阶段2（上）：后端专题 Go/Gin/PostgreSQL/MySQL/Redis/MQ/gRPC 的课程、企业场景、面试题和可运行示例

topics/backend/mq/examples/delay-cancel/delay_cancel.py

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+# requires: aio_pika
+"""RabbitMQ 延迟取消订单：消息先进带 TTL 的等待队列，过期后经死信交换机转到处理队列。
+
+运行：AMQP_URL=amqp://guest:guest@localhost/ python delay_cancel.py
+没有设置 AMQP_URL 时打印提示并正常退出。会创建并删除名字带随机后缀的交换机和队列。
+"""
+import asyncio
+import json
+import os
+import sys
+import time
+import uuid
+
+import aio_pika
+
+DELAY_MS = 1000  # 演示用 1 秒；真实业务常见是 15~30 分钟
+
+
+class OrderStore:
+    """模拟数据库里的订单状态（真实项目里用条件 UPDATE 保证幂等）。"""
+
+    def __init__(self) -> None:
+        self.status: dict[str, str] = {}
+
+    def cancel_if_unpaid(self, order_id: str) -> bool:
+        # 等价于 UPDATE orders SET status='cancelled' WHERE id=? AND status='pending'
+        if self.status.get(order_id) == "pending":
+            self.status[order_id] = "cancelled"
+            return True
+        return False
+
+
+async def main() -> int:
+    url = os.environ.get("AMQP_URL")
+    if not url:
+        print("未设置 AMQP_URL，跳过（示例：amqp://guest:guest@localhost/）")
+        return 0
+    suffix = uuid.uuid4().hex[:8]
+    conn = await aio_pika.connect_robust(url)
+    async with conn:
+        ch = await conn.channel()
+        await ch.set_qos(prefetch_count=10)
+        dlx = await ch.declare_exchange(f"order.dlx.{suffix}", aio_pika.ExchangeType.DIRECT, auto_delete=True)
+        # 处理队列：真正执行“超时取消”的消费者监听这里
+        work_q = await ch.declare_queue(f"order.cancel.{suffix}", durable=True, auto_delete=True)
+        await work_q.bind(dlx, routing_key="cancel")
+        # 等待队列：没有消费者，消息在这里过期后转到死信交换机
+        wait_q = await ch.declare_queue(f"order.wait.{suffix}", durable=True, auto_delete=True, arguments={
+            "x-message-ttl": DELAY_MS,
+            "x-dead-letter-exchange": dlx.name,
+            "x-dead-letter-routing-key": "cancel",
+        })
+
+        store = OrderStore()
+        store.status = {"o1": "pending", "o2": "pending"}
+        start = time.monotonic()
+        for oid in ("o1", "o2", "o1"):  # o1 故意发两次，模拟重复消息
+            await ch.default_exchange.publish(
+                aio_pika.Message(json.dumps({"order_id": oid}).encode(),
+                                 delivery_mode=aio_pika.DeliveryMode.PERSISTENT, message_id=f"cancel-{oid}"),
+                routing_key=wait_q.name)
+        store.status["o2"] = "paid"  # o2 在超时前支付了
+
+        results: list[tuple[str, bool]] = []
+        async with work_q.iterator() as it:
+            async for msg in it:
+                async with msg.process():  # 正常结束自动 ack，抛异常则 nack
+                    oid = json.loads(msg.body)["order_id"]
+                    results.append((oid, store.cancel_if_unpaid(oid)))
+                if len(results) == 3:
+                    break
+        elapsed = time.monotonic() - start
+        print("处理结果：", results, f"耗时 {elapsed:.1f}s")
+        assert elapsed >= DELAY_MS / 1000 * 0.9, "消息应该在延迟之后才被处理"
+        assert store.status == {"o1": "cancelled", "o2": "paid"}, store.status
+        assert sorted(results) == [("o1", False), ("o1", True), ("o2", False)]  # 重复消息不会重复取消
+        await wait_q.delete(if_unused=False, if_empty=False)
+        await work_q.delete(if_unused=False, if_empty=False)
+        print("延迟取消正确：未支付的被取消，已支付的不受影响，重复消息幂等")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(asyncio.run(main()))