getting semaphores to work

[v3dant]

#include <iostream>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
using namespace std;

void *producer(void *ptr);
void handler(void *ptr);

sem_t mutex;
int counter=0;

int main()
{
	int i; int numThreads=1;
	pthread_t *myThreads;
	myThreads=new pthread_t [numThreads];
	sem_init(&mutex, 0, 1);
        srand((unsigned)time(NULL));
    	for(i=0; i<numThreads; i++)
    	{                                 
    		pthread_create(&myThreads[i],NULL,producer,(void *)i);
    	}
    	for(i=0; i<numThreads; i++)
    	{
        	pthread_join(myThreads[i],NULL);
    	}
    	sem_destroy(&mutex);
    	return(0);
}

void *producer(void *ptr)
{
	int x;
	int b;
	b = (rand() & 255);
	for(x=0; x<b; x++)
	{
		if( (rand() & 1) == 0)
		{
			handler(ptr);
		}
	}
	return 0;
}

void handler(void *ptr)
{
    	sem_wait(&mutex);
    	counter++;
    	cout<<"Thread "<<ptr<<" New Counter Value: "<<counter<<endl;
	sem_post(&mutex);
}

I am trying to compile the following code under NetBSD, using the g++ compiler. Get the following errors:
/var/tmp//ccpSzRS9.o(.text+0x39): In function `main':
: undefined reference to `sem_init'
/var/tmp//ccpSzRS9.o(.text+0xb1): In function `main':
: undefined reference to `pthread_join'
/var/tmp//ccpSzRS9.o(.text+0xc8): In function `main':
: undefined reference to `sem_destroy'
/var/tmp//ccpSzRS9.o(.text+0x135): In function `handler(void*)':
: undefined reference to `sem_wait'
/var/tmp//ccpSzRS9.o(.text+0x1a3): In function `handler(void*)':
: undefined reference to `sem_post'

Any ideas on how to fix these errors? I think it something with the libraries.

[Stack Overflow]

Hello,

From my past coding experience, I have not used semaphores in C++. Therefore I may not be able to help you as much as possible.

Though, here are some useful links on using Semaphore:

• Using Semaphores
• Using Semaphores in C++

I will continue my research on Semaphores to see if any more information arises.


- Stack Overflow

[PJYelton]

Which header file are those functions supposed to be in, and have you opened up the files themselves to see if in fact they are there?

[Codeplug]

Do you have "-lpthread -lrt" in your makefile to link with the pthread and realtime libraries?

gg

[v3dant]

that did the work, thanks

[azteched]

Incidentally, why use semaphores? A mutex would be more efficient.