问这是实现不带互斥的异步消息队列的安全方法吗？

EN

typedef struct MessageQueueElement {
    Message message;
    struct MessageQueueElement *next;
} MessageQueueElement;

typedef struct MessageQueue { //singly-linked list as a queue
    MessageQueueElement *first;
    MessageQueueElement *last;
    bool sending;
} MessageQueue;

void createMessageQueue(MessageQueue *this) {
    this->first = malloc(sizeof(MessageQueueElement));
    this->last = this->first;
    this->sending = false;
}

void sendMessage(MessageQueue *this, Message *message) {
    while (this->sending);
    //do nothing while this function is called from another thread

    this->sending = true;
    this->last->message = *message;
    this->last = this->last->next = malloc(sizeof(MessageQueueElement));
    //add a message to the queue

    this->sending = false;
}

int waitMessage(MessageQueue *this, int (*readMessage)(unsigned, unsigned, void *)) {
    while (this->first == this->last);
    //do nothing while the queue is empty

    int n = readMessage(this->first->message.type, this->first->message.code, this->first->message.data);
    MessageQueueElement *temp = this->first;
    this->first = this->first->next;
    free(temp);
    return n;
}

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <limits.h>
#include <math.h>
#include <pthread.h>

#define EXIT_MESSAGE 0
#define THREAD_MESSAGE 1
#define EXIT 0
#define CONTINUE 1

int readMessage(size_t type, size_t code, void *data) {
    if (type == THREAD_MESSAGE) {
        printf("message from thread %d: %s\n", code, (char *)data);
        free(data);
    } else {
        return EXIT;
    }
    return CONTINUE;
}

MessageQueue mq;
int nThreads;
int counter = 0;

void *worker(void *p) {
    double pi = 0.0;
    for (int i = 0; i < 10; i += 1) {
        for (int j = 0; j < 100000; j += 1) {
            double n = i * 100000.0 + j;
            pi += (4.0 / (8.0 * n + 1.0) - 2.0 / (8.0 * n + 4.0) - 1.0 / (8.0 * n + 5.0) - 1.0 / (8.0 * n + 6.0)) / pow(16.0, n);
        }
        char *s = malloc(100);
        sprintf(s, "calculating pi... %d percent complete", (i + 1) * 10);
        sendMessage(&mq, &(Message){.type = THREAD_MESSAGE, .code = (int)p, .data = s});
    }
    char *s = malloc(100);
    sprintf(s, "pi equals %.8f", pi);
    sendMessage(&mq, &(Message){.type = THREAD_MESSAGE, .code = (int)p, .data = s});
    counter += 1;
    if (counter == nThreads) {
        sendMessage(&mq, &(Message){.type = EXIT_MESSAGE});
    }
}


int main(int argc, char **argv) {
    nThreads = atoi(argv[1]);
    createMessageQueue(&mq);

    pthread_t threads[nThreads];
    for (int i = 0; i < nThreads; i += 1) {
        pthread_create(&threads[i], NULL, worker, (void *)i);
    }
    while (waitMessage(&mq, readMessage));
    for (int i = 0; i < nThreads; i += 1) {
        pthread_join(threads[i], NULL);
    }
    return 0;
}