簡介
POSIX thread 簡稱爲pthread，Posix線程是一個POSIX標準線程.該標準定義內部API創建和操縱線程.
作用
線程庫實行了POSIX線程標準通常稱爲pthreads.pthreads是最常用的POSIX系統如Linux和Unix,而微軟Windowsimplementations同時存在.舉例來說,pthreads-w32可支持MIDP的pthread
Pthreads定義了一套 C程序語言類型、函數與常量，它以 pthread.h 頭文件和一個線程庫實現。
數據類型
pthread_t：線程句柄
pthread_attr_t：線程屬性
線程操縱函數（簡介起見，省略參數）
pthread_create()：創建一個線程
pthread_exit()：終止當前線程
pthread_cancel()：中斷另外一個線程的運行
pthread_join()：阻塞當前的線程，直到另外一個線程運行結束
pthread_attr_init()：初始化線程的屬性
pthread_attr_setdetachstate()：設置脫離狀態的屬性（決定這個線程在終止時是否可以被結合）
pthread_attr_getdetachstate()：獲取脫離狀態的屬性
pthread_attr_destroy()：刪除線程的屬性
pthread_kill()：向線程發送一個信號
同步函數
用於 mutex 和條件變量
pthread_mutex_init() 初始化互斥鎖
pthread_mutex_destroy() 刪除互斥鎖
pthread_mutex_lock()：佔有互斥鎖（阻塞操作）
pthread_mutex_trylock()：試圖佔有互斥鎖（不阻塞操作）。當互斥鎖空閒時將佔有該鎖；否則立即返回
pthread_mutex_unlock(): 釋放互斥鎖
pthread_cond_init()：初始化條件變量
pthread_cond_destroy()：銷燬條件變量
pthread_cond_wait(): 等待條件變量的特殊條件發生
pthread_cond_signal(): 喚醒第一個調用pthread_cond_wait()而進入睡眠的線程
Thread-local storage（或者以Pthreads術語，稱作 線程特有數據）:
pthread_key_create(): 分配用於標識進程中線程特定數據的鍵
pthread_setspecific(): 爲指定線程特定數據鍵設置線程特定綁定
pthread_getspecific(): 獲取調用線程的鍵綁定，並將該綁定存儲在 value 指向的位置中
pthread_key_delete(): 銷燬現有線程特定數據鍵
與一起工作的工具函數
pthread_equal(): 對兩個線程的線程標識號進行比較
pthread_detach(): 分離線程
pthread_self(): 查詢線程自身線程標識號
詳細請參見：
Linux多線程pthread： http://blog.csdn.net/Sunboy_2050/archive/2010/10/04/5920936.aspx
Pthread多線程學習小結： http://blog.csdn.net/Sunboy_2050/archive/2010/10/04/5921003.aspx
===================================================================
多線程創建
參考代碼：
#include<stdio.h>
#include<pthread.h>
#include<string.h>
#include<sys/types.h>
#include<unistd.h>
pthread_t main_tid;
void print_ids(constchar *str)
{
pid_t pid; //進程id
pthread_t tid; //線程id
pid = getpid(); //獲取當前進程id
tid = pthread_self(); //獲取當前線程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); //創建線程
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;
}
運行結果：
[[email protected] pthread]$ gcc -Wall -o pthread_create pthread_create.c -lpthread
[[email protected] pthread]$ ./pthread_create
main thread: pid: 12531 tid: 2505487232 (0x9556b380)
main thread: pid: 12531 tid: 2505487232 (0x9556b380)
new thread: pid: 12531 tid: 1084229984 (0x40a00960)
===================================================================
多線程條件變量
參考代碼：
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
pthread_mutex_t counter_lock; //互斥鎖
pthread_cond_t counter_nonzero; //條件變量
int counter = 0;
int estatus = -1;
void *decrement_counter(void *argv);
void *increment_counter(void *argv);
//******* 主函數 *******//
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); //創建線程1
if(ret){
perror("del:/n");
return 1;
}
ret = pthread_create(&thd2, NULL, increment_counter, NULL); //創建線程2
if(ret){
perror("inc: /n");
return 1;
}
int counter = 0;
while(counter != 10){
printf("counter(main): %d/n", counter); //主線程
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); //進入阻塞(wait)，等待激活(signal)
printf("counter--(before): %d/n", counter);
counter--; //等待signal激活後再執行
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)的線程(先執行完signal線程，然後再執行wait線程)
printf("counter++(before): %d/n", counter);
counter++;
printf("counter++(after): %d/n", counter);
pthread_mutex_unlock(&counter_lock);
return &estatus;
}
運行結果：
[[email protected] pthread]$ gcc -Wall -o pthread_cond2 pthread_cond2.c -lpthread
[[email protected] 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
詳細解釋，請見：http://blog.csdn.net/Sunboy_2050/archive/2010/11/24/6031723.aspx
===================================================================
多線程的創建特殊數據鍵
參考代碼：
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
pthread_key_t key; //聲明參數key
void echomsg(void *arg) //析構處理函數
{
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); // 與key值綁定的value(tid)
printf("%s: thread %u returns %p/n", // %p 表示輸出指針格式
(char *)arg,
(unsigned int)tid,
pthread_getspecific(key)); // 獲取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;
}
//******* 主函數 *******//
int main(void)
{
pthread_t tid1, tid2;
printf("hello main/n");
pthread_key_create(&key, echomsg); //創建key
pthread_create(&tid1, NULL, child_1, (void *)"child_1"); //創建帶參數的線程，需要強制轉換
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;
}
運行結果：
[[email protected] pthread]$ gcc -Wall -o pthread_setspecific pthread_setspecific.c -lpthread
[[email protected] 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
附加參考——函數原型：
Posix定義了兩個API分別用來創建和註銷TSD：
void * pthread_getspecific(pthread_key_t key)
===================================================================
多線程的創建特殊數據鍵
參考代碼：
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
pthread_once_t once = PTHREAD_ONCE_INIT; //聲明變量
//once_run()函數僅執行一次，且究竟在哪個線程中執行是不定的
//儘管pthread_once(&once,once_run)出現在兩個線程中
//函數原型：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); //調用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); //調用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主線程等待線程tid1返回
pthread_join(tid2, NULL); //main主線程等待線程tid2返回
printf("bye main/n");
return 0;
}
運行結果：
[email protected] pthread]$ gcc -Wall -o pthread_once pthread_once.c -lpthread
[[email protected] pthread]$ ./pthread_once
hello main
Func: once_run in thread: 1084229984
child_1: thread 1084229984 returns
child_2: thread 1094719840 returns
bye main