Question

我阅读了memcached源代码，发现在函数“ static void * conn_timeout_thread（void * arg）”中，某些变量可以在其他线程中更改，但是这里没有锁。
就像“ c-> last_cmd_time”一样，当其他线程从网络获取连接时，它也会更改。如果现在连接超时线程正在读取该变量，那么可能会发生错误吗？代码如下。

#define CONNS_PER_SLICE 100
#define TIMEOUT_MSG_SIZE (1 + sizeof(int))
static void *conn_timeout_thread(void *arg) {
int i;
conn *c;
char buf[TIMEOUT_MSG_SIZE];
rel_time_t oldest_last_cmd;
int sleep_time;
useconds_t timeslice = 1000000 / (max_fds / CONNS_PER_SLICE);

while(1) {
    if (settings.verbose > 2)
        fprintf(stderr, "idle timeout thread at top of connection list\n");

    oldest_last_cmd = current_time;

    for (i = 0; i < max_fds; i++) {
        if ((i % CONNS_PER_SLICE) == 0) {
            if (settings.verbose > 2)
                fprintf(stderr, "idle timeout thread sleeping for %ulus\n",
                    (unsigned int)timeslice);
            usleep(timeslice);
        }

        if (!conns[i])
            continue;

        c = conns[i];

        if (!IS_TCP(c->transport))
            continue;

        if (c->state != conn_new_cmd && c->state != conn_read)
            continue;

        if ((current_time - c->last_cmd_time) > settings.idle_timeout) {
            buf[0] = 't';
            memcpy(&buf[1], &i, sizeof(int));
            if (write(c->thread->notify_send_fd, buf, TIMEOUT_MSG_SIZE)
                != TIMEOUT_MSG_SIZE)
                perror("Failed to write timeout to notify pipe");
        } else {
            if (c->last_cmd_time < oldest_last_cmd)
                oldest_last_cmd = c->last_cmd_time;
        }
    }

    /* This is the soonest we could have another connection time out */
    sleep_time = settings.idle_timeout - (current_time - oldest_last_cmd) + 1;
    if (sleep_time <= 0)
        sleep_time = 1;

    if (settings.verbose > 2)
        fprintf(stderr,
                "idle timeout thread finished pass, sleeping for %ds\n",
                sleep_time);
    usleep((useconds_t) sleep_time * 1000000);
    }
return NULL;
}

memcached连接超时线程线程安全吗？

0 个答案: