Which flow management tool works closer to hardware and offers more fine-tuning?

In iOS, to manage threads, there are several tools, but the most low-level and close to hardware is POSIX Threads (pthread). This is a standard thread library providing fine control over thread creation, synchronization, and management.

At the same time, higher-level tools like Grand Central Dispatch (GCD) and Operation Queues offer convenient abstractions but hide implementation details.

If fine-tuned control over threads is needed, pthread is used. For example, threads can be explicitly created, their priorities managed, and synchronization used.

Example of creating a thread with pthread:

#include <pthread.h>
#include <stdio.h>

void* threadFunc(void* arg) {
    printf("Hello from thread!\n");
    return NULL;
}

int main() {
    pthread_t thread;
    pthread_create(&thread, NULL, threadFunc, NULL);
    pthread_join(thread, NULL);
    return 0;
}

Thus, pthread works closer to hardware and provides more fine-tuned thread control.