Merge branch 'main' of git.sr.ht:~jacqueline/tangara-fw

1 files changed, 62 insertions, 0 deletions

diff --git a/src/database/include/future_fetcher.hpp b/src/database/include/future_fetcher.hpp
new file mode 100644
index 00000000..e8ce9729
--- /dev/null
+++ b/src/database/include/future_fetcher.hpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright 2023 jacqueline <me@jacqueline.id.au>
+ *
+ * SPDX-License-Identifier: GPL-3.0-only
+ */
+
+#pragma once
+
+#include <memory>
+#include <utility>
+
+#include "database.hpp"
+
+namespace database {
+
+/*
+ * Utility to simplify waiting for a std::future to complete without blocking.
+ * Each instance is good for a single future, and does not directly own anything
+ * other than the future itself.
+ */
+template <typename T>
+class FutureFetcher {
+ public:
+  explicit FutureFetcher(std::future<T>&& fut)
+      : is_consumed_(false), fut_(std::move(fut)) {}
+
+  /*
+   * Returns whether or not the underlying future is still awaiting async work.
+   */
+  auto Finished() -> bool {
+    if (!fut_.valid()) {
+      return true;
+    }
+    if (fut_.wait_for(std::chrono::seconds(0)) != std::future_status::ready) {
+      return false;
+    }
+    return true;
+  }
+
+  /*
+   * Returns the result of the future, and releases ownership of the underling
+   * resource. Will return an absent value if the future became invalid (e.g.
+   * the promise associated with it was destroyed.)
+   */
+  auto Result() -> std::optional<T> {
+    assert(!is_consumed_);
+    if (is_consumed_) {
+      return {};
+    }
+    is_consumed_ = true;
+    if (!fut_.valid()) {
+      return {};
+    }
+    return fut_.get();
+  }
+
+ private:
+  bool is_consumed_;
+  std::future<T> fut_;
+};
+
+}  // namespace database