SERVER-46514 Allow mirroring maestro to leave GC for the client thread

1 files changed, 171 insertions, 0 deletions

diff --git a/src/mongo/db/client_out_of_line_executor_test.cpp b/src/mongo/db/client_out_of_line_executor_test.cpp
new file mode 100644
index 00000000000..cffeb633c87
--- /dev/null
+++ b/src/mongo/db/client_out_of_line_executor_test.cpp
@@ -0,0 +1,171 @@
+/**
+ *    Copyright (C) 2020-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 <memory>
+
+#include "mongo/db/client.h"
+#include "mongo/db/client_out_of_line_executor.h"
+#include "mongo/db/service_context.h"
+#include "mongo/platform/atomic_word.h"
+#include "mongo/stdx/thread.h"
+#include "mongo/unittest/barrier.h"
+#include "mongo/unittest/unittest.h"
+
+namespace mongo {
+namespace {
+
+/**
+ * The following implements a pseudo garbage collector to test client's out-of-line executor.
+ */
+class ClientOutOfLineExecutorTest : public unittest::Test {
+public:
+    class DummyInstance {
+    public:
+        DummyInstance() = delete;
+
+        DummyInstance(ClientOutOfLineExecutorTest* parent) : _parent(parent) {
+            _parent->_instanceCount.fetchAndAdd(1);
+        }
+
+        DummyInstance(DummyInstance&& other) : _parent(std::move(other._parent)) {
+            _parent->_instanceCount.fetchAndAdd(1);
+        }
+
+        DummyInstance(const DummyInstance& other) {
+            MONGO_UNREACHABLE;
+        }
+
+        ~DummyInstance() {
+            _parent->_instanceCount.fetchAndAdd(-1);
+        }
+
+    private:
+        ClientOutOfLineExecutorTest* _parent;
+    };
+
+    void setUp() override {
+        setGlobalServiceContext(ServiceContext::make());
+        Client::initThread(kClientThreadName);
+        _instanceCount.store(0);
+    }
+
+    void tearDown() override {
+        auto client = Client::releaseCurrent();
+        client.reset(nullptr);
+    }
+
+    auto getDecoration() noexcept {
+        return ClientOutOfLineExecutor::get(Client::getCurrent());
+    }
+
+    int countDummies() const noexcept {
+        return _instanceCount.load();
+    }
+
+    static constexpr auto kClientThreadName = "ClientOutOfLineExecutorTest"_sd;
+
+private:
+    friend class DummyInstance;
+
+    AtomicWord<int> _instanceCount;
+};
+
+TEST_F(ClientOutOfLineExecutorTest, CheckDecoration) {
+    auto decoration = getDecoration();
+    ASSERT(decoration);
+}
+
+TEST_F(ClientOutOfLineExecutorTest, ScheduleAndExecute) {
+    auto thread = stdx::thread([this, handle = getDecoration()->getHandle()]() mutable {
+        DummyInstance dummy(this);
+        handle.schedule([dummy = std::move(dummy)](const Status& status) {
+            ASSERT_OK(status);
+            ASSERT_EQ(getThreadName(), ClientOutOfLineExecutorTest::kClientThreadName);
+        });
+    });
+    thread.join();
+    ASSERT_EQ(countDummies(), 1);
+
+    getDecoration()->consumeAllTasks();
+    ASSERT_EQ(countDummies(), 0);
+}
+
+TEST_F(ClientOutOfLineExecutorTest, DestructorExecutesLeftovers) {
+    const auto kDummiesCount = 8;
+    unittest::Barrier b1(2), b2(2);
+
+    auto thread = stdx::thread([this, kDummiesCount, b1 = &b1, b2 = &b2]() {
+        Client::initThread("ThreadWithLeftovers"_sd);
+
+        auto handle = ClientOutOfLineExecutor::get(Client::getCurrent())->getHandle();
+        for (auto i = 0; i < kDummiesCount; i++) {
+            DummyInstance dummy(this);
+            handle.schedule([dummy = std::move(dummy),
+                             threadId = stdx::this_thread::get_id()](const Status& status) {
+                ASSERT(status == ErrorCodes::ClientDisconnect);
+                // Avoid using `getThreadName()` here as it'll cause read-after-delete errors.
+                ASSERT_EQ(threadId, stdx::this_thread::get_id());
+            });
+        }
+
+        b1->countDownAndWait();
+        // Wait for the main thread to count dummies.
+        b2->countDownAndWait();
+    });
+
+    b1.countDownAndWait();
+    ASSERT_EQ(countDummies(), kDummiesCount);
+    b2.countDownAndWait();
+
+    thread.join();
+    ASSERT_EQ(countDummies(), 0);
+}
+
+TEST_F(ClientOutOfLineExecutorTest, ScheduleAfterClientThreadReturns) {
+    ClientOutOfLineExecutor::QueueHandle handle;
+
+    auto thread = stdx::thread([&handle]() mutable {
+        Client::initThread("ClientThread"_sd);
+        handle = ClientOutOfLineExecutor::get(Client::getCurrent())->getHandle();
+        // Return to destroy the client, and close the task queue.
+    });
+
+    thread.join();
+
+    bool taskCalled = false;
+    handle.schedule([&taskCalled, threadName = getThreadName()](const Status& status) {
+        ASSERT(status == ErrorCodes::CallbackCanceled);
+        ASSERT_EQ(getThreadName(), threadName);
+        taskCalled = true;
+    });
+    ASSERT(taskCalled);
+}
+
+}  // namespace
+}  // namespace mongo