Why does SSL_write in BoringSSL cause a 2-second delay?

I’m developing an application on Android 10 using C code, compiled into a .so library. The application sends data using BoringSSL’s SSL_write() in blocking mode.

SSL_write() returns successfully, but Wireshark captures the corresponding Application Data packet with a 2-second delay.
This delay occurs intermittently, roughly 1 in 10-20 attempts.

Code Example:
Here is the code snippet that sends data using SSL.

// set to blocking before write
fcntl(g_ssl_sock_id, F_SETFL, flags & (~O_NONBLOCK));

// Since the original function contains other judgment logic such as TCP, the SSL_write code is extracted separately
static int ssl_write()
{
    int send_len, len = total_len;;
    unsigned char *cur_p = send_data;
    print_timestamp("Before SSL_write");

    while (len > 0)
    {
        send_len = (len > TCP_MAX_SSL_SEND_BUFFER_SIZE) ? TCP_MAX_SSL_SEND_BUFFER_SIZE : len;

        ret = SSL_write((SSL *)ssl_handle.handle, cur_p, send_len);
        print_timestamp("After SSL_write");

        if (ret != send_len)
        {
            LOG("SslSend data error: %d, exp: %d\n", ret, send_len);
            memset(send_data, 0, total_len);
            if (dyn_allocate)
            {
                uai_free(send_data);
            }
            return (g_err_code = UAI_ERROR);
        }

        len -= send_len;
        cur_p += send_len;
    }

    memset(send_data, 0, total_len);
    if (dyn_allocate)
    {
        uai_free(send_data);
    }
    return (g_err_code = UAI_OK);
}

Other settings:

//setsockopt TCP_NODELAY to disable nagle algorithm but still not work.

Log infomation:

<2024-10-16 11:13:55.505-0574700106>[info_callback]:SSL state: SSLv3 write client hello A
<2024-10-16 11:14:00.909-0574705510>[print_timestamp]:BBB ssl time=[2024-10-16 11:14:00.909600], Before SSL_write
<2024-10-16 11:14:00.909-0574705510>[print_timestamp]:BBB ssl time=[2024-10-16 11:14:00.909912], After SSL_write
E<2024-10-16 11:14:02.890-0574707490>info_callback]:SSL alert: close notify

enter image description here

Has anyone encountered a similar issue or know what might be causing this? I’d appreciate any insights or suggestions to troubleshoot this further. Thanks in advance!

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