附上代码，仅供参考，三个线程的同步..


#include<iostream>
using namespace std;
#include <pthread.h>
#include <semaphore.h>
#include <pthread.h>
#include <unistd.h>
int buff;//

bool first=false;
pthread_cond_t read_cond=PTHREAD_COND_INITIALIZER;
pthread_cond_t write1_cond=PTHREAD_COND_INITIALIZER;
pthread_cond_t write2_cond=PTHREAD_COND_INITIALIZER;
pthread_mutex_t mutex=PTHREAD_MUTEX_INITIALIZER;

void *Read(void *arg)
{

int i=1;
while(1)
{
cout<<"in read ... "<<endl;
pthread_cond_wait(&read_cond,&mutex);
buff=i;
if(i%2==0)
{
pthread_cond_signal(&write2_cond);
}
else
{
pthread_cond_signal(&write1_cond);
}
i++;
}

return NULL;
}

void *Write1(void *arg)
{
cout<<" in write1"<<endl;
while(1)
{
pthread_cond_wait(&write1_cond,&mutex);
if(!first)
{
first=true;
}
cout<<buff<<"  write one---"<<endl;
buff=-1;
pthread_cond_signal(&read_cond);
}

return NULL;
}
void *Write2(void *arg)
{
cout<<"in write2"<<endl;
while(1)
{
pthread_cond_wait(&write2_cond,&mutex);
cout<<buff<<"   write two---"<<endl;
buff=-1;
pthread_cond_signal(&read_cond);
}

return NULL;
}

int main()
{
pthread_t pid1,pid2,pid3;

pthread_create(&pid1,NULL,Read,NULL);
pthread_create(&pid2,NULL,Write1,NULL);
pthread_create(&pid3,NULL,Write2,NULL);

while(first == false )
{
pthread_cond_signal(&read_cond);
usleep(10);
}

while(1)
{

usleep(2000);
}

pthread_join(pid1,NULL);
pthread_join(pid2,NULL);
pthread_join(pid3,NULL);

pthread_cond_destroy(&read_cond);
pthread_cond_destroy(&write1_cond);
pthread_cond_destroy(&write2_cond);
return 0;
}