Generated by XState Viz: https://xstate.js.org/viz

machine.js

  // Available variables:
  // - Machine
  // - interpret
  // - assign
  // - send
  // - sendParent
  // - spawn
  // - raise
  // - actions
  // - XState (all XState exports)

  const randomInt = (min, max) => Math.floor(Math.random() * (max - min)) + min;

  const lockConfig = {
    createDelayMs: 1000, // 1s
    minHoldTimeMs: 2500, // 2.5s
    checkDelayMs: 500, // 0.5s
    minWaitTimeMs: 1000, // 1s
    maxWaitTimeMs: 3000, // 3s
    waitTimeoutMs: 60 * 1000, // 1 minute
  };

  const lockMachine = Machine(
    {
      id: "CommentLockMachine",
      initial: "initialRead",
      strict: true,
      context: {
        waitTime: 0,
        totalWaitTime: 0,
        totalHeldTime: 0,
      },
      states: {
        initialRead: {
          on: {
            // comment doesn't exist
            NOT_FOUND: "creating",
            // comment exists, have hold
            HELD: "holding",
            // comment exists,
            LOCKED: "acquiring",
          },
        },
        creating: {
          id: "creating",
          initial: "waiting",
          entry: "resetTotalWaitTime",
          states: {
            waiting: {
              entry: "setWaitTime",
              exit: "updateTotalWaitTime",
              on: {
                COMPLETE_WAIT: "searching",
              },
            },
            searching: {
              on: {
                // comment doesn't exist, done waiting
                CREATE: "creating",
                // comment doesn't exist, need to wait
                NOT_FOUND: "waiting",
                // comment exists, try to acquire
                LOCKED: "#acquiring",
                // wait time exceeded time out
                TIMEOUT: "#timed_out",
              },
            },
            creating: {
              on: {
                ACQUIRED: "#acquired",
              },
            },
          },
        },
        acquiring: {
          id: "acquiring",
          // We will only enter this state if the comment exists
          // and it isn't ours so first wait
          initial: "waiting",
          entry: "resetTotalWaitTime",
          states: {
            // Wait random time before attempting to acquire again
            waiting: {
              entry: "setWaitTime",
              exit: "updateTotalWaitTime",
              on: {
                COMPLETE_WAIT: "acquiring",
              },
            },
            acquiring: {
              on: {
                HELD: "#holding",
                // Comment exists, no one has lock
                AVAILABLE: "writing",
                // comment exists, is locked
                LOCKED: "waiting",
                // comment exists, wait timeout exceeded
                TIMEOUT: "#timed_out",
              },
            },
            writing: {
              on: {
                HELD: "#holding",
              },
            },
          },
        },
        // Wait deterministic time before reading lock
        holding: {
          id: "holding",
          initial: "holding",
          context: {
            totalHeldTime: 0,
          },
          entry: "resetTotalHeldTime",
          states: {
            holding: {
              exit: "updateTotalHeldTime",
              on: {
                CHECK_HOLD: "checking",
              },
            },
            // read lock to see if we still have it
            checking: {
              on: {
                ACQUIRED: "#acquired",
                HELD: "holding",
                LOCKED: "#acquiring",
              },
            },
          },
        },
        // final states
        acquired: {
          id: "acquired",
          type: "final",
        },
        timed_out: {
          id: "timed_out",
          type: "final",
        },
      },
    },
    {
      actions: {
        resetTotalHeldTime: assign({
          totalHeldTime: 0,
        }),
        updateTotalHeldTime: assign({
          totalHeldTime: (ctx, evt) => {
            return ctx.totalHeldTime + lockConfig.checkDelayMs;
          },
        }),
        setWaitTime: assign({
          waitTime: (ctx, evt) => {
            return randomInt(lockConfig.minWaitTimeMs, lockConfig.maxWaitTimeMs);
          },
        }),
        resetTotalWaitTime: assign({
          totalWaitTime: 0,
        }),
        updateTotalWaitTime: assign({
          waitTime: 0,
          totalWaitTime: (ctx, evt) => {
            return ctx.totalWaitTime + ctx.waitTime;
          },
        }),
      },
    }
  );