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--- language:langs:dflow [2023/02/11 12:04]
rajit [Deterministic and non-deterministic merge]
+++ language:langs:dflow [2024/01/07 11:24] (current)
rajit [Clusters and Ordering]
@@ Line 196: / Line 196: @@
 </code>
+Dataflow clusters are hints to the implementation that these dataflow elements should be grouped together---for example, by having a single control that is shared by all the elements of the cluster.
+Finally, consider the following dataflow example:
+<code act>
+dataflow {
+    a + b -> c; // produce an output on channel c
+    d + e -> out  // sum d and e and produce the output on out
+ }
+</code>
+Furthermore, suppose that the ''c'' output is passed to another process where it is transformed to a new value, and it is this new value that is provided on channel ''e'' that is part of this dataflow block.
+When optimizing the dataflow block, one may decide to group the control for the two dataflow elements. However, doing so would result in deadlock, because the combined dataflow block would wait for inputs to arrive on ''a'', ''b'', ''d'', and ''e''  //before producing an output on ''c''//. It is not possible to determine that ''e'' in fact depends on ''c'' without a full analysis of the entire ACT program.
+To simplify optimizations, the dataflow language also supports the ''order'' directive as the first item in the dataflow block. The same example above would be specified:
+<code act>
+dataflow {
+  order {
+     c < e    // c must be produced before e is available
+   }
+   a + b -> c;
+   d + e -> out
+ }
+</code>
+In general, the order block contains a semi-colon separated list of directives. Each directive is a list of comma-separated channels followed by ''<'' followed by a second comma-separated list of channels. The directive means that all the channels in the first group must produce outputs before any of the channels in the second group can receive inputs.
+====== Syntactic replication ======
+The dataflow sub-language has support for syntactic replication for splits, merges, mixers, and arbiters. For a split, the output side can use syntactic replication; for the others, the input side can use syntactic replication.
+For example, the following syntax is legal (assuming everything is of the right type):
+<code act>
+dataflow {
+  {ctrl} l -> (, i : 8 : out[i])
+ }
+</code>