P. Oscar Boykin wrote:
According to this:
http://groups.google.com/group/comp.protocols.tcp-ip/browse_thread/thread/7f695ec1d8f83253/b11f53da207558cc?lnk=st&q=sending+and+receiving+sockets+simultaneously+linux&rnum=14&hl=en#b11f53da207558cc
It is safe to use a socket in most unices in two threads if one does only
reading and one does only writing.
Is this true of Mono/C#?
The only documentation I can find is from Socket:
"All public static members of this type are safe for multithreaded
operations. No instance members are guaranteed to be thread safe."
Which I believe is boilerplate, but would imply that it might not be
safe to
read in one thread and write in another.
The boilerplate just states that the implementation of
a certain class is not thread safe. It doesn't mean that
the underlying technology is not thread safe.
My experiments suggest that reading in one thread and writing in another
works in mono (tested with UDP), but I am wondering if there is an
"official" position. Is this unclear in the .Net class library? Might it
stop working in the future and not be considered a bug?
It's common sense that [Begin|End]Receive[From] and
[Begin|End]Send[To] are thread safe.
[In MS.NET 2.0, the Socket class is even marked as thread safe.]
The case I am working with is the following: two hosts have a socket
between
them. At any time one or the other may send data. What is the lowest
latency way to make sure that data is sent quickly and received quickly.
Being strict about the documentation would imply it is not safe to do a
blocking read in one thread while sending in another thread. Thus, it
seems
that polling (or select) is required, both of which introduce latency.
If anyone else has some good pointers on how to use one socket to send and
receive without polling or using the asynchronous methods I would be happy
to learn of them (polling introduces latency and the asynchronous methods
often lead to deadlocks I guess due to their internal use of threadpools).
Supposing the reads & writes are highly interdependent, using
asynchronous methods is the fastest way. Having separate threads
for reading and writing needs thread synchronization and leads
to a context switch.
The async methods used by the Socket class are handled differently
by the runtime. They are not invoked from the generic TP. The Socket
IO is handled by a specialized thread using AIO APIs.
BTW, the TP issues have been fixed in the meanwhile:
http://www.mono-project.com/Article:ThreadPool_Deadlocks
(see "Long Term Solutions")
Robert
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