Simplify pool id internals, allow manual assignment

README.md

@@ -368,10 +368,9 @@ const tasks = {
 
 ## Re-using ports
 
-Each `send` and `receive` port pair only support **one** `ConcurrentTask.Pool` subscribed at a time.
-**Weird** things can happen if you have **two or more** `ConcurrentTask.Pool`s using the same ports at the same time.
+For most cases a single `ConcurrentTask.Pool` is paired a `send` and `receive` port pair.
 
-Generally this should not be needed, but if you have a use-case, please leave an [issue](https://github.com/andrewMacmurray/elm-concurrent-task/issues).
+If you need multiple `Pool`s subscribed to a port pair at the same time or need to continually instantiate new `Pool`s (e.g. switching between pages), make sure each pool has a unique id with `ConcurrentTask.withPoolId`. Otherwise `Pool`s may receive results for other pools which can lead to some confusing states!
 
 ## Develop Locally
 

runner/index.ts

@@ -13,18 +13,10 @@ export * from "./http/index.js";
 export * from "./browser/index.js";
 
 export interface ElmPorts {
-  send: {
-    subscribe: (
-      callback: (defs: TaskDefinition[] | Command) => Promise<void>
-    ) => void;
-  };
-  receive: { send: (result: TaskResult[] | PoolId) => void };
+  send: { subscribe: (callback: (defs: TaskDefinition[]) => Promise<void>) => void; };
+  receive: { send: (result: TaskResult[]) => void };
 }
 
-export type Command = { command: "identify-pool" };
-
-export type PoolId = { poolId: number };
-
 export type Tasks = { [fn: string]: (arg: any) => any };
 
 export interface TaskDefinition {
@@ -128,69 +120,49 @@ export function register(options: Options): void {
   const tasks = createTasks(options);
   const subscribe = options.ports.send.subscribe;
   const send = options.ports.receive.send;
-  let poolId = 0;
-
-  function nextPoolId() {
-    poolId = cycleInt({ max: 1000 }, poolId);
-  }
 
   subscribe(async (payload) => {
-    if ("command" in payload) {
-      switch (payload.command) {
-        case "identify-pool": {
-          // The Promise.resolve wrapper here prevents a race condition in Elm where sometimes the Model is not updated in time before the poolId is received
-          return Promise.resolve().then(() => {
-            send({ poolId });
-            nextPoolId();
-          });
-        }
-        default: {
-          throw new Error(`Unrecognised internal command: ${payload}`);
-        }
-      }
-    } else {
-      const debouncedSend = debounce(send, debounceThreshold(payload));
-
-      for (const def of payload) {
-        if (!tasks[def.function]) {
-          return debouncedSend({
-            attemptId: def.attemptId,
-            taskId: def.taskId,
-            result: {
-              error: {
-                reason: "missing_function",
-                message: `${def.function} is not registered`,
-              },
+    const debouncedSend = debounce(send, debounceThreshold(payload));
+
+    for (const def of payload) {
+      if (!tasks[def.function]) {
+        return debouncedSend({
+          attemptId: def.attemptId,
+          taskId: def.taskId,
+          result: {
+            error: {
+              reason: "missing_function",
+              message: `${def.function} is not registered`,
             },
-          });
-        }
+          },
+        });
       }
+    }
 
-      payload.map(async (def) => {
-        try {
-          logTaskStart(def, options);
-          const result = await tasks[def.function]?.(def.args);
-          logTaskFinish(def, options);
-          debouncedSend({
-            attemptId: def.attemptId,
-            taskId: def.taskId,
-            result: { value: result },
-          });
-        } catch (e) {
-          debouncedSend({
-            attemptId: def.attemptId,
-            taskId: def.taskId,
-            result: {
-              error: {
-                reason: "js_exception",
-                message: `${e.name}: ${e.message}`,
-                raw: e,
-              },
+    payload.map(async (def) => {
+      try {
+        logTaskStart(def, options);
+        const result = await tasks[def.function]?.(def.args);
+        logTaskFinish(def, options);
+        debouncedSend({
+          attemptId: def.attemptId,
+          taskId: def.taskId,
+          result: { value: result },
+        });
+      } catch (e) {
+        debouncedSend({
+          attemptId: def.attemptId,
+          taskId: def.taskId,
+          result: {
+            error: {
+              reason: "js_exception",
+              message: `${e.name}: ${e.message}`,
+              raw: e,
             },
-          });
-        }
-      });
-    }
+          },
+        });
+      }
+    });
   });
 }
 
@@ -271,7 +243,3 @@ function prefixWith(prefix: string, tasks: Tasks): Tasks {
     Object.entries(tasks).map(([key, fn]) => [`${prefix}${key}`, fn])
   );
 }
-
-function cycleInt(options: { max: number }, i: number): number {
-  return i >= options.max ? 0 : i + 1;
-}

src/ConcurrentTask.elm

@@ -9,7 +9,7 @@ module ConcurrentTask exposing
     , race
     , batch, sequence
     , map, andMap, map2, map3, map4, map5
-    , attempt, attemptEach, Response(..), UnexpectedError(..), onProgress, Pool, pool
+    , attempt, attemptEach, Response(..), UnexpectedError(..), onProgress, Pool, pool, withPoolId
     )
 
 {-| A Task similar to `elm/core`'s `Task` but:
@@ -194,7 +194,7 @@ Here's a minimal complete example:
             , subscriptions = subscriptions
             }
 
-@docs attempt, attemptEach, Response, UnexpectedError, onProgress, Pool, pool
+@docs attempt, attemptEach, Response, UnexpectedError, onProgress, Pool, pool, withPoolId
 
 -}
 
@@ -1264,3 +1264,23 @@ Right now it doesn't expose any functionality, but it could be used in the futur
 pool : Pool msg
 pool =
     Internal.pool
+
+
+{-| Add an id to a `Pool`.
+
+Why? Because Pools can be instantiated multiple times (think switching pages in a Single Page App),
+without a unique identifier a ConcurrentTask Pool may end up receiving responses for a ConcurrentTask pool that was previously discarded.
+
+One example is a user switching back and forth between two pages:
+
+    - Page one has a long running task on `init`
+    - The user switches to page 2, then switches back to page 1
+    - A new long running task is started
+    - But the Pool can receive the response from the first long running task (which is unexpected behaviour)
+
+Adding a different id to the `Pool` allows these previous responses to be ignored.
+
+-}
+withPoolId : Int -> Pool msg -> Pool msg
+withPoolId =
+    Internal.withPoolId