SERVER-49108 Convert buildInfo command to async implementation

3 files changed, 174 insertions, 0 deletions

diff --git a/src/mongo/executor/SConscript b/src/mongo/executor/SConscript
index 2cb463484bd..de5ad45d9eb 100644
--- a/src/mongo/executor/SConscript
+++ b/src/mongo/executor/SConscript
@@ -280,6 +280,19 @@ env.Library(
     ],
 )
 
+env.Library(
+    target='async_request_executor',
+    source=[
+        'async_request_executor.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+        '$BUILD_DIR/mongo/db/service_context',
+        '$BUILD_DIR/mongo/util/concurrency/thread_pool',
+        '$BUILD_DIR/mongo/util/fail_point',
+    ],
+)
+
 env.CppUnitTest(
     target='executor_test',
     source=[
diff --git a/src/mongo/executor/async_request_executor.cpp b/src/mongo/executor/async_request_executor.cpp
new file mode 100644
index 00000000000..cf535e864f6
--- /dev/null
+++ b/src/mongo/executor/async_request_executor.cpp
@@ -0,0 +1,88 @@
+/**
+ *    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.
+ */
+
+#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kExecutor
+
+#include "mongo/executor/async_request_executor.h"
+
+#include "mongo/db/client_strand.h"
+#include "mongo/db/operation_context.h"
+#include "mongo/logv2/log.h"
+#include "mongo/platform/compiler.h"
+#include "mongo/util/fail_point.h"
+
+namespace mongo {
+
+MONGO_FAIL_POINT_DEFINE(hangBeforeRunningAsyncRequestExecutorTask);
+
+AsyncRequestExecutor::AsyncRequestExecutor(std::string name) : _name(std::move(name)) {
+    ThreadPool::Options options;
+    options.minThreads = 0;
+    options.maxThreads = 1;
+    _pool = std::make_unique<ThreadPool>(std::move(options));
+    _pool->startup();
+    LOGV2_DEBUG(
+        4910801, kDiagnosticLogLevel, "Started asynchronous request executor", "name"_attr = _name);
+}
+
+AsyncRequestExecutor::~AsyncRequestExecutor() {
+    _pool->shutdown();
+    _pool->join();
+    LOGV2_DEBUG(
+        4910802, kDiagnosticLogLevel, "Stopped asynchronous request executor", "name"_attr = _name);
+}
+
+Future<void> AsyncRequestExecutor::schedule(std::shared_ptr<RequestExecutionContext> rec) {
+    auto opCtx = rec->getOpCtx();
+    auto [promise, future] = makePromiseFuture<void>();
+
+    // `this` remains valid as it owns the instance of thread pool.
+    _pool->schedule([this,
+                     strand = ClientStrand::get(opCtx->getClient()),
+                     promise = std::move(promise),
+                     rec = std::move(rec)](Status status) mutable {
+        hangBeforeRunningAsyncRequestExecutorTask.pauseWhileSet();
+        strand->run([&] {
+            promise.setWith([&] {
+                if (MONGO_unlikely(!status.isOK()))
+                    return status.withContext("Unable to schedule asynchronous request");
+
+                auto opCtx = rec->getOpCtx();
+                if (opCtx->isKillPending())
+                    return Status(opCtx->getKillStatus(), "Asynchronous operation was interrupted");
+
+                return handleRequest(std::move(rec));
+            });
+        });
+    });
+
+    return std::move(future);
+}
+
+}  // namespace mongo
diff --git a/src/mongo/executor/async_request_executor.h b/src/mongo/executor/async_request_executor.h
new file mode 100644
index 00000000000..a54e7848392
--- /dev/null
+++ b/src/mongo/executor/async_request_executor.h
@@ -0,0 +1,73 @@
+/**
+ *    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.
+ */
+
+#pragma once
+
+#include <memory>
+#include <string>
+
+#include "mongo/db/request_execution_context.h"
+#include "mongo/util/concurrency/thread_pool.h"
+#include "mongo/util/future.h"
+
+namespace mongo {
+
+/**
+ * The base class for constructing command-specific asynchronous executors.
+ * Requests (i.e., instances of `RequestExecutionContext`) are scheduled on a thread-pool, and
+ * passed to the command-specific implementation of `handleRequest`.
+ */
+class AsyncRequestExecutor {
+public:
+    AsyncRequestExecutor(AsyncRequestExecutor&&) = delete;
+    AsyncRequestExecutor(const AsyncRequestExecutor&) = delete;
+
+    explicit AsyncRequestExecutor(std::string name);
+    ~AsyncRequestExecutor();
+
+    /**
+     * Runs the command-specific code to handle the request.
+     * Must only access the request on the corresponding client thread.
+     */
+    virtual Status handleRequest(std::shared_ptr<RequestExecutionContext>) = 0;
+
+    /**
+     * Schedules the request on a thread pool (i.e., `_pool`) and calls into `handleRequest` to
+     * asynchronously execute the command.
+     */
+    Future<void> schedule(std::shared_ptr<RequestExecutionContext> rec);
+
+    static constexpr auto kDiagnosticLogLevel = 4;
+
+private:
+    const std::string _name;
+    std::unique_ptr<ThreadPool> _pool;
+};
+
+}  // namespace mongo