Returning code from pthread creation in C++ is 11 - c++

Question

I have thread creation problem using Pthread. My code is as follows. I show only some portion due to space constraints.
Main.c create Detectdirection instance and send to the function.
d = new Detectdirection();
while(run)
{
int ret = d->run_parallel(d);
if(ret == -1)
run = false;
}
My Detectdirection Class has two functions to run in parallel:
class Detectdirection{
public:
int run_parallel(void*p);
void *Tracking(void *p);
static void *Tracking_helper(void * p);
void *ReadImage(void *p );
static void *ReadImage_helper(void *p );
private:
pthread_t thread[2];
}
void *Detectdirection::ReadImage(void *p){
Detectdirection *app = (Detectdirection*)p;
while(run){
}
pthread_exit(NULL);
}
void *Detectdirection::Tracking(void *p){
Detectdirection *app = (Detectdirection*)p;
while(run){
}
pthread_exit(NULL);
}
void *Detectdirection::Tracking_helper(void *p){
Detectdirection *app = (Detectdirection*)p;
return ((Detectdirection*)p)->Tracking(app);
}
void *Detectdirection::ReadImage_helper(void *p ){
Detectdirection *app = (Detectdirection*)p;
return ((Detectdirection*)p)->ReadImage(app);
}
int Detectdirection::run_parallel(void* p){
Detectdirection *app = (Detectdirection*)p;
int rc = pthread_create(&thread[0], NULL, app->ReadImage_helper, app);
if (rc) {
printf("ERROR; return code from pthread_create() is %d\n", rc);
return -1;
}
rc = pthread_create(&thread[1], NULL, app->Tracking_helper, app);
if (rc) {
printf("ERROR; return code from pthread_create() is %d\n", rc);
return -1;
}
return 0;
}
Compile is ok and when I run, I have thread creation error. That sort of return type 11 happens only when many threads are created. But now I create only two thread and I have that error. What could be wrong?

Answer 1

I believe your are getting EAGAIN (based on the error code 11). That (obivously) means your system doesn't have enough resources to create threads anymore.
POSIX documentation says:
[EAGAIN] The system lacked the necessary resources to create another
thread, or the system-imposed limit on the total number of threads in
a process {PTHREAD_THREADS_MAX} would be exceeded.
I am not quite sure the following is true.
But now I create only two thread and I have that error. What could be wrong?
Here,
while(run)
{
int ret = d->run_parallel(d);
if(ret == -1)
run = false;
}
You are creating in a loop and each call d->run_parallel() creates two threads. So, you are potentially creating infinite number of threads
as the loop only breaks when pthread_create() fails. So, you may want to look at this loop carefully whether you really want to do as it is right now.
You don't seem to join with the threads you create. So, you could detach the threads so that thread-specific resources are released immediately when the thread(s) exit.
You can do:
pthread_detach(pthread_self());
in both ReadImage_helper() and Tracking_helper() functions to detach them. This could potentially solve your resource issue.
If it's still present then you have to look at ways to limit the number of threads that are simultaneously running on your system. One possible option is to use thread pools -- create a fixed number of threads and assign them new tasks as the threads complete their current task(s).