Add priority-queue example for TS

patterns-use-cases/priority-queue/priority-queue-typescript/README.md

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+# Priority queue
+
+An example of implementing your own priority queue using Restate state and
+awakeables.
+
+Run the example with `npm run app-dev`.
+
+You can simulate adding work to the queue like this:
+```shell
+# add a single entry
+curl localhost:8080/myService/expensiveMethod/send --json '{"left": 1, "right": 2, "priority": 1}'
+# add lots
+for i in $(seq 1 30); do curl localhost:8080/myService/expensiveMethod/send --json '{"left": 1, "right": 2, "priority": 2}'; done
+```
+
+As you do so, you can observe the logs; in flight requests will increase up to 10, beyond which items will be enqueued.
+
+You can write your own queue item selection logic in `selectAndPopItem`; doing so is outside the scope of this example.

patterns-use-cases/priority-queue/priority-queue-typescript/package.json

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+{
+  "name": "@restatedev/example-pattern-priority-queue",
+  "version": "0.1.0",
+  "description": "A Restate example showing the implementation of a distributed priority queue",
+  "type": "commonjs",
+  "scripts": {
+    "build": "tsc --noEmitOnError",
+    "app-dev": "tsx --watch ./src/app.ts",
+    "app": "tsx ./src/app.ts"
+  },
+  "dependencies": {
+    "@restatedev/restate-sdk": "^1.2.1"
+  },
+  "devDependencies": {
+    "@types/node": "^20.12.7",
+    "tsx": "^4.17.0",
+    "typescript": "^5.0.2"
+  }
+}

patterns-use-cases/priority-queue/priority-queue-typescript/src/app.ts

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+/*
+ * Copyright (c) 2024 - Restate Software, Inc., Restate GmbH
+ *
+ * This file is part of the Restate Examples for the Node.js/TypeScript SDK,
+ * which is released under the MIT license.
+ *
+ * You can find a copy of the license in the file LICENSE
+ * in the root directory of this repository or package or at
+ * https://github.com/restatedev/examples/blob/main/LICENSE
+ */
+
+import { endpoint } from "@restatedev/restate-sdk";
+
+import { queue } from "./queue";
+import { myService } from "./service";
+
+endpoint().bind(queue).bind(myService).listen();

patterns-use-cases/priority-queue/priority-queue-typescript/src/queue.ts

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+/*
+ * Copyright (c) 2024 - Restate Software, Inc., Restate GmbH
+ *
+ * This file is part of the Restate Examples for the Node.js/TypeScript SDK,
+ * which is released under the MIT license.
+ *
+ * You can find a copy of the license in the file LICENSE
+ * in the root directory of this repository or package or at
+ * https://github.com/restatedev/examples/blob/main/LICENSE
+ */
+
+import { object, ObjectContext, TerminalError } from "@restatedev/restate-sdk";
+
+type QueueState = {
+  items: QueueItem[];
+  inFlight: number;
+};
+
+type QueueItem = {
+  awakeable: string;
+  priority: number;
+};
+
+type TickCause =
+  | { type: "done" }
+  | { type: "push"; item: QueueItem }
+  | { type: "drop"; awakeable: string };
+
+// Put your super clever queue fairness algorithm here
+function selectAndPopItem<T>(items: QueueItem[]): QueueItem {
+  let lowest = { priority: Number.MAX_SAFE_INTEGER, index: 0 };
+  for (const [i, item] of items.entries()) {
+    if (item.priority < lowest.priority) {
+      lowest.priority = item.priority;
+      lowest.index = i;
+    }
+  }
+  const [item] = items.splice(lowest.index, 1);
+  return item;
+}
+
+const MAX_IN_FLIGHT = 10;
+
+export const queue = object({
+  name: "queue",
+  handlers: {
+    done: async (ctx: ObjectContext<QueueState>): Promise<void> => {
+      const state = await getState(ctx);
+
+      state.inFlight--;
+
+      tick(ctx, state);
+
+      setState(ctx, state);
+    },
+    push: async (
+      ctx: ObjectContext<QueueState>,
+      item: QueueItem,
+    ): Promise<void> => {
+      const state = await getState(ctx);
+
+      state.items.push(item);
+
+      tick(ctx, state);
+
+      setState(ctx, state);
+    },
+    drop: async (
+      ctx: ObjectContext<QueueState>,
+      awakeable: string,
+    ): Promise<void> => {
+      const state = await getState(ctx);
+
+      const index = state.items.findIndex(
+        (item) => item.awakeable == awakeable,
+      );
+      if (index == -1) {
+        // we have already popped it; treat this as a 'done'
+        state.inFlight--;
+      } else {
+        // remove from the queue
+        state.items.splice(index, 1);
+      }
+
+      tick(ctx, state);
+
+      setState(ctx, state);
+    },
+  },
+});
+
+async function getState(ctx: ObjectContext<QueueState>): Promise<QueueState> {
+  return {
+    items: (await ctx.get("items")) ?? [],
+    inFlight: (await ctx.get("inFlight")) ?? 0,
+  };
+}
+
+function setState(ctx: ObjectContext<QueueState>, state: QueueState) {
+  ctx.set("items", state.items);
+  ctx.set("inFlight", state.inFlight);
+}
+
+function tick(ctx: ObjectContext<QueueState>, state: QueueState) {
+  while (state.inFlight < MAX_IN_FLIGHT && state.items.length > 0) {
+    let item = selectAndPopItem(state.items);
+    state.inFlight++;
+    ctx.resolveAwakeable(item.awakeable);
+  }
+
+  ctx.console.log(
+    `Tick end. Queue length: ${state.items.length}, In Flight: ${state.inFlight}`,
+  );
+}
+
+export type Queue = typeof queue;

