Merge pull request #24339 from vespa-engine/havardpe/experiment-with-coroutines

experiment with coroutines

9 files changed, 218 insertions, 3 deletions

diff --git a/vespalib/CMakeLists.txt b/vespalib/CMakeLists.txt
index 8edd7fb2c5d..6ecac23d5fa 100644
--- a/vespalib/CMakeLists.txt
+++ b/vespalib/CMakeLists.txt
@@ -42,6 +42,8 @@ vespa_define_module(
     src/tests/component
     src/tests/compress
     src/tests/compression
+    src/tests/coro/detached
+    src/tests/coro/lazy
     src/tests/cpu_usage
     src/tests/crc
     src/tests/crypto
@@ -202,9 +204,13 @@ vespa_define_module(
     src/tests/fastlib/text
 
     LIBS
+    src/vespa/fastlib/io
+    src/vespa/fastlib/text
+    src/vespa/fastlib/text/apps
     src/vespa/vespalib
     src/vespa/vespalib/btree
     src/vespa/vespalib/component
+    src/vespa/vespalib/coro
     src/vespa/vespalib/crypto
     src/vespa/vespalib/data
     src/vespa/vespalib/data/slime
@@ -231,7 +237,4 @@ vespa_define_module(
     src/vespa/vespalib/time
     src/vespa/vespalib/trace
     src/vespa/vespalib/util
-    src/vespa/fastlib/io
-    src/vespa/fastlib/text
-    src/vespa/fastlib/text/apps
 )
diff --git a/vespalib/src/tests/coro/detached/CMakeLists.txt b/vespalib/src/tests/coro/detached/CMakeLists.txt
new file mode 100644
index 00000000000..237b8615fec
--- /dev/null
+++ b/vespalib/src/tests/coro/detached/CMakeLists.txt
@@ -0,0 +1,9 @@
+# Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+vespa_add_executable(vespalib_detached_test_app TEST
+    SOURCES
+    detached_test.cpp
+    DEPENDS
+    vespalib
+    GTest::GTest
+)
+vespa_add_test(NAME vespalib_detached_test_app COMMAND vespalib_detached_test_app)
diff --git a/vespalib/src/tests/coro/detached/detached_test.cpp b/vespalib/src/tests/coro/detached/detached_test.cpp
new file mode 100644
index 00000000000..f23d16cc75c
--- /dev/null
+++ b/vespalib/src/tests/coro/detached/detached_test.cpp
@@ -0,0 +1,19 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#include <vespa/vespalib/coro/detached.h>
+#include <vespa/vespalib/gtest/gtest.h>
+
+using vespalib::coro::Detached;
+
+Detached set_result(int &res, int value) {
+    res = value;
+    co_return;
+}
+
+TEST(DetachedTest, call_detached_coroutine) {
+    int result = 0;
+    set_result(result, 42);
+    EXPECT_EQ(result, 42);
+}
+
+GTEST_MAIN_RUN_ALL_TESTS()
diff --git a/vespalib/src/tests/coro/lazy/CMakeLists.txt b/vespalib/src/tests/coro/lazy/CMakeLists.txt
new file mode 100644
index 00000000000..daa11eb3576
--- /dev/null
+++ b/vespalib/src/tests/coro/lazy/CMakeLists.txt
@@ -0,0 +1,9 @@
+# Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+vespa_add_executable(vespalib_lazy_test_app TEST
+    SOURCES
+    lazy_test.cpp
+    DEPENDS
+    vespalib
+    GTest::GTest
+)
+vespa_add_test(NAME vespalib_lazy_test_app COMMAND vespalib_lazy_test_app)
diff --git a/vespalib/src/tests/coro/lazy/lazy_test.cpp b/vespalib/src/tests/coro/lazy/lazy_test.cpp
new file mode 100644
index 00000000000..a715e473aaf
--- /dev/null
+++ b/vespalib/src/tests/coro/lazy/lazy_test.cpp
@@ -0,0 +1,44 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#include <vespa/vespalib/coro/lazy.h>
+#include <vespa/vespalib/coro/sync_wait.h>
+#include <vespa/vespalib/gtest/gtest.h>
+
+using vespalib::coro::Lazy;
+using vespalib::coro::sync_wait;
+
+Lazy<int> make_lazy(int value) {
+    co_return value;
+}
+
+Lazy<int> async_add_values(int a, int b) {
+    auto lazy_a = make_lazy(a);
+    auto lazy_b = make_lazy(b);
+    co_return (co_await lazy_a + co_await lazy_b);
+}
+
+Lazy<int> async_sum(Lazy<int> a, Lazy<int> b) {
+    co_return (co_await a + co_await b);
+}
+
+TEST(LazyTest, simple_lazy_value) {
+    auto lazy = make_lazy(42);
+    auto result = sync_wait(lazy);
+    EXPECT_EQ(result, 42);
+}
+
+TEST(LazyTest, async_sum_of_async_values) {
+    auto lazy = async_add_values(10, 20);
+    auto result = sync_wait(lazy);
+    EXPECT_EQ(result, 30);
+}
+
+TEST(LazyTest, async_sum_of_external_async_values) {
+    auto a = make_lazy(100);
+    auto b = make_lazy(200);
+    auto lazy = async_sum(std::move(a), std::move(b));
+    auto result = sync_wait(lazy);
+    EXPECT_EQ(result, 300);
+}
+
+GTEST_MAIN_RUN_ALL_TESTS()
diff --git a/vespalib/src/vespa/vespalib/coro/CMakeLists.txt b/vespalib/src/vespa/vespalib/coro/CMakeLists.txt
new file mode 100644
index 00000000000..d190c2e8ddc
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/coro/CMakeLists.txt
