user: Hello there. Can you provide me with an implementation of a conditional variable in C using semaphores and mutexes?

assistant: Sure! Here is an example implementation of a conditional variable using semaphores and mutexes in C:

```c
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>

#define MAX_THREADS 2

int count = 0;
sem_t sem;
pthread_mutex_t mutex;
pthread_cond_t cond;

void *thread_function(void *arg)
{
    int thread_id = *((int *) arg);

    pthread_mutex_lock(&mutex); // lock mutex

    while (count < 10) {
        while (count % MAX_THREADS != thread_id) { // check condition
            pthread_cond_wait(&cond, &mutex); // wait for signal
        }

        // critical section
        printf(“Thread %d: count = %d\n”, thread_id, count);
        count++;
        sem_post(&sem); // signal the waiting thread
    }

    pthread_mutex_unlock(&mutex); // unlock mutex
}

int main()
{
    int i;
    pthread_t threads[MAX_THREADS];

    sem_init(&sem, 0, 0); // initialize semaphore
    pthread_mutex_init(&mutex, NULL); // initialize mutex
    pthread_cond_init(&cond, NULL); // initialize conditional variable

    int arg;
    for (i = 0; i < MAX_THREADS; i++) {
        arg = (int*) malloc(sizeof(*arg));
        *arg = i;
        pthread_create(&threads[i], NULL, thread_function, arg); // create threads
    }

    for (i = 0; i < MAX_THREADS; i++) {
        pthread_join(threads[i], NULL); // join threads
    }

    sem_destroy(&sem); // destroy semaphore
    pthread_mutex_destroy(&mutex); // destroy mutex
    pthread_cond_destroy(&cond); // destroy conditional variable

    return 0;
}
```

This code is a multi-threaded program that prints the count from 1 to 10 using a semaphore and a mutex to provide synchronization between threads.

The code creates `MAX_THREADS` threads, where each thread increments the count by 1. It uses a semaphore and a mutex to ensure that only one thread can increment the count at a time, preventing race conditions and ensuring that the correct count is printed.

When a thread increments the count, it increments the semaphore, allowing the next thread in line to enter the critical section. The thread then waits for the semaphore to be posted and then enters the critical section again. This process continues until all threads have printed the count.

user: Now implement the similar things in Rust

assistant: In Rust, a conditional variable is implemented using a combination of a Mutex and a Condvar from the std::sync module. Here is an example implementation using semaphores and mutexes:

```rust

use std::sync::{Arc, Mutex, Condvar};
use std::thread;

fn main() {
    let data = Arc::new((Mutex::new(false), Condvar::new()));

    let data_clone = data.clone();
    let thread_one = thread::spawn(move || {
        let (lock, cvar) = &*data_clone;
        let mut started = lock.lock().unwrap();
        while !*started {
            started = cvar.wait(started).unwrap();
        }
        println!("Thread one started!");
    });

    let data_clone = data.clone();
    let thread_two = thread::spawn(move || {
        let (lock, cvar) = &*data_clone;
        let mut started = lock.lock().unwrap();
        *started = true;
        cvar.notify_all();
        println!("Thread two started!");
    });

    thread_one.join().unwrap();
    thread_two.join().unwrap();
}
```

In this example, we create a shared data structure data that consists of a `Mutex` and a `Condvar`. The `Mutex` is used to synchronize access to the shared boolean started, while the `Condvar` is used to notify waiting threads when the boolean is set to true.

We then create two threads, thread_one and thread_two. thread_one waits on the Condvar until the boolean started is set to true, while thread_two sets the boolean to true and notifies all waiting threads on the `Condvar`.

Note that we use Arc to share ownership of the data structure between threads, and move closures to transfer ownership of the Arc to each thread.