Move locks to their own DB collection

lib/lock.ts

@@ -0,0 +1,45 @@
+import { collections } from "./db/db";
+
+const CLOCK_SKEW_TOLERANCE = 30000;
+
+export async function acquireLock(
+  lockName: string,
+  ttl: number,
+  timeout = 0,
+  token = Math.random().toString(36).slice(2)
+): Promise<string> {
+  try {
+    const now = Date.now();
+    const r = await collections.locks.findOneAndUpdate(
+      { _id: lockName, value: token },
+      {
+        $set: {
+          expire: new Date(now + ttl + CLOCK_SKEW_TOLERANCE),
+        },
+        $currentDate: { timestamp: true },
+      },
+      { upsert: true, returnDocument: "after" }
+    );
+    if (Math.abs(r.value.timestamp.getTime() - now) > CLOCK_SKEW_TOLERANCE)
+      throw new Error("Database clock skew too great");
+  } catch (err) {
+    if (err.code !== 11000) throw err;
+    if (!(timeout > 0)) return null;
+    const w = 50 + Math.random() * 50;
+    await new Promise((resolve) => setTimeout(resolve, w));
+    return acquireLock(lockName, ttl, timeout - w, token);
+  }
+
+  return token;
+}
+
+export async function releaseLock(
+  lockName: string,
+  token: string
+): Promise<void> {
+  const res = await collections.locks.deleteOne({
+    _id: lockName,
+    value: token,
+  });
+  if (res.deletedCount !== 1) throw new Error("Lock expired");
+}