1 files changed, 42 insertions, 0 deletions
diff --git a/vespalib/src/vespa/vespalib/coro/active_work.h b/vespalib/src/vespa/vespalib/coro/active_work.h
new file mode 100644
index 00000000000..9f4079615c7
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/coro/active_work.h
@@ -0,0 +1,42 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include "lazy.h"
+#include "detached.h"
+#include <coroutine>
+#include <atomic>
+
+namespace vespalib::coro {
+
+// Tracks work that is being performed concurrently
+class ActiveWork {
+private:
+    std::atomic<uint32_t> _pending;
+    std::coroutine_handle<> _waiting;
+    template <typename T>
+    Detached signal_when_done(Lazy<T> &lazy) {
+        co_await lazy.done();
+        if (_pending.fetch_sub(1, std::memory_order_acq_rel) == 1) {
+            _waiting.resume();
+        }
+    }
+    struct join_awaiter {
+        ActiveWork &self;
+        join_awaiter(ActiveWork &self_in) noexcept : self(self_in) {}
+        constexpr bool await_ready() const noexcept { return false; }
+        constexpr void await_resume() const noexcept {}
+        bool await_suspend(std::coroutine_handle<> handle) noexcept __attribute__((noinline));
+    };
+public:
+    ActiveWork() : _pending(1), _waiting(std::noop_coroutine()) {}
+    ~ActiveWork();
+    template <typename T>
+    void start(Lazy<T> &lazy) {
+        _pending.fetch_add(1, std::memory_order_relaxed);
+        signal_when_done(lazy);
+    }
+    auto join() noexcept { return join_awaiter(*this); }
+};
+
+}