Losing my mind on a simple seg fault caused by pthread_create() - c

Question

In this code, I'm trying to create an array of threads. I've set the pthreads value to 1. In the for loop, the address, ID, and "created" gets printed, but the function never seems to execute as I don't get a print.
The seg fault actually happens at pthread_join at the bottom, but it certainly has to be caused by the creation since the function never runs, right? producers[0] is the only thread since I'm just testing 1. The create function passes an (ID address, NULL, the void * function(), and void* arguments) like it's supposed to. It has to be something obvious but I've tried to figure it out for so long I'm empty.
typedef struct ThreadStruct {
int threadIndex;
} ThreadStruct;
void *producer(void* ts){
printf("in producer\n");
FILE* inputfp = threadstruct->inputFiles[0];
hostname = (char*)malloc((MAXNAME+1)*sizeof(char));
while(fscanf(inputfp, hostname) > 0){
printf("%s",hostname);
}
return 0;
}
int main(int argc, char *argv[]){
int pthreads = atoi(argv[1]); //always 1
ThreadStruct threadstruct;
pthread_t producers[pthreads];
for(int i=0;i<pthreads;i++){
printf("in pthread loop\n");
printf("%p \n",&producers[i]);
printf("%ld \n",producers[i]);
pthread_create(&producers[i], NULL, producer, (void *) &threadstruct);
}
pthread_join(producers[0], NULL);
}

Answer 1

Your code works in my side and would not produce the seg fault.
Here is the print out info:
$ ./pthread
in pthread loop
0xffffcb70
6444554784
in pthread loop
in producer
0xffffcb78
64
in pthread loop
in producer
0xffffcb80
1
in pthread loop
in producer
0xffffcb88
4299166064
in pthread loop
in producer
0xffffcb90
6443761969
in pthread loop
in producer
0xffffcb98
6445451520
in pthread loop
in producer
0xffffcba0
314761761601
in producer
exit main thread
Your code here:
#include<stdio.h>
#include<stdlib.h>
#include<pthread.h>
typedef struct ThreadStruct {
int threadIndex;
} ThreadStruct;
void *producer(void* ts){
printf("in producer\n");
return 0;
}
int main(int argc, char *argv[]){
int pthreads = 7;
ThreadStruct threadstruct;
pthread_t producers[pthreads];
for(int i=0;i<pthreads;i++){
printf("in pthread loop\n");
printf("%p \n",&producers[i]);
printf("%ld \n",producers[i]);
pthread_create(&producers[i], NULL, producer, (void *) &threadstruct);
}
pthread_join(producers[0], NULL);
printf("exit main thread\n");
}

Answer 2

you don't seem to check if the thread is actually created or not, in other words you don't seem to validate the return type of pthread_create and straight calling pthread_join probably leading to Undefined behavior, in case pthread_create fails.
pthread_create(&producers[i], NULL, producer, (void *) &threadstruct);
from pthread_join
The pthread_join() function shall fail if:
EINVAL The implementation has detected that the value specified by thread does not refer to a joinable thread.
ESRCH No thread could be found corresponding to that specified by the given thread ID.
however there are cases where pthread_join with invalid thread handle seg faults.
a piece of extract from the link above
"*Passing invalid handle to pthread_join is like passing invalid pointer to a system call.
The implementation may detect it and signal it in errno, but it may crash as
well.
There are 2 different POSIX threads implementations on Red Hat Linux
linuxthreads, where pthread_t handle is a small integer (and the number of
threads is substantially limited)
NPTL (the default, pthread_t is internally a pointer so that there are no
arbitrary thread limits)
You can request the old-fashioned threading library with LD_ASSUME_KERNEL=2.4.19
in the environment.
For NPTL where pthread_t is a pointer, pthread_join detects some invalid
handles where it can be done cheaply. But detecting all possible invalid
handles would be very costly (the implementation would basically have to take
a global lock and iterate over all currently running threads, comparing the
handle with each of them. With say 100000 running threads you can see how
costly it is).
This testcase works on SuSE since SuSE only ships the old-fashioned non-scalable
linuxthreads implementation.*"
from pthead_create
RETURN VALUE
On success, pthread_create() returns 0; on error, it returns an error number, and the contents of *thread are undefined.
perhaps something like this
if( pthread_create(&producers[i], NULL, producer, (void *) &threadstruct) ) {
perror("something wrong .. ");
exit(1);
}

Answer 3

Firstly check the return value of pthread_create() to check whether it was successful or not. For e.g
int ret = pthread_create(&producers[i], NULL, producer, (void *) &threadstruct);
if(ret) {
fprintf(stderr, "failed to create thread %s\n",strerror(ret));
exit(EXIT_FAILURE);
}
And Also it's advised to use pthread_join() for all the threads not only first thread, as if you want to wait for thread/s to terminate before further processing in main thread as mentioned here. Also check the return value of pthread_join().
Sample Code
#include<stdio.h>
#include<string.h>
#include<stdint.h>
#include<stdlib.h>
#include<pthread.h>
typedef struct ThreadStruct {
int threadIndex;
} ThreadStruct;
void *producer(void* ts){
printf("in producer\n");
return 0;
}
int main(int argc, char *argv[]){
int pthreads = 5;
int ret;
ThreadStruct threadstruct;
pthread_t producers[pthreads];
/* create threads */
for(intptr_t itr = 0;itr < pthreads; itr++){
printf("in pthread loop\n");
//printf("%p \n",&producers[itr]);
//printf("%ld \n",producers[itr]);
ret = pthread_create(&producers[itr], NULL, producer, (void *) &threadstruct);
if (ret) {
fprintf(stderr, "failed to create thread #%ld - %s\n",(long)itr, strerror(ret));
exit(EXIT_FAILURE);
}
}
/* join all threads */
for(intptr_t itr = 0; itr < pthreads; itr++){
printf("In main: joining thread #%ld\n", (long)itr);
ret = pthread_join(producers[itr], NULL);
if (ret) {
fprintf(stderr, "failed to join thread #%ld - %s\n",(long)itr, strerror(ret));
exit(EXIT_FAILURE);
}
}
//pthread_exit();
return 0;
}
it works in my system, hope it works for you also.