一、多線程 VS 多進(jìn)程
和進(jìn)程相比，線程有很多優(yōu)勢。在Linux系統(tǒng)下，啟動(dòng)一個(gè)新的進(jìn)程必須分配給它獨(dú)立的地址空間，建立眾多的數(shù)據(jù)表來維護(hù)代碼段和數(shù)據(jù)。而運(yùn)行于一個(gè)進(jìn)程中的多個(gè)線程，他們之間使用相同的地址空間。正是這樣，同一進(jìn)程下的線程之間共享數(shù)據(jù)空間，數(shù)據(jù)可以相互使用，并且線程間切換也要更快些，可以更有效的利用CPU。
二、程序設(shè)計(jì)
[注] 頭文件pthread.h> 編譯時(shí)要加載動(dòng)態(tài)庫 libpthread.a，使用 -lpthread
1、創(chuàng)建線程
2、等待線程
3、關(guān)閉線程
4、退出清除
1、創(chuàng)建線程
int pthread_create(pthread_t *tidp, const pthread_attr_t *attr, void *(*start_rtn)(void), void *arg)
tidp為線程id，是函數(shù)分配的值，所以要傳一個(gè) pthread_t 的地址。
attr線程屬性，通常為空。
start_rtn為線程要執(zhí)行的函數(shù)，返回值為空指針，參數(shù)為后面的*arg
若成功則返回0，否則返回出錯(cuò)編號。
例：
#includestdio.h>
#includepthread.h>/p>
p>void *func1(void *arg){ //原函數(shù)聲明
int i;
for(i=0;i5;i++){
printf("this is func1! The num is %d\n",*(int*)arg); //將空指針轉(zhuǎn)換為int型指針
sleep(1);
}
}/p>
p>void *func2(int *m){ //自定義類型聲明，也可以定義非指針類型，但是在create時(shí)會有警告，因?yàn)榉堑刂凡⒉荒芨淖儌魅氲闹?br /> int i;
for(i=0;i5;i++){
printf("this is func2! The num is %d\n",*m);
(*m)++;
sleep(1);
}
}/p>
p>int main(){
pthread_t id1,id2;
int num = 5;
int *p = num;
if(pthread_create(id1,NULL,(void *)func1,(void *)p) != 0){
printf("thread1 create error!\n");
return -1;
}
if(pthread_create(id2,NULL,(void *)func2,num) != 0){
printf("thread2 create error!\n");
return -1;
}
pthread_join(id1,NULL); //等待線程結(jié)束
pthread_join(id2,NULL);
printf("Running complete!\n");
return 0;/p>
p>
}
運(yùn)行結(jié)果：
[fsy@localhost process]$ gcc thC.c -o thC -lpthread -g
[fsy@localhost process]$ ./thC
this is func2! The num is 5
this is func1! The num is 6
this is func2! The num is 6
this is func1! The num is 7
this is func2! The num is 7
this is func1! The num is 8
this is func2! The num is 8
this is func1! The num is 9
this is func2! The num is 9
this is func1! The num is 10
Running complete!
[fsy@localhost process]$
2、等待線程
[注]當(dāng)調(diào)用pthread_create函數(shù)時(shí)，線程并沒有開始執(zhí)行，主進(jìn)程應(yīng)有等待，比如用sleep，或者用更專業(yè)的函數(shù)：pthread_join
int pthread_join(pthread_t tid, void **rval_ptr)
調(diào)用函數(shù)可以阻塞調(diào)用線程，直到指定的線程終止。
tid為等待退出線程的id，rval_ptr為函數(shù)的返回值。是指向指針的指針，可以置空。
例：
#includestdio.h>
#includepthread.h>
#includestdlib.h>/p>
p>void *func(int *p){
int *num=(int *)malloc(sizeof(int)); //必須動(dòng)態(tài)創(chuàng)建，原因可以參考我動(dòng)態(tài)分配內(nèi)存的博客
printf("Please input the number: ");
scanf("%d",num);
return (void *)num; //類型是pthread_create的參數(shù)規(guī)定的
}/p>
p>int main(){
pthread_t pth;
void *a;
if(pthread_create(pth,NULL,(void *)func,NULL) != 0){
printf("create thread error!\n");
return 1;
}
pthread_join(pth,a); //指向空指針的指針
printf("get the num from the thread, it's %d\n",*(int *)a);
return 0;
}
3、終止線程
線程終止有以下三種方式：
1、線程從函數(shù)中返回
2、線程可以別其他函數(shù)終止
3、線程自己調(diào)用pthread_exit函數(shù)
void pthread_exit(void *rval_ptr)
rval_ptr為線程退出返回值的指針，即函數(shù)返回值。
4、退出清除
void pthread_cleanup_push(void (*rtn)(void*), void *arg)
rtn為清除函數(shù)，arg是清除函數(shù)的參數(shù)
void pthread_cleanup_pop(int execute)
當(dāng)execute 非0時(shí)執(zhí)行清除函數(shù)。為0時(shí)不執(zhí)行。
從pthread_cleanup_push的調(diào)用點(diǎn)到pthread_cleanup_pop之間的程序段中，如果有終止進(jìn)程的動(dòng)作，如調(diào)用pthread_exit或異常終止（不包括return），就會執(zhí)行pthread_cleanup_push()所指定的清理函數(shù)。多個(gè)嵌套匹配時(shí)，就近匹配。
例：
#includestdio.h>
#includepthread.h>/p>
p>void *clean(char *argv){
printf("clean is called by %s\n",argv);
return NULL;
}
void *func1(void *argv){
printf("welcome enter the func1!\n");
pthread_cleanup_push((void*)clean,"the first time call!");
pthread_cleanup_push((void*)clean,"the second time call!");
if(argv){
return (void *)1; //第二次運(yùn)行將此句注掉
}
pthread_cleanup_pop(0);
pthread_cleanup_pop(1);
return (void *)0;
}/p>
p>void *func2(void *argv){
sleep(1); //兩個(gè)線程運(yùn)行先后不確定
printf("welcome enter the func2!\n");
pthread_cleanup_push((void*)clean,"the first time call!");
pthread_cleanup_push((void*)clean,"the second time call!");
if(argv){
pthread_exit(NULL);
}
pthread_cleanup_pop(0);
pthread_cleanup_pop(0);
return (void *)0;
}/p>
p>
int main(){
pthread_t tid1,tid2;
if(pthread_create(tid1,NULL,(void *)func1,(void *)1) != 0){
printf("thread1 create error!\n");
return 1;
}/p>
p> if(pthread_create(tid2,NULL,(void *)func2,(void *)1) != 0){
printf("thread2 create error!\n");
return 1;
}
pthread_join(tid1,NULL);
pthread_join(tid2,NULL);
return 0;
}
運(yùn)行結(jié)果：
[fsy@localhost process]$ gcc thClean.c -o thclean -lpthread
[fsy@localhost process]$ ./thclean
welcome enter the func1!
welcome enter the func2!
clean is called by the second time call! //此處先2后1
clean is called by the first time call!
[fsy@localhost process]$ vim thClean.c
[fsy@localhost process]$ gcc thClean.c -o thclean -lpthread
[fsy@localhost process]$ ./thclean
welcome enter the func1!
clean is called by the first time call! //second已經(jīng)被pop
welcome enter the func2!
clean is called by the second time call!
clean is called by the first time call!
[fsy@localhost process]$
