Async Models — Simple

flowchart LR
  T[Threads + blocking]
  CB[Callbacks]
  FUT[Futures / Promises]
  ASYNC[async / await]
  COR[Coroutines / fibers / virtual threads]
  ACT[Actors / channels]
  RX[Reactive streams]

  T --> CB --> FUT --> ASYNC --> COR
  FUT --> ACT
  FUT --> RX

  classDef p fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
  class T,CB,FUT,ASYNC,COR,ACT,RX p;

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class T,CB,FUT,ASYNC,COR,ACT,RX service;

Different ways to wait for something without blocking a whole OS thread. Each model trades off ergonomics, performance, and error-handling differently.