@@ -0,0 +1,5 @@
+# Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+vespa_add_library(vespalib_vespalib_coro OBJECT
+    SOURCES
+    DEPENDS
+)
diff --git a/vespalib/src/vespa/vespalib/coro/detached.h b/vespalib/src/vespa/vespalib/coro/detached.h
new file mode 100644
index 00000000000..6d051e53121
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/coro/detached.h
@@ -0,0 +1,20 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include <coroutine>
+#include <exception>
+
+namespace vespalib::coro {
+
+struct Detached {
+    struct promise_type {
+        Detached get_return_object() { return {}; }
+        static std::suspend_never initial_suspend() noexcept { return {}; }
+        static std::suspend_never final_suspend() noexcept { return {}; }
+        static void unhandled_exception() { std::terminate(); }
+        void return_void() noexcept {};
+    };
+};
+
+}
diff --git a/vespalib/src/vespa/vespalib/coro/lazy.h b/vespalib/src/vespa/vespalib/coro/lazy.h
new file mode 100644
index 00000000000..b007f565c93
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/coro/lazy.h
@@ -0,0 +1,72 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include <concepts>
+#include <coroutine>
+#include <optional>
+
+namespace vespalib::coro {
+
+template <std::movable T>
+class [[nodiscard]] Lazy {
+public:
+    struct promise_type {
+        Lazy<T> get_return_object() { return Lazy(Handle::from_promise(*this)); }
+        static std::suspend_always initial_suspend() noexcept { return {}; }
+        static auto final_suspend() noexcept {
+            struct awaiter {
+                bool await_ready() const noexcept { return false; }
+                std::coroutine_handle<> await_suspend(Handle handle) const noexcept {
+                    auto waiter = handle.promise().waiter;
+                    return waiter ? waiter : std::noop_coroutine();
+                }
+                void await_resume() const noexcept {}
+            };
+            return awaiter();
+        }
+        void return_value(T ret_value) noexcept {
+            value = std::move(ret_value);
+        }
+        static void unhandled_exception() { std::terminate(); }
+        std::optional<T> value;
+        std::coroutine_handle<> waiter;
+        promise_type(promise_type &&) = delete;
+        promise_type(const promise_type &) = delete;
+        promise_type() : value(std::nullopt), waiter(nullptr) {}
+    };
+    using Handle = std::coroutine_handle<promise_type>;
+
+private:
+    Handle _handle;
+
+public:
+    Lazy(const Lazy &) = delete;
+    Lazy &operator=(const Lazy &) = delete;
+    explicit Lazy(Handle handle_in) noexcept : _handle(handle_in) {}
+    Lazy(Lazy &&rhs) noexcept : _handle(std::exchange(rhs._handle, nullptr)) {}
+    auto operator co_await() {
+        struct awaiter {
+            Handle handle;
+            bool await_ready() const noexcept {
+                return handle.done();
+            }
+            Handle await_suspend(std::coroutine_handle<> waiter) const noexcept {
+                handle.promise().waiter = waiter;
+                return handle;
+            }
+            T &await_resume() const noexcept {
+                return *handle.promise().value;
+            }
+            awaiter(Handle handle_in) : handle(handle_in) {}
+        };
+        return awaiter(_handle);
+    }
+    ~Lazy() {
+        if (_handle) {
+            _handle.destroy();
+        }
+    }
+};
+
+}
diff --git a/vespalib/src/vespa/vespalib/coro/sync_wait.h b/vespalib/src/vespa/vespalib/coro/sync_wait.h
new file mode 100644
index 00000000000..e6a8fdc43f6
--- /dev/null
+++ b/vespalib/src/vespa/vespalib/coro/sync_wait.h
@@ -0,0 +1,34 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#pragma once
+
+#include "detached.h"
+#include "lazy.h"
+#include <coroutine>
+#include <vespa/vespalib/util/gate.h>
+
+namespace vespalib::coro {
+
+template <typename T, typename S>
+Detached signal_when_done(Lazy<T> &value, S &sink) {
+    sink(co_await value);
+}
+
+template <typename T>
+T &sync_wait(Lazy<T> &value) {
+    struct MySink {
+        Gate gate;
+        T *result;
+        void operator()(T &result_in) {
+            result = &result_in;
+            gate.countDown();
+        }
+        MySink() : gate(), result(nullptr) {}
+    };
+    MySink sink;
+    signal_when_done(value, sink);
+    sink.gate.await();
+    return *sink.result;
+}
+
+}