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node_modules/sequelize/lib/dialects/mssql/resource-lock.js

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+'use strict';
+
+const Promise = require('../../promise');
+
+class ResourceLock {
+  constructor(resource) {
+    this.resource = resource;
+    this.previous = Promise.resolve(resource);
+  }
+
+  unwrap() {
+    return this.resource;
+  }
+
+  lock() {
+    const lock = this.previous;
+    let resolve;
+    this.previous = new Promise(r => {
+      resolve = r;
+    });
+    return lock.disposer(resolve);
+  }
+}
+
+module.exports = ResourceLock;