SERVER-62560 implement valid() on Future types

4 files changed, 320 insertions, 0 deletions

diff --git a/src/mongo/util/SConscript b/src/mongo/util/SConscript
index aa7d3e07231..127160cd253 100644
--- a/src/mongo/util/SConscript
+++ b/src/mongo/util/SConscript
@@ -691,6 +691,7 @@ icuEnv.CppUnitTest(
         'future_test_future_int.cpp',
         'future_test_future_move_only.cpp',
         'future_test_future_void.cpp',
+        'future_test_valid.cpp',
         'future_test_promise_int.cpp',
         'future_test_promise_void.cpp',
         'future_test_shared_future.cpp',
diff --git a/src/mongo/util/future.h b/src/mongo/util/future.h
index 5d36bb39861..cfdb724a101 100644
--- a/src/mongo/util/future.h
+++ b/src/mongo/util/future.h
@@ -181,6 +181,16 @@ public:
     }
 
     /**
+     * Returns whether this SemiFuture can or will be able to access a deferred status or value.
+     *
+     * NOTE: valid() will still return true if the value inside of the future is moved from. This
+     * should not be used as a way to determine usage validity until SERVER-66036.
+     */
+    bool valid() const {
+        return _impl.valid();
+    }
+
+    /**
      * Returns when the Semifuture isReady().
      *
      * Throws if the interruptible passed is interrupted (explicitly or via deadline).
@@ -316,6 +326,7 @@ public:
     using SemiFuture<T>::SemiFuture;  // Constructors.
     using SemiFuture<T>::share;
     using SemiFuture<T>::isReady;
+    using SemiFuture<T>::valid;
     using SemiFuture<T>::wait;
     using SemiFuture<T>::waitNoThrow;
     using SemiFuture<T>::get;
@@ -594,6 +605,7 @@ public:
     using value_type = T;
     using SemiFuture<T>::share;
     using SemiFuture<T>::isReady;
+    using SemiFuture<T>::valid;
     using SemiFuture<T>::wait;
     using SemiFuture<T>::waitNoThrow;
     using SemiFuture<T>::get;
@@ -970,6 +982,10 @@ public:
         return _shared.isReady();
     }
 
+    bool valid() const {
+        return _shared.valid();
+    }
+
     void wait(Interruptible* interruptible = Interruptible::notInterruptible()) const {
         _shared.wait(interruptible);
     }
diff --git a/src/mongo/util/future_impl.h b/src/mongo/util/future_impl.h
index 6fe25a51fb5..b1ef0ffd955 100644
--- a/src/mongo/util/future_impl.h
+++ b/src/mongo/util/future_impl.h
@@ -654,6 +654,10 @@ public:
         return _shared->state.load(std::memory_order_acquire) == SSBState::kFinished;
     }
 
+    bool valid() const {
+        return _shared != nullptr;
+    }
+
     void wait(Interruptible* interruptible) const {
         _shared->wait(interruptible);
     }
@@ -757,6 +761,10 @@ public:
         return _inner.isReady();
     }
 
+    bool valid() const {
+        return _inner.valid();
+    }
+
     void wait(Interruptible* interruptible) const {
         _inner.wait(interruptible);
     }
@@ -824,6 +832,16 @@ public:
         return _immediate || _shared.isReady();
     }
 
