linux下，两个线程依次执行

如何实现Linux下双线程的依次执行？

法1：设置一个flag变量， 线程1执行后，设置flag为2；线程2执行后，设置flag为1；代码如下：

#include <stdio.h>

#include <sys/types.h>

#include <sys/syscall.h>

#include <pthread.h>

#include <unistd.h>

#include <signal.h>

#include <stdbool.h>

int num = 0;

int flag = 1;

void function1()

{

while(num < 10000)

{

if(flag == 1)

{

num ++;

//printf("thread %d, num = %d\n",syscall(SYS_gettid),num);

flag = 2;

}

}

}

void function2()

{

while(num < 10000)

{

if(flag == 2)

{

num ++;

//printf("thread %d,num = %d\n",syscall(SYS_gettid),num);

flag = 1;

}

}

}

void main()

{

int ret1, ret2;

struct timeval start ,end;

float use;

gettimeofday(&start,NULL);

printf("getpid() = %d\n\n",getpid());

pthread_t p1,p2;

if(ret1 != 0)

{

printf("thread 1 create failed ..\n");

return;

}

ret2 = pthread_create(&p2, NULL, (void *)&function2, NULL);

if(ret2 != 0)

{

printf("thread 2 create failed ..\n");

return;

}

pthread_join(p1, NULL);

pthread_join(p2, NULL);

//pthread_mutex_destroy(&t1);

//pthread_cond_destroy(&cond1);

gettimeofday(&end, NULL);

use = 1000000*(start.tv_sec - end.tv_sec) + start.tv_usec - end.tv_usec ;

use = -use /1000000;

printf("all has done... %f s time elapsed..\n", use);

return;

}

上述代码完全可以胜任，问题在于打印10000次耗费时间20多秒。

肯定存在更好的办法：如下，借用线程互斥量和条件等待：

#include <stdio.h>

#include <sys/types.h>

#include <sys/syscall.h>

#include <pthread.h>

#include <unistd.h>

#include <signal.h>

#include <stdbool.h>

int num = 0;

bool des = true;

pthread_mutex_t t1 = PTHREAD_MUTEX_INITIALIZER;

pthread_cond_t cond1 = PTHREAD_COND_INITIALIZER;

int flag = 1;

void function1()

{

num ++ ;

pthread_cond_broadcast(&cond1);

while(num < 10000000)

{

pthread_mutex_lock(&t1);

while(flag == 1)

pthread_cond_wait(&cond1, &t1);

num ++ ;

printf("1 : num = %d\n",num);

pthread_mutex_unlock(&t1);

flag = 1;

pthread_cond_broadcast(&cond1);

}

}

void function2()

{

while(num < 10000000)

{

pthread_mutex_lock(&t1);

while(flag ==2)

pthread_cond_wait(&cond1, &t1);

num ++;

printf("2 : num = %d\n",num);

pthread_mutex_unlock(&t1);

flag = 2;

pthread_cond_broadcast(&cond1);

}

}

void main()

{

int ret1, ret2;

struct timeval start ,end;

float use;

gettimeofday(&start,NULL);

printf("getpid() = %d\n\n",getpid());

pthread_t p1,p2;

pthread_mutex_init(&t1, NULL);

pthread_cond_init(cond1, NULL);

ret1 = pthread_create(&p1, NULL, (void *)&function1, NULL);

if(ret1 != 0)

{

printf("thread 1 create failed ..\n");

return;

}

ret2 = pthread_create(&p2, NULL, (void *)&function2, NULL);

if(ret2 != 0)

{

printf("thread 2 create failed ..\n");

return;

}

pthread_join(p1, NULL);

pthread_join(p2, NULL);

pthread_mutex_destroy(&t1);

pthread_cond_destroy(&cond1);

gettimeofday(&end, NULL);

use = 1000000*(start.tv_sec - end.tv_sec) + start.tv_usec - end.tv_usec ;

use = -use /1000000;

printf("all has done... %f s time elapsed..\n", use);

return;

}

效率提升至少3个数量级。