Message Passing

Communication models, erlang messaging, concurracy

What is significant for synchronous communication?

the send operation blocks and waits for the receive operation

What is significant for asynchronous communication?

a sender can continue without waiting for the receive operation

What is true for asynchronous communication?

sender does not block waiting for receiver

Can a synchronous communication interface be used in an asynchronous way?

yes, by performing the send operation in a separate thread

What is the difference between the two nodes that are communicating using a stream socket API?

nothing, they have equal rights and responsibilities

The Erlang call gen tcp:recv(Socket, 0) will return:

the first part (possibly the whole) message sent to Socket

A server using a stream socket API can communicate with several clients and separate the streams by:

creating a new stream socket for each connecting client

How do Erlang processes communicate?

asynchronous message passing

Does Erlang provide a form of location transparency?

Yes - a process can use a process identifier without having to know the address of the node where the process lives.

How is the destination defined in an Erlang send operation?

as a process identifier or a local or remote registered name

What will prevent an Erlang process from sending a message to a process on another Erlang node?

the two nodes do not have the same secret cookie

Message sending in Erlang provides the following semantics:

best effort FIFO delivery of message

Can we have a circular construction in Erlang?

yes, processes can refer to each other in a circular way

What happens with Erlang processes that are suspended on a receive statement but no longer referenced by any process?

they will remain if registered, otherwise removed by the garbage collector

Assume we have three Erlang processes: A, B and C.

Also assume that A sends a message, m1, to B and then sends a message, m2, to C. B is suspended, waiting for a message from A that it will send to C.

What is guaranteed by the Erlang semantics.

no guarantees on receiving nor ordering of messages