All
I have a question about pthread_cond_wait(). In short, I create two POSIX thread in a process, If I execute the following code, why is cpu utilization full?
I take experiments on it, if I remove comment mark before bool isNodeConnect3, the program seems to be no probelm, CPU utilization is almost 0%, in other words, theads will go to sleep and don't spend CPU resource, that's what I want.
Is it a data algnment probelm? maybe, but I don't think so, because I bracket my struct by "#pragma pack(push,1) ... #pragma (pop)" Could you give me suggestion??
Environment
Host OS is win7/intel 64 bit, guest OS is ubuntu 10.04LTS
Give "number of processor cores:4" to guest OS
The following is my test code, you can build and run it by
gcc -o program1 program1.c -pthread && ./program1
Get CPU utilization is 25%. Result depends on your setting.
Thanks a lot.
Code
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <fcntl.h>
#include <string.h>
#include <pthread.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <errno.h>
#include <stdbool.h>
#pragma pack(push,1)
struct BUFF_TX{
pthread_mutex_t mutex_lock;
pthread_cond_t more;
};
struct AtreeNode{
struct BUFF_TX buff_tx;
bool isNodeConnect;
bool isNodeConnect1;
bool isNodeConnect2;
// bool isNodeConnect3; // important
pthread_t thrd_tx;
};
struct AtreeNode treeNode[2];
int tmp[2];
#pragma (pop)
void Thread_TX(int *nodeIdx)
{
int idx = *nodeIdx;
while(1)
{
printf("Thread %d enter mutex lock...\n", idx);
pthread_mutex_lock(&treeNode[idx].buff_tx.mutex_lock);
while(1)
{
if(idx==0)
{
printf("idx==0 wait...\n");
pthread_cond_wait(&(treeNode[0].buff_tx.more), &treeNode[idx].buff_tx.mutex_lock);
}
else if(idx==1)
{
printf("idx==1 wait...\n");
pthread_cond_wait(&(treeNode[1].buff_tx.more), &treeNode[idx].buff_tx.mutex_lock);
}
else
printf("err\n");
}
pthread_mutex_unlock(&treeNode[idx].buff_tx.mutex_lock);
printf("Thread %d leave mutex lock...\n", idx);
}
}
int main(int argc, char *argv[])
{
int i;
int ret;
tmp[0] = 0;
tmp[1] = 1;
for(i=0; i<2; i++)
{
if(pthread_cond_init(&treeNode[i].buff_tx.more, NULL) != 0)
{
printf("cond %d init fail.\n", i);
exit(EXIT_FAILURE);
}
if(pthread_mutex_init(&treeNode[i].buff_tx.mutex_lock, NULL) != 0)
{
printf("mutex lock %d init fail.\n", i);
exit(EXIT_FAILURE);
}
}
for(i=0; i<2; i++)
{
ret = pthread_create(&treeNode[i].thrd_tx, NULL, (void *)Thread_TX, (void *)(&tmp[i]));
if(ret)
{
printf("pthread_create thrd_tx %d err\n", i);
return false;
}
}
pthread_join(treeNode[0].thrd_tx, NULL);
pthread_join(treeNode[1].thrd_tx, NULL);
exit(EXIT_SUCCESS);
}
