write() udp socket

write() udp socket

[ZHOU Xiaobo]

question No1:
When I call 
ssize_t write(int fd, const void *buf, size_t count);


on a nonblocking UDP socket, is the return value  always equal to 'count'?


question No2:
Can I write() a UDP socket in multiple threads without locking?


thanks


------------------
Sincerely yours
                         ZHOU Xiaobo

Re: write() udp socket

[Huajun Li]

2011/7/23 ZHOU Xiaobo <xb.zhou@qq.com>:
> question No1:
> When I call
> ssize_t write(int fd, const void *buf, size_t count);
>
>
> on a nonblocking UDP socket, is the return value  always equal to 'count'?
>
>

I don't think so.  The function may be interrupt by signal or return
due to other reason, so the return value only represents the size it
writes successfully to the fd.

> question No2:
> Can I write() a UDP socket in multiple threads without locking?
>

In my opinion, you could. However, the receiver may not get what you expected.
>
> thanks
>
>
> ------------------
> Sincerely yours
>                         ZHOU Xiaobo

Re: write() udp socket

[Rick Jones]

On 07/24/2011 01:33 AM, Huajun Li wrote:
> 2011/7/23 ZHOU Xiaobo<xb.zhou@qq.com>:
>> question No1:
>> When I call
>> ssize_t write(int fd, const void *buf, size_t count);
>>
>>
>> on a nonblocking UDP socket, is the return value  always equal to 'count'?
>>
>>
>
> I don't think so.  The function may be interrupt by signal or return
> due to other reason, so the return value only represents the size it
> writes successfully to the fd.

I believe it should either appaear to succeed or fail.  write() best not 
be sending partial UDP datagrams.  That would be "bad."

Re: write() udp socket

[ZHOU Xiaobo]

------------------
Sincerely yours
                         ZHOU Xiaobo
 
 
 
------------------ Original ------------------
From:  "Rick Jones"<rick.jones2@hp.com>;
Date:  Tue, Jul 26, 2011 01:38 AM
To:  "Huajun Li"<huajun.li.lee@gmail.com>;
Cc:  "ZHOU Xiaobo"<xb.zhou@qq.com>; "netdev"<netdev@vger.kernel.org>;
Subject:  Re: write() udp socket
 
On 07/24/2011 01:33 AM, Huajun Li wrote:
> 2011/7/23 ZHOU Xiaobo<xb.zhou@qq.com>:
>> question No1:
>> When I call
>> ssize_t write(int fd, const void *buf, size_t count);
>>
>>
>> on a nonblocking UDP socket, is the return value  always equal to 'count'?
>>
>>
>
> I don't think so.  The function may be interrupt by signal or return
> due to other reason, so the return value only represents the size it
> writes successfully to the fd.

I believe it should either appaear to succeed or fail.  write() best not 
be sending partial UDP datagrams.  That would be "bad."



yeah, the same as I think. If so the answer of Question No.2 is 'yes' too?

Re: write() udp socket

[ZHOU Xiaobo]

------------------
Sincerely yours
                         ZHOU Xiaobo
 
 
 
------------------ Original ------------------
From:  "Huajun Li"<huajun.li.lee@gmail.com>;
Date:  Sun, Jul 24, 2011 04:33 PM
To:  "ZHOU Xiaobo"<xb.zhou@qq.com>;
Cc:  "netdev"<netdev@vger.kernel.org>;
Subject:  Re: write() udp socket
 
2011/7/23 ZHOU Xiaobo <xb.zhou@qq.com>:
> question No1:
> When I call
> ssize_t write(int fd, const void *buf, size_t count);
>
>
> on a nonblocking UDP socket, is the return value  always equal to 'count'?
>
>

I don't think so.  The function may be interrupt by signal or return
due to other reason, so the return value only represents the size it
writes successfully to the fd.



UDP is datagram, so I think it guarantees the 'buffer' in 'write()'  is entirely sent
like an atomic operate.


> question No2:
> Can I write() a UDP socket in multiple threads without locking?
>

In my opinion, you could. However, the receiver may not get what you expected.

what will happen? I only concern whether the application 'buffer' is sent partially which
is unacceptable.

>
> thanks
>
>
> ------------------
> Sincerely yours
>                         ZHOU Xiaobo