具有阻塞读取和非阻塞写入的循环/环形缓冲区？

Question

我正在用户空间中搜索 C 语言的环形缓冲区实现，因此我可以在我的库中使用它。

因为我需要一个环形缓冲区

• 非阻塞写入(=覆盖最旧的数据)
• 如果为空则阻止读取

我搜索了一会儿，记得我曾使用 wait_event_interruptible 和 wake_up_interruptible 在内核模式下做这样的事情。

但是在用户空间中使用了什么，所以我也许可以结合该方法搜索环形缓冲区？我不想重新发明轮子 - 周围有很多环形缓冲区解决方案。

在此先致谢并致以亲切的问候!

编辑:

似乎 pthread_cond_wait 可能等同于 wait_event_interruptible。

Answer 1

用一些代码添加另一个答案，这与我的另一个答案中的 pseudocde 不是 1:1 匹配。将此标记为 wiki 答案，以防有人想要添加评论或进行其他改进。非常简单的ringbuffer的C phtread mutex+condition variable实现:

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

#define RINGBUFFER_SIZE (5)
int ringbuffer[RINGBUFFER_SIZE];
unsigned reader_unread = 0;
unsigned writer_next = 0;
pthread_mutex_t ringbuffer_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t ringbuffer_written_cond = PTHREAD_COND_INITIALIZER;

void process_code(int ch) {
    int counter;
    printf("Processing code %d", ch);
    for(counter=5; counter>0; --counter) {
        putchar('.');
        fflush(stdout);
        sleep(1);
    }
    printf("done.\n");

}

void *reader() {
    pthread_mutex_lock(&ringbuffer_mutex);
    for(;;) {
        if (reader_unread == 0) {
            pthread_cond_wait(&ringbuffer_written_cond, &ringbuffer_mutex);
        }
        if (reader_unread > 0) {

            int ch;
            int pos = writer_next - reader_unread;
            if (pos < 0) pos += RINGBUFFER_SIZE;
            ch = ringbuffer[pos];
            --reader_unread;

            if (ch == EOF) break;

            pthread_mutex_unlock(&ringbuffer_mutex);
            process_code(ch);
            pthread_mutex_lock(&ringbuffer_mutex);
        }
    }
    pthread_mutex_unlock(&ringbuffer_mutex);

    puts("READER THREAD GOT EOF");
    return NULL;
}

void *writer() {
    int ch;
    do {
        int overflow = 0;
        ch = getchar();

        pthread_mutex_lock(&ringbuffer_mutex);

        ringbuffer[writer_next] = ch;

        ++writer_next;
        if (writer_next == RINGBUFFER_SIZE) writer_next = 0;

        if (reader_unread < RINGBUFFER_SIZE) ++reader_unread;
        else overflow = 1;

        pthread_cond_signal(&ringbuffer_written_cond);
        pthread_mutex_unlock(&ringbuffer_mutex);

        if (overflow) puts("WARNING: OVERFLOW!");

    } while(ch != EOF);

    puts("WRITER THREAD GOT EOF");
    return NULL;
}

int main(void)
{
    pthread_t reader_thread, writer_thread;

    puts("Starting threads. Type text and press enter, or type ctrl-d at empty line to quit.");
    pthread_create(&reader_thread, NULL, reader, NULL);
    pthread_create(&writer_thread, NULL, writer, NULL);

    pthread_join(writer_thread, NULL);
    pthread_join(reader_thread, NULL);

    return 0;
}