Add proposed fluid syntax for select statement in Fluid's implementation of CSP

[abhinavarora]

No description provided.

[helinwang]

I think we need a way to differentiate the following two cases:

  select {
    case ch1 <- x:
      x := x + 1
    case y <- ch2:
      fmt.Println("Received on channel")
  }

  select {
    case ch1 <- x:
      x := x + 1
  }

  select {
    case y <- ch2:
      fmt.Println("Received on channel")
   }

The first one means wait for either of the case unblock, and continue. The second one means wait for the first unblock, and then wait for the second unblock. But I think the proposed Python syntax can't differentiate between the two case.

[kavyasrinet]

I agree with this as well, I think the default case in select should be the first example i.e. wait for either of the cases to unblock and if multiple cases unblock at the same time, we decide which block to execute pseudo-randomly. Otherwise execute the case that unblocked first.

[abhinavarora]

Sorry my mistake. There is a typo in the code. The code should be sel =fluid.select(). This way, the code can differentiate between the two cases. For the first case the code will be

sel1 = fluid.select()
with sel1.case(ch1, 'w', x):
    ...
    ...

with sel1.case(ch2, 'r', y):
    ...
    ...

For the second case the code will be like this

sel1 = fluid.select()
with sel1.case(ch1, 'w', x):
    ...
    ...

sel2 = fluid.select()
with sel2.case(ch2, 'r', y):
    ...
    ...

[helinwang]

An alternative to consider: sel.case(ch1.recv(x)) and sel.case(ch2.send(Y)).

[kavyasrinet]

My proposal is similar -- Defining the send and recv (write/read) for the Channel as @helinwang proposed above, or writing out send and recv as separate methods:

x = sel.case(fluid.recv(ch1))
sel.case(fluid.send(ch2, Y))

The methods can have the definition like:

void send(Channel* channel, Element* val)

Element* recv(Channel* channel)

[abhinavarora]

I agree the C++ syntax should look like the one that you mentioned above. I am not sure how we would be able to implement sel.case(ch1.recv(x)) in python. This is because ch1.recv(x) can also be called in a standalone fashion, outside of select. I think this might depend on how we design the select operator in Paddle.

[helinwang]

Sorry for the late reply!

I have not find recv design in this doc, but I think ch1.recv(x) should return a var, so it could work both in standalone and in select.

[kavyasrinet]

I agree with @helinwang 's proposal as well.

[wangkuiyi]

I agree with @helinwang as well. I am approving this PR so we could merge it, together with @kavyasrinet 's PR on send/recv syntax. Then, let us rethink about them.

[wangkuiyi]

I agree with @helinwang as well. I am approving this PR so we could merge it, together with @kavyasrinet 's PR on send/recv syntax. Then, let us rethink about them.