C++ pthread deadlock solution - c++

Question

I am trying to use p_thread to print out numbers in order like:
0
1
2
3
4
Without using a global variable, just local variable, but I met deadlock and I don't know how to fix it yet.
This is my code:
#include <pthread.h>
#include <iostream>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
static pthread_mutex_t bsem; // Mutex semaphore
static pthread_cond_t waitTurn = PTHREAD_COND_INITIALIZER; // Condition variable to control the turn
//static int turn; // Index to control access to the turn array
static int nthreads; // Number of threads from input
struct SFE{
int turn;
int thread;
};
void *thread_function(void *void_ptr_argv)
{
SFE *threadNum = (SFE *) void_ptr_argv;
pthread_mutex_lock(&bsem);
// if its not our turn then wait
while(threadNum->turn != threadNum->thread){
pthread_cond_wait(&waitTurn, &bsem);
}
pthread_mutex_unlock(&bsem);
std::cout << "I am Thread " << threadNum->turn << std::endl;
pthread_mutex_lock(&bsem);
threadNum->turn++;
pthread_cond_broadcast(&waitTurn);
pthread_mutex_unlock(&bsem);
return nullptr;
}
int main()
{
std::cin >> nthreads;
pthread_mutex_init(&bsem, NULL); // Initialize bsem to 1
pthread_t *tid= new pthread_t[nthreads];
SFE threadNumber;
threadNumber.turn = 0;
for(int i=0;i<nthreads;i++)
{
// initialize the thread number here (remember to follow the rules from the specifications of the assignment)
threadNumber.thread = i;
pthread_create(&tid[i], nullptr, thread_function, (void*)&threadNumber);
}
for(int i = 0; i < nthreads; i++)
{
pthread_join(tid[i], nullptr);
}
return 0;
}
I am expecting a simple way to solve my problem

Answer 1

Think about threadNum->thread. threadNum is an unique object, thus each thread gets an unspecified number threadNum->thread between 0 and nthreads. Only the last thread gets the correct number nthreads - 1 .
You should update
struct SFE{
int *turn;
int thread;
};
Allocate the array SFE threadNum[nthread] and pass &threadNum[i] to i-th thread.
int turn = 0;
for(int i=0;i<nthreads;i++)
{
// initialize the thread number here (remember to follow the rules from the specifications of the assignment)
threadNumber[i].turn = &turn;
threadNumber[i].thread = i;
pthread_create(&tid[i], nullptr, thread_function, &threadNumber[i]);
}
Your code is C-ism. This code w/o iostream and new is a clean C. If you use C++, all will be much easier.