Incomprehensible result of a multithread code - c

Question

I will start a C Programming project that will be used multithread. Before I start the project, I have written a code for practice. My purpose is to see how mutex and threads works. However it is not work properly. Here is the code:
#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>
#include <string.h>
pthread_mutex_t myMutex;
char myStrings[100][30];
int i=0;
void *PrintThread1()
{
printf("this is initial of FIRST Thread\n");
for (int j=0; j<33; j++) {
pthread_mutex_lock(&myMutex);
strcpy(myStrings[i], "This is FIRST thread");
i++;
pthread_mutex_unlock(&myMutex);
}
pthread_exit(NULL);
}
void *PrintThread2()
{
printf("this is initial of SECOND Thread\n");
for (int j=0; j<33; j++) {
pthread_mutex_lock(&myMutex);
strcpy(myStrings[i], "This is SECOND thread");
i++;
pthread_mutex_unlock(&myMutex);
}
pthread_exit(NULL);
}
void *PrintThread3()
{
printf("this is initial of THIRD Thread\n");
for (int j=0; j<33; j++) {
pthread_mutex_lock(&myMutex);
strcpy(myStrings[i], "This is THIRD thread");
i++;
pthread_mutex_unlock(&myMutex);
}
pthread_exit(NULL);
}
int main(int argc, char *argv[])
{
pthread_t firstThread, secondThread, thirdThread;
//pthread_attr_t attr;
pthread_mutex_init(&myMutex, NULL);
//pthread_attr_init(&attr);
//pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
int ft;
ft = pthread_create(&firstThread, NULL, PrintThread1(), NULL);
if (ft){
printf("ERROR; return code from pthread_create() is %d\n", ft);
exit(-1);
}
ft = pthread_create(&secondThread, NULL, PrintThread2(), NULL);
if (ft){
printf("ERROR; return code from pthread_create() is %d\n", ft);
exit(-1);
}
ft = pthread_create(&thirdThread, NULL, PrintThread3(), NULL);
if (ft){
printf("ERROR; return code from pthread_create() is %d\n", ft);
exit(-1);
}
pthread_join(firstThread, NULL);
pthread_join(secondThread, NULL);
pthread_join(thirdThread, NULL);
pthread_mutex_destroy(&myMutex);
for (int j=0;j<100; j++) {
printf("String[%d] = %s\n",j,myStrings[j]);
}
printf("\n");
pthread_exit(NULL);
return -1;
}
When I execute this code, my result is:
this is initial of FIRST Thread
Program ended with exit code: 0
I can't figure out the mistake.

Answer 1

ft = pthread_create(&firstThread, NULL, PrintThread1(), NULL);
should read
ft = pthread_create(&firstThread, NULL, PrintThread1, NULL);
and similarly for all your pthread_create calls.
To use pthread_create, you need to pass it the address of a thread-start routine, which you do in C by writing the name of a function without the function-call parentheses.
As you have written it, you call the intended thread-start routine, on the main thread, and pass whatever it returns to pthread_create to be the thread-start routine. But it never returns, because it calls pthread_exit, which (since pthread_create hasn't been called yet, so there is only one thread) terminates the entire program.
Unfortunately, you have to crank the warnings way up before the compiler will catch this mistake, and even then it's not super clear what the problem is:
$ gcc -std=c99 -Wall -pedantic -pthread test.c
test.c: In function ‘main’:
test.c:60:45: warning: ISO C forbids passing argument 3
of ‘pthread_create’ between function pointer and ‘void *’ [-Wpedantic]
ft = pthread_create(&firstThread, NULL, PrintThread1(), NULL);
^
Without -pedantic, no complaint.