Is socket.send thread safe?

[Dmitry Olshansky]

On Monday, 26 March 2018 at 16:14:31 UTC, Jonathan wrote:
> Can I send data over an std.socket on multiple threads without 
> manual mutexing?
>
> If not, can I send data on a separate thread than receive?
>
> The docs for std.socket say nothing of it (which I guess means 
> I should assume it is not thread safe but...).

It’s thin-wrapper over system interface.

It’s thread-safe in that system will not topple over, you will 
likely get some interleaving of data.

HOWEVER: there is such a thing as short-writes, which means that 
since OS buffer may fill up it could write less then you intended 
to and return that amount. It certainly happens with O_NONBLOCK.
In normal blocking mode it might work, but in general it’s a bad 
idea to do writes to a single socket from multiple threads w/o 
some coordination s.t. only can do it at any given time.

Lastly as far as guarantees go, POSIX doesn’t state that 2 writes 
will be interleaved “exactly”, it may for instance splice them 
zebra-style by some chunk size and I could imagine why (on long 
buffers).

My suggestion is to have a queue of messages and a thread to send 
them. You might also want to check and see if there is a better 
protocol then TCP to take advantage of unordered messages. I 
think there is at least RDP (reliable datagram protocol) on Linux 
that might fit the bill.

>
> Thanks!