// Buffer-slot state engine of the io_uring video demo.
// Render:  dot -Tsvg state-engine.dot -o state-engine.svg
//
// The BuffState of each ring slot is written and read ONLY by the Proactor
// thread; the single SHOW->FREE transition is triggered by the GUI thread
// clearing the atomic baton (toDisplay_), but observed and enacted here.

digraph BuffState {
  rankdir=LR;
  bgcolor="transparent";
  labelloc="t";
  fontname="sans-serif";
  fontsize=14;
  label="Life-cycle of one buffer »slot«";

  node [shape=circle, fixedsize=true, width=0.9,
        fontname="sans-serif", fontsize=12, style=filled, penwidth=1.4];
  edge [fontname="sans-serif", fontsize=10];

  FREE [fillcolor="#dbe9ff"];
  READ [fillcolor="#ffedcc"];
  FEED [fillcolor="#d8f0d8"];
  SHOW [fillcolor="#e7d8ff"];
  STOP [shape=doublecircle, width=0.85, fillcolor="#ffd6d6"];

  FREE -> READ [label="  submit read\l  addNextReadSubmissions()\l"];
  READ -> FEED [label="  read completed OK\l  handleCompletedRead()\l"];
  READ -> STOP [label="  short read / EOF  ", fontcolor="#a00000", color="#a00000"];
  FEED -> SHOW [label="  publish frame\l  maybeDisplayFrame()\l"];
  SHOW -> FREE [label="  GUI released frame\l  (toDisplay_ == nullptr)\l",
                fontcolor="#5a2ca0", color="#5a2ca0", constraint=false];

  { rank=same; FREE; }
}