嗨，我正在编写一个将字符串写入文件的程序，进程1将在文件中写入一个小写字母，进程2在同一文件中写入一个大写字母。我使用线程实现了一个程序，必须首先运行进程1，然后再运行进程2。程序如下。
/******************
* Header Files
******************/
#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
pthread_mutex_t lock;
void* write_p1()
{
if((pthread_mutex_lock(&lock)) != 0)
{
printf("pthread_mutex_lock() failed\n");
exit(1);
}
int index=0; /*used in for loop*/
int flag=0; /*flag used in capital letter and space detecion*/
FILE *fp=NULL; /*file pointer used to store open file*/
char str[100]; /*to store user string*/
printf("*****Hi, I am Process 1*****\n");
/*open the sample.txt file for write*/
fp=fopen("sample.txt","w");
if(fp==NULL)
{
printf("Not able to open file\n");
exit(1);
}
printf("Enter small letters\n");
fgets(str,100,stdin);
/*capital letter and space detection*/
if((strlen(str)>0)&&(str[strlen(str)-1]=='\n'))
{
str[strlen(str)-1]='\0';
}
for(index=0;str[index]!='\0';index++)
{
if(islower(str[index]) || str[index] == ' ')
{
flag=0;
}
else
{
printf("Enter Small Letters\n");
exit(1);
}
}
if(flag==0)
{
fprintf(fp,"%s",str);
}
/*close the file*/
fclose(fp);
printf("Entered string: %s\n",str);
if((pthread_mutex_unlock(&lock)) != 0)
{
printf("pthread_mutex_unlock() failed\n");
exit(1);
}
printf("\n\n");
}
void* write_p2()
{
if((pthread_mutex_lock(&lock)) != 0)
{
printf("pthread_mutex_lock() failed\n");
exit(1);
}
int index=0; /*used in for loop*/
int flag=0; /*flag used in small letter and space detecion*/
FILE *fp=NULL; /*file pointer used to store open file*/
char str[100]; /*to store user string*/
printf("*****Hi, I am Process 2*****\n");
/*open the sample.txt file for write*/
fp=fopen("sample.txt","a");
if(fp==NULL)
{
printf("Not able to open file\n");
exit(1);
}
printf("Enter Capital letters\n");
fgets(str,100,stdin);
/*capital letter and space detection*/
if((strlen(str)>0)&&(str[strlen(str)-1]=='\n'))
{
str[strlen(str)-1]='\0';
}
for(index=0;str[index]!='\0';index++)
{
if(isupper(str[index]) || str[index] == ' ')
{
flag=0;
}
else
{
printf("Enter capital Letters\n");
exit(1);
}
}
if(flag==0)
{
fprintf(fp,"%s",str);
}
/*close the file*/
fclose(fp);
printf("Entered string: %s\n",str);
if((pthread_mutex_unlock(&lock)) != 0)
{
printf("pthread_mutex_unlock() failed\n");
exit(1);
}
printf("\n\n");
}
int main(void)
{
/*initialized semaphore*/
if((pthread_mutex_init(&lock,NULL)) != 0)
{
printf("pthread_mutex_init() failed\n");
exit(1);
}
/*create a two thread*/
pthread_t t1=0,t2=0;
pthread_create(&t1,NULL,write_p1,NULL);
pthread_create(&t2,NULL,write_p2,NULL);
/*this function wait for thread to terminate*/
pthread_join(t1,NULL);
pthread_join(t2,NULL);
/*destroy the semaphore*/
if((pthread_mutex_destroy(&lock)) != 0)
{
printf("pthread_mutex_destroy() failed\n");
exit(1);
}
return 0;
}
现在，该程序正在运行，但是有时它将运行第一个线程2（进程2）或某个时间运行线程1（进程1），对此我需要一个解决方案，它必须在该线程2（进程1）之后首先运行线程1（进程1）。 2），那么我该怎么做？
最佳答案
我正在为您准备以下节目。您可以通过使用条件变量来实现。在您的代码中实现相同的过程。如何运作？为了开始控制过程，我们首先允许线程1。在主线程中（即主函数；每个程序都有一个主线程，在C / C ++中，一旦控件通过内核传递给主方法/函数，操作系统就会自动创建该主线程），我们正在调用pthread_cond_signal（＆cond1 ）;。从主线程调用此函数后，正在等待cond1的thread1将被释放，它将开始进一步执行。一旦完成其最终任务，它将调用pthread_cond_signal（＆cond2）;。现在，正在等待条件cond2的线程，即thread2，将被释放，它将开始执行其最后阶段
#include<pthread.h>
pthread_cond_t cond1 = PTHREAD_COND_INITIALIZER;
pthread_cond_t cond2 = PTHREAD_COND_INITIALIZER;
pthread_mutex_t lock1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t lock2 = PTHREAD_MUTEX_INITIALIZER;
int TRUE = 1;
void * threadMethod1(void *arg)
{
printf("In thread1\n");
do{
pthread_mutex_lock(&lock1);
//Add your business logic(parallel execution codes) here
pthread_cond_wait(&cond1, &lock1);
printf("I am thread1 generating the final report and inserting into file \n");
pthread_cond_signal(&cond2);/* Now allow 2nd thread to process */
pthread_mutex_unlock(&lock1);
}while(TRUE);
pthread_exit(NULL);
}
void * threadMethod2(void *arg)
{
printf("In thread2\n");
do
{
pthread_mutex_lock(&lock2);
//Add your business logic(parallel execution codes) here
pthread_cond_wait(&cond2, &lock2);
printf("I am thread2 generating the final report and inserting into a file \n");
pthread_cond_signal(&cond1);
pthread_mutex_unlock(&lock2);
}while(TRUE);
pthread_exit(NULL);
}
int main(void)
{
pthread_t tid1, tid2;
int i = 0;
printf("Before creating the threads\n");
if( pthread_create(&tid1, NULL, threadMethod1, NULL) != 0 )
printf("Failed to create thread1\n");
if( pthread_create(&tid2, NULL, threadMethod2, NULL) != 0 )
printf("Failed to create thread2\n");
pthread_cond_signal(&cond1);/* Now allow first thread to process first */
sleep(1);
TRUE = 0;/* Stop all the thread */
//sleep(3);
pthread_join(tid1,NULL);
pthread_join(tid2,NULL);
exit(0);
}