonzero, &counter_lock); //进入阻塞(wait)，等待激活(signal) printf("counter--(before): %d/n", counter); counter--; //等待signal激活后再执行 printf("counter--(after): %d/n", counter); pthread_mutex_unlock(&counter_lock); return &estatus; } void *increment_counter(void *argv) { printf("counter(increment): %d/n", counter); pthread_mutex_lock(&counter_lock); if(counter == 0) pthread_cond_signal(&counter_nonzero); //激活(signal)阻塞(wait)的线程(先执行完signal线程，然后再执行wait线程) printf("counter++(before): %d/n", counter); counter++; printf("counter++(after): %d/n", counter); pthread_mutex_unlock(&counter_lock); return &estatus; }

运行结果：

[[e-mail] pthread]$ gcc -Wall -o pthread_cond2 pthread_cond2.c -lpthread

[[e-mail] pthread]$ ./pthread_cond2

counter: 0

counter(main): 0

counter(decrement): 0

counter(increment): 0

counter++(before): 0

counter++(after): 1

counter--(before): 1

counter--(after): 0

counter(main): 1

counter(main): 2

counter(main): 3

counter(main): 4

counter(main): 5

counter(main): 6

counter(main): 7

counter(main): 8

counter(main): 9

多线程的创建特殊数据键

参考代码：

#include <stdio.h> #include <pthread.h> #include <unistd.h> pthread_key_t key; //声明参数key void echomsg(void *arg) //析构处理函数 { printf("destruct executed in thread = %u, arg = %p/n", (unsigned int)pthread_self(), arg); } void *child_1(void *arg) { pthread_t tid; tid = pthread_self(); printf("%s: thread %u enter/n", (char *)arg, (unsigned int)tid); pthread_setspecific(key, (void *)tid); // 与key值绑定的value(tid) printf("%s: thread %u returns %p/n", // %p 表示输出指针格式 (char *)arg, (unsigned int)tid, pthread_getspecific(key)); // 获取key值的value sleep(1); return NULL; } void *child_2(void *arg) { pthread_t tid; tid = pthread_self(); printf("%s: thread %u enter/n", (char *)arg, (unsigned int)tid); pthread_setspecific(key, (void *)tid); printf("%s: thread %u returns %p/n", (char *)arg, (unsigned int)tid, pthread_getspecific(key)); sleep(1); return NULL; } //******* 主函数 *******// int main(void) { pthread_t tid1, tid2; printf("hello main/n"); pthread_key_create(&key, echomsg); //创建key pthread_create(&tid1, NULL, child_1, (void *)"child_1"); //创建带参数的线程，需要强制转换 pthread_create(&tid2, NULL, child_2, (void *)"child_2"); sleep(3); pthread_key_delete(key); //清除key printf("bye main/n"); pthread_exit(0); return 0; }

运行结果：

[[e-mail] pthread]$ gcc -Wall -o pthread_setspecific pthread_setspecific.c -lpthread

[[e-mail] pthread]$ ./pthread_setspecific                                          

hello main

child_1: thread 1084229984 enter

child_1: thread 1084229984 returns 0x40a00960

child_2: thread 1094719840 enter

child_2: thread 1094719840 returns 0x41401960

destruct executed in thread = 1084229984, arg = 0x40a00960

destruct executed in thread = 1094719840, arg = 0x41401960

bye main

附加参考——函数原型：

Posix定义了两个API分别用来创建和注销TSD：

int pthread_key_create(pthread_key_t *key, void (*destr_function) (void *)) 注销一个TSD采用如下API： int pthread_key_delete(pthread_key_t key) int pthread_setspecific(pthread_key_t key, const void *pointer)

void * pthread_getspecific(pthread_key_t key)

多线程的创建特殊数据键

参考代码：

#include <stdio.h> #include <pthread.h> #include <unistd.h> pthread_once_t once = PTHREAD_ONCE_INIT; //声明变量 //once_run()函数仅执行一次，且究竟在哪个线程中执行是不定的 //尽管pthread_once(&once,once_run)出现在两个线程中 //函数原型：int pthread_once(pthread_once_t *once_control, void (*init_routine)(void)) void once_run(void) { printf("Func: %s in thread: %u/n", __func__, (unsigned int)pthread_self()); } void *child_1(void *arg) { pthread_t tid; tid = pthread_self(); pthread_once(&once, once_run); //调用once_run printf("%s: thread %d returns/n", (char *)arg, (unsigned int)tid); return NULL; } void *child_2(void *arg) { pthread_t tid; tid = pthread_self(); pthread_once(&once, once_run); //调用once_run printf("%s: thread %d returns/n", (char *)arg, (unsigned int)tid); return NULL; } //******* main *******// int main(void) { pthread_t tid1, tid2; printf("hello main/n"); pthread_create(&tid1, NULL, child_1, (void *)"child_1"); pthread_create(&tid2, NULL, child_2, (void *)"child_2"); pthread_join(tid1, NULL); //main主线程等待线程tid1返回 pthread_join(tid2, NULL); //main主线程等待线程tid2返回 printf("bye main/n"); return 0; }

运行结果：

​​[e-mail]​​ pthread]$ gcc -Wall -o pthread_once pthread_once.c -lpthread

[[e-mail] pthread]$ ./pthread_once                                   

hello main

Func: once_run in thread: 1084229984

child_1: thread 1084229984 returns

child_2: thread 1094719840 returns

bye main