+    /**
+     * Returns whether the Future has or can eventually have access to a deferred value or status.
+     *
+     * NOTE: this does not return whether that deferred value is itself valid. It could have been
+     * moved from.
+     */
+    bool valid() const {
+        return _immediate || _shared.valid();
+    }
+
     void wait(Interruptible* interruptible) const {
         if (_immediate)
             return;
diff --git a/src/mongo/util/future_test_valid.cpp b/src/mongo/util/future_test_valid.cpp
new file mode 100644
index 00000000000..2ca85a19f26
--- /dev/null
+++ b/src/mongo/util/future_test_valid.cpp
@@ -0,0 +1,285 @@
+/**
+ *    Copyright (C) 2022-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    This program is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#include "mongo/util/future.h"
+
+#include "mongo/stdx/thread.h"
+#include "mongo/unittest/death_test.h"
+#include "mongo/unittest/unittest.h"
+#include "mongo/util/future_test_utils.h"
+
+#include <boost/optional.hpp>
+
+namespace mongo {
+namespace {
+
+/**
+ * TODO(SERVER-66036): Expand testing to ensure that `valid()` semantics are in line with "valid
+ * usage" semantics.
+ */
+
+/**
+ * These tests validate the postconditions of operations on the 4 future types:
+ * - Future
+ * - SemiFuture
+ * - SharedSemiFuture
+ * - ExecutorFuture
+ *
+ * TODO(SERVER-66036): use FUTURE_SUCCESS_TEST in all helpers for better coverage of ExecutorFuture.
+ */
+
+/** Asserts that the Future is still valid() after `func`. */
+template <typename TestFunc>
+void assertFutureValidAfter(const TestFunc& func) {
+    FUTURE_SUCCESS_TEST([] { return 0; },
+                        [func](auto&& fut) {
+                            func(std::move(fut));
+                            ASSERT_TRUE(fut.valid());
+                        });
+}
+
+/** Asserts that `func` returns a valid() future while making the input Future non-valid(). */
+template <DoExecutorFuture doExecutorFuture = kDoExecutorFuture, typename TestFunc>
+void assertFutureTransfersValid(const TestFunc& func) {
+    // TODO(SERVER-66036): use FUTURE_SUCCESS_TEST once moves from _immediate have the same
+    // semantics as moves from SharedState
+    auto [promise, fut] = makePromiseFuture<int>();
+    promise.emplaceValue(0);
+    auto otherFut = func(std::move(fut));
+    ASSERT_FALSE(fut.valid());  // NOLINT
+    ASSERT_TRUE(otherFut.valid());
+}
+
+TEST(FutureValid, ValidAtStart) {
+    FUTURE_SUCCESS_TEST([] { return 0; }, [](auto&& fut) { ASSERT_TRUE(fut.valid()); });
+}
+
+// TODO SERVER-64948: this test is only needed if the lvalue& getter is kept around.
+TEST(FutureValid, ValidAfterGetLvalue) {
+    assertFutureValidAfter([](auto&& fut) { [[maybe_unused]] auto val = fut.get(); });
+}
+
+TEST(FutureValid, ValidAfterGetConstLvalue) {
+    assertFutureValidAfter([](const auto& fut) { [[maybe_unused]] auto val = fut.get(); });
+}
+
+TEST(FutureValid, ValidAfterGetNoThrowConstLvalue) {
+    assertFutureValidAfter([](const auto& fut) { [[maybe_unused]] auto val = fut.getNoThrow(); });
+}
+
+TEST(FutureValid, ValidAfterWait) {
+    assertFutureValidAfter([](auto&& fut) { fut.wait(); });
+}
+
+TEST(FutureValid, ValidAfterWaitNoThrow) {
+    assertFutureValidAfter([](auto&& fut) { [[maybe_unused]] auto status = fut.waitNoThrow(); });
+}
+
+TEST(FutureValid, ThenRunOnTransfersValid) {
