SERVER-21436 NetworkInterfaceThreadPool for sharding

Adding a new kind of thread pool that dispatches jobs onto a provided
NetworkInterface rather than using their own thread pool.

We're also switching the ThreadPoolTaskExecutor to use this instead of
the regular thread pool for sharding.  That, in turn, removes context
switches by allowing inline execution of scheduled tasks if they're
invoked from a nia io_worker.

In pursuit of this, factored the connection pool tests out into a common
set that the NetworkInterfaceThreadPool can use.

1 files changed, 79 insertions, 0 deletions

diff --git a/src/mongo/executor/network_interface_thread_pool.h b/src/mongo/executor/network_interface_thread_pool.h
new file mode 100644
index 00000000000..bf139cccf01
--- /dev/null
+++ b/src/mongo/executor/network_interface_thread_pool.h
@@ -0,0 +1,79 @@
+/**
+ *    Copyright (C) 2015 MongoDB Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    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
+ *    GNU Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    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 GNU Affero General 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 <cstdint>
+#include <vector>
+
+#include "mongo/stdx/condition_variable.h"
+#include "mongo/stdx/mutex.h"
+#include "mongo/util/concurrency/thread_pool_interface.h"
+
+namespace mongo {
+namespace executor {
+
+class NetworkInterface;
+
+/**
+ * A Thread Pool implementation based on running tasks on the background thread
+ * of some Network Interface.
+ *
+ * The basic idea is to triage tasks, running them immediately if we're invoked
+ * from on the network interface thread, and queueing them up to be drained by
+ * a setAlarm if not.
+ */
+class NetworkInterfaceThreadPool final : public ThreadPoolInterface {
+public:
+    NetworkInterfaceThreadPool(NetworkInterface* net);
+    ~NetworkInterfaceThreadPool() override;
+
+    void startup() override;
+    void shutdown() override;
+    void join() override;
+    Status schedule(Task task) override;
+
+private:
+    void consumeTasks(stdx::unique_lock<stdx::mutex> lk);
+    void dtorImpl();
+
+    NetworkInterface* const _net;
+
+    // Protects all of the pool state below
+    stdx::mutex _mutex;
+    stdx::condition_variable _joiningCondition;
+    std::vector<Task> _tasks;
+    bool _started = false;
+    bool _inShutdown = false;
+    bool _joining = false;
+    bool _registeredAlarm = false;
+    bool _consumingTasks = false;
+};
+
+}  // namespace executor
+}  // namespace mongo