pthread_create error code 11 even with a few threads - c

Question

So I basically have code that is basically
pthread_t cpu[10];
while (a certain condition){
for (int i=0;i<10;i++){
pthread_create(&cpu[i],NULL,(a function), NULL);
}
this code should be running about 10 threads at a time however, after running the while loop a certain amount of times it says their is a pthread error with code 11. I know I am running the threads multiple times however, shouldn't only 10 instances be happening?

Answer 1

The limit on threads is being reached because the program is calling pthread_create() in a loop, constantly spawning more threads, without ever calling pthread_join() to clean up the resources of the existing threads. This quickly fills up the process's threads-table, at which point pthread_create() starts to error out because there is no more room in the process's threads-table for any more threads.
To avoid that problem, you need to modify the code so that it only summons a finite (and reasonable -- read: dozens, not hundreds or thousands) number of threads into existence at one time.
A simple calling-pattern to achieve that would look something like this:
pthread_t cpu[10];
while (a certain condition){
// spawn 10 threads
for (int i=0;i<10;i++){
pthread_create(&cpu[i],NULL,(a function), NULL);
}
// at this point all 10 threads are running
// wait until all 10 threads have exited
for (int i=0;i<10;i++){
pthread_join(&cpu[i], NULL);
}
}
Another common (and somewhat more elegant) approach would be to use a thread-pool instead of spawning and joining threads. That's often preferable because it avoids the overhead required to constantly create and then tear down threads, and because it means that as soon as a thread has finished computing job A, it can immediately grab job B out of the pending-jobs-queue and start working on it -- unlike the code shown above, which has to wait for all 10 threads to complete before it can spawn 10 more.

Answer 2

#include <string.h>
int main() {
printf("%s\n", strerror(11));
return 0;
}
Gives on my system: Resource temporarily unavailable
Again on my system: EAGAIN is defined as 11 (errno.h).
man pthread_create states as possible error return codes:
EAGAIN
Insufficient resources to create another thread.
EAGAIN
A system-imposed limit on the number of threads was encountered. There are a number of limits that may trigger this error: ...
The reason for that was already answered by Jeremy Friesner in the comments section above.