+    assertFutureTransfersValid([](auto&& fut) {
+        auto exec = InlineQueuedCountingExecutor::make();
+        return std::move(fut).thenRunOn(exec);
+    });
+}
+
+TEST(FutureValid, MoveTransfersValid) {
+    assertFutureTransfersValid([](auto&& fut) { return std::move(fut); });
+}
+
+TEST(FutureValid, SemiTransfersValid) {
+    assertFutureTransfersValid([](auto&& fut) { return std::move(fut).semi(); });
+}
+
+TEST(FutureValid, ShareTransfersValid) {
+    assertFutureTransfersValid([](auto&& fut) { return std::move(fut).share(); });
+}
+
+/** Asserts that the SemiFuture is still valid() after `func`. */
+template <typename TestFunc>
+void assertSemiFutureValidAfter(const TestFunc& func) {
+    FUTURE_SUCCESS_TEST([] { return 0; },
+                        [func](auto&& fut) {
+                            auto semiFut = std::move(fut).semi();
+                            func(std::move(semiFut));
+                            ASSERT_TRUE(semiFut.valid());
+                        });
+}
+
+/* Asserts that `func` returns a valid() future while making the input SemiFuture non-valid(). */
+template <typename TestFunc>
+void assertSemiFutureTransfersValid(const TestFunc& func) {
+    // TODO(SERVER-66036): use FUTURE_SUCCESS_TEST once moves from _immediate have the same
+    // semantics as moves from SharedState
+    auto [promise, fut] = makePromiseFuture<int>();
+    promise.emplaceValue(0);
+    auto semiFut = std::move(fut).semi();
+    auto otherFut = func(std::move(semiFut));
+    ASSERT_FALSE(semiFut.valid());  // NOLINT
+    ASSERT_TRUE(otherFut.valid());
+}
+
+// TODO SERVER-64948: this test is only needed if the lvalue& getter is kept around.
+TEST(SemiFutureValid, ValidAfterGetLvalue) {
+    assertSemiFutureValidAfter([](auto&& fut) { [[maybe_unused]] auto val = fut.get(); });
+}
+
+TEST(SemiFutureValid, ValidAfterGetConstLvalue) {
+    assertSemiFutureValidAfter([](const auto& fut) { [[maybe_unused]] auto val = fut.get(); });
+}
+
+TEST(SemiFutureValid, ValidAfterGetNoThrowConstLvalue) {
+    assertSemiFutureValidAfter(
+        [](const auto& fut) { [[maybe_unused]] auto val = fut.getNoThrow(); });
+}
+
+TEST(SemiFutureValid, ValidAfterWait) {
+    assertSemiFutureValidAfter([](auto&& fut) { fut.wait(); });
+}
+
+TEST(SemiFutureValid, ValidAfterWaitNoThrow) {
+    assertSemiFutureValidAfter(
+        [](auto&& fut) { [[maybe_unused]] auto status = fut.waitNoThrow(); });
+}
+
+TEST(SemiFutureValid, ThenRunOnTransfersValid) {
+    assertSemiFutureTransfersValid([](auto&& fut) {
+        auto exec = InlineQueuedCountingExecutor::make();
+        return std::move(fut).thenRunOn(exec);
+    });
+}
+
+TEST(SemiFutureValid, MoveTransfersValid) {
+    assertSemiFutureTransfersValid([](auto&& fut) { return std::move(fut); });
+}
+
+TEST(SemiFutureValid, SemiTransfersValid) {
+    assertSemiFutureTransfersValid([](auto&& fut) { return std::move(fut).semi(); });
+}
+
+TEST(SemiFutureValid, ShareTransfersValid) {
+    assertSemiFutureTransfersValid([](auto&& fut) { return std::move(fut).share(); });
+}
+
+TEST(SemiFutureValid, UnsafeToInlineFutureTransfersValid) {
+    assertSemiFutureTransfersValid(
+        [](auto&& fut) { return std::move(fut).unsafeToInlineFuture(); });
+}
+
+/** Asserts that the SharedSemiFuture is still valid() after `func`. */
+template <typename TestFunc>
+void assertSharedSemiFutureValidAfter(const TestFunc& func) {