patterns-use-cases/priority-queue/priority-queue-typescript/src/queue_client.ts

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+/*
+ * Copyright (c) 2024 - Restate Software, Inc., Restate GmbH
+ *
+ * This file is part of the Restate Examples for the Node.js/TypeScript SDK,
+ * which is released under the MIT license.
+ *
+ * You can find a copy of the license in the file LICENSE
+ * in the root directory of this repository or package or at
+ * https://github.com/restatedev/examples/blob/main/LICENSE
+ */
+
+import { Context, TerminalError } from "@restatedev/restate-sdk";
+import type { Queue as QueueObject } from "./queue";
+
+export interface Queue {
+  run<T>(priority: number, op: () => Promise<T>): Promise<T>;
+}
+
+export namespace Queue {
+  export function fromContext(ctx: Context, name: string): Queue {
+    return {
+      async run<T>(priority: number, op: () => Promise<T>): Promise<T> {
+        const client = ctx.objectSendClient<QueueObject>(
+          { name: "queue" },
+          name,
+        );
+
+        const awakeable = ctx.awakeable();
+        client.push({
+          awakeable: awakeable.id,
+          priority,
+        });
+
+        try {
+          await awakeable.promise;
+        } catch (e) {
+          if (e instanceof TerminalError) {
+            // this should only happen on cancellation; inform the queue that we no longer need to be scheduled
+            client.drop(awakeable.id);
+          }
+          throw e;
+        }
+
+        try {
+          const result = await op();
+
+          client.done();
+
+          return result;
+        } catch (e) {
+          if (e instanceof TerminalError) {
+            client.done();
+          }
+          throw e;
+        }
+      },
+    };
+  }
+}

patterns-use-cases/priority-queue/priority-queue-typescript/src/service.ts

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+/*
+ * Copyright (c) 2024 - Restate Software, Inc., Restate GmbH
+ *
+ * This file is part of the Restate Examples for the Node.js/TypeScript SDK,
+ * which is released under the MIT license.
+ *
+ * You can find a copy of the license in the file LICENSE
+ * in the root directory of this repository or package or at
+ * https://github.com/restatedev/examples/blob/main/LICENSE
+ */
+
+import { Context, service } from "@restatedev/restate-sdk";
+import { Queue } from "./queue_client";
+
+const QUEUE_NAME = "myService/expensiveMethod";
+
+export const myService = service({
+  name: "myService",
+  handlers: {
+    expensiveMethod: async (
+      ctx: Context,
+      params: { left: number; right: number; priority?: number },
+    ): Promise<number> => {
+      const queue = Queue.fromContext(ctx, QUEUE_NAME);
+      return queue.run(params.priority ?? 1, () =>
+        expensiveOperation(ctx, params.left, params.right),
+      );
+    },
+  },
+});
+
+async function expensiveOperation(
+  ctx: Context,
+  left: number,
+  right: number,
+): Promise<number> {
+  return ctx.run(async () => {
+    // very cpu heavy - important that the queue protects this
+    await new Promise((resolve) => setTimeout(resolve, 5_000));
+    return left + right;
+  });
+}
+
+export type MyService = typeof myService;

patterns-use-cases/priority-queue/priority-queue-typescript/tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "esnext",
+    "lib": ["esnext"],
+    "module": "nodenext",
+    "allowJs": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "outDir": "./dist",
+    "allowSyntheticDefaultImports": true,
+    "esModuleInterop": true,
+    "forceConsistentCasingInFileNames": true,
+    "strict": true,
+    "skipDefaultLibCheck": true,
+    "skipLibCheck": true
+  }
+}