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

1 files changed, 111 insertions, 0 deletions

diff --git a/src/mongo/db/client_out_of_line_executor.cpp b/src/mongo/db/client_out_of_line_executor.cpp
new file mode 100644
index 00000000000..2fd1787a7f1
--- /dev/null
+++ b/src/mongo/db/client_out_of_line_executor.cpp
@@ -0,0 +1,111 @@
+/**
+ *    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::kDefault
+
+#include "mongo/db/client_out_of_line_executor.h"
+
+#include "mongo/base/error_codes.h"
+#include "mongo/base/status.h"
+#include "mongo/logger/log_severity_limiter.h"
+#include "mongo/logv2/log.h"
+#include "mongo/util/scopeguard.h"
+
+namespace mongo {
+
+ClientOutOfLineExecutor::ClientOutOfLineExecutor() noexcept {
+    _taskQueue = std::make_shared<QueueType>();
+}
+
+ClientOutOfLineExecutor::~ClientOutOfLineExecutor() noexcept {
+    // Force producers to consume their tasks beyond this point.
+    _taskQueue->closeProducerEnd();
+
+    // Only call `tryPop()` when there's a task to pop to avoid lifetime issues with logging.
+    auto toCollect = _taskQueue->getStats().queueDepth;
+    while (toCollect) {
+        auto task = _taskQueue->tryPop();
+        invariant(task);
+        (*task)(Status(ErrorCodes::ClientDisconnect, "Client's executor has stopped"));
+        toCollect--;
+    }
+    invariant(toCollect == 0);
+}
+
+static const Client::Decoration<ClientOutOfLineExecutor> getClientExecutor =
+    Client::declareDecoration<ClientOutOfLineExecutor>();
+
+ClientOutOfLineExecutor* ClientOutOfLineExecutor::get(const Client* client) noexcept {
+    return const_cast<ClientOutOfLineExecutor*>(&getClientExecutor(client));
+}
+
+void ClientOutOfLineExecutor::schedule(Task task) {
+    _taskQueue->push(std::move(task));
+}
+
+void ClientOutOfLineExecutor::consumeAllTasks() noexcept {
+    // This limit allows logging incidents that the executor consumes too much of the client's
+    // time running scheduled tasks. The value is only used for debugging, and should be an
+    // approximation of the acceptable overhead in the context of normal client operations.
+    static constexpr auto kTimeLimit = Microseconds(30);
+
+    _stopWatch.restart();
+
+    while (auto maybeTask = _taskQueue->tryPop()) {
+        auto task = std::move(*maybeTask);
+        task(Status::OK());
+    }
+
+    auto elapsed = _stopWatch.elapsed();
+
+    auto severity = MONGO_GET_LIMITED_SEVERITY(this, Seconds{1}, 0, 2);
+    if (MONGO_unlikely(elapsed > kTimeLimit)) {
+        LOGV2_DEBUG(4651401,
+                    logSeverityV1toV2(severity).toInt(),
+                    "Client's executor exceeded time limit",
+                    "elapsed"_attr = elapsed,
+                    "limit"_attr = kTimeLimit);
+    }
+}
+
+void ClientOutOfLineExecutor::QueueHandle::schedule(Task&& task) {
+    auto guard = makeGuard(
+        [&task] { task(Status(ErrorCodes::CallbackCanceled, "Client no longer exists")); });
+
+    if (auto queue = _weakQueue.lock()) {
+        try {
+            queue->push(std::move(task));
+            guard.dismiss();
+        } catch (const ExceptionFor<ErrorCodes::ProducerConsumerQueueEndClosed>&) {
+            // The destructor for the out-of-line executor has already been called.
+        }
+    }
+}
+
+}  // namespace mongo