+    FUTURE_SUCCESS_TEST([] { return 0; },
+                        [func](auto&& fut) {
+                            auto sharedFut = std::move(fut).share();
+                            func(std::move(sharedFut));
+                            ASSERT_TRUE(sharedFut.valid());
+                        });
+}
+
+/**
+ * Asserts that `func` returns a valid() future while making the input SharedSemiFuture non-valid().
+ */
+template <typename TestFunc>
+void assertSharedSemiFutureTransfersValid(const TestFunc& func) {
+    // TODO(SERVER-66036): use FUTURE_SUCCESS_TEST once moves from _immediate have the same
+    // semantics as moves from SharedState
+    auto [promise, fut] = makePromiseFuture<int>();
+    promise.emplaceValue(0);
+    auto sharedFut = std::move(fut).share();
+    auto otherFut = func(std::move(sharedFut));
+    ASSERT_FALSE(sharedFut.valid());  // NOLINT
+    ASSERT_TRUE(otherFut.valid());
+}
+
+/** Asserts that `func` returns a valid() Future and keeps the input SharedSemiFuture valid(). */
+template <typename TestFunc>
+void assertSharedSemiFutureSplits(const TestFunc& func) {
+    // TODO(SERVER-66036): use FUTURE_SUCCESS_TEST once moves from _immediate have the same
+    // semantics as moves from SharedState
+    auto [promise, fut] = makePromiseFuture<int>();
+    promise.emplaceValue(0);
+    auto sharedFut = std::move(fut).share();
+    auto otherFut = func(std::move(sharedFut));
+    ASSERT_TRUE(sharedFut.valid());  // NOLINT
+    ASSERT_TRUE(otherFut.valid());
+}
+
+TEST(SharedSemiFutureValid, ValidAfterGetLvalue) {
+    assertSharedSemiFutureValidAfter([](auto&& fut) { [[maybe_unused]] auto val = fut.get(); });
+}
+
+TEST(SharedSemiFutureValid, ValidAfterGetConstLvalue) {
+    assertSharedSemiFutureValidAfter(
+        [](const auto& fut) { [[maybe_unused]] auto val = fut.get(); });
+}
+
+TEST(SharedSemiFutureValid, ValidAfterGetNoThrowLvalue) {
+    assertSharedSemiFutureValidAfter(
+        [](auto&& fut) { [[maybe_unused]] auto val = fut.getNoThrow(); });
+}
+
+TEST(SharedSemiFutureValid, ValidAfterGetNoThrowConstLvalue) {
+    assertSharedSemiFutureValidAfter(
+        [](const auto& fut) { [[maybe_unused]] auto val = fut.getNoThrow(); });
+}
+
+TEST(SharedSemiFutureValid, ValidAfterWait) {
+    assertSharedSemiFutureValidAfter([](auto&& fut) { fut.wait(); });
+}
+
+TEST(SharedSemiFutureValid, ValidAfterWaitNoThrow) {
+    assertSharedSemiFutureValidAfter(
+        [](auto&& fut) { [[maybe_unused]] auto status = fut.waitNoThrow(); });
+}
+
+TEST(SharedSemiFutureValid, ValidAfterThenRunOn) {
+    assertSharedSemiFutureSplits([](auto&& fut) {
+        auto exec = InlineQueuedCountingExecutor::make();
+        return fut.thenRunOn(exec);
+    });
+}
+
+TEST(SharedSemiFutureValid, MoveTransfersValid) {
+    assertSharedSemiFutureTransfersValid([](auto&& fut) { return std::move(fut); });
+}
+
+TEST(SharedSemiFutureValid, SemiRetainsValid) {
+    assertSharedSemiFutureSplits([](auto&& fut) { return std::move(fut).semi(); });
+}
+
+TEST(SharedSemiFutureValid, SplitRetainsValid) {
+    assertSharedSemiFutureSplits([](auto&& fut) { return std::move(fut).split(); });
+}
+
+TEST(SharedSemiFutureValid, UnsafeToInlineFutureRetainsValid) {
+    assertSharedSemiFutureSplits([](auto&& fut) { return std::move(fut).unsafeToInlineFuture(); });
+}
+
+}  // namespace
+}  // namespace mongo