Suggestions on message transfer among backends

  I need some function which requires some message exchange among different back-ends （connections).

specially I need a shared hash map and a message queue.  

Message queue:  it should be many writers,  1 reader.   Looks POSIX message queue should be OK, but postgre doesn't use it.  is there any equivalent in PG?  

shared hash map:  the number of items can be fixed and the value can be fixed as well. 

any keywords or explanation will be extremely helpful. 

Thanks