On Fri, Oct 02, 2009 at 03:48:02PM -0700, Adam Langley wrote:
> On Fri, Oct 2, 2009 at 3:44 PM, Jacob Mandelson <[email protected]> wrote:
> > The Linux send(2) man page explicitly says the message is all-or-nothing,
>
> I don't think so. It says:
>
> "If the message is too long to pass atomically through the underlying
> protocol, the error EMSGSIZE is returned, and the message is not
> transmitted."
>
> I think the confusion is that the "underlying protocol" for
> SOCK_STREAM isn't atomic. The description of the error is clearer:
>
> "EMSGSIZE: The socket type requires that message be sent atomically,
> and the size of the message to be sent made this impossible."
It also says:
When the message does not fit into the send buffer of the socket,
send() normally blocks, unless the socket has been placed in non-block‐
ing I/O mode. In non-blocking mode it would return EAGAIN in this
case.
Which reads like "all or nothing" to me, though I could imagine a (perverse?)
implementation with each writer having a send buffer lower layer pulling
data from multiple writers' send buffers in an interleaved manner. (But
maybe there's something else which restricts sockets to a single send buffer.)
-- Jacob
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