The caveat of thread name length in glibc

Recently, our team met an interesting bug: the process is configured to spawn 16 threads, but only spawns 10 threads in reality. The thread code is like this:

static void *
stat_consumer_thread_run(void *data)
{
    stat_consumer_thread_t *thread = data;
    char thread_name[64];
    snprintf(thread_name, sizeof(thread_name), "stat.consumer.%d",
        thread->id);
    int rc = pthread_setname_np(pthread_self(), thread_name);
    if (rc != 0) {
        return NULL;
    }

    ......
    return NULL;
}

After checking pthread_setname_np manual, we found:

The thread name is a meaningful C language string, whose length is restricted to 16 characters, including the terminating null byte (’\0’).

So thread name is restricted to 16 characters, “stat.consumer.0” ~ “stat.consumer.9” are set successfully, but “stat.consumer.10” ~ “stat.consumer.15” are not, and the corresponding threads are failed to run.