1 files changed, 21 insertions, 0 deletions

diff --git a/server/helpers/promise-cache.ts b/server/helpers/promise-cache.ts
new file mode 100644
index 000000000..07e8a9962
--- /dev/null
+++ b/server/helpers/promise-cache.ts
@@ -0,0 +1,21 @@
+export class PromiseCache <A, R> {
+  private readonly running = new Map<string, Promise<R>>()
+
+  constructor (
+    private readonly fn: (arg: A) => Promise<R>,
+    private readonly keyBuilder: (arg: A) => string
+  ) {
+  }
+
+  run (arg: A) {
+    const key = this.keyBuilder(arg)
+
+    if (this.running.has(key)) return this.running.get(key)
+
+    const p = this.fn(arg)
+
+    this.running.set(key, p)
+
+    return p.finally(() => this.running.delete(key))
+  }
+}