SERVER-19001 Implementation of ThreadPoolTaskExecutor and basic tests.

In order to support deterministic unit testing, it was also necessary to
introduce a mock implementation of ThreadPool, executor::ThreadPoolMock,
that is tightly integrated with NetworkInterfaceMock to allow for
deterministic unit testing of things that use TaskExecutors.

To keep the ThreadPoolTaskExecutor from having to keep a dedicated
thread for handling scheduleAt(Date_t, ...) processing, a new method,
setAlarm, is introduced to NetworkInterface. setAlarm offers an
extremely relaxed contract, to maximize the number of legal implementations.

1 files changed, 134 insertions, 0 deletions

diff --git a/src/mongo/executor/thread_pool_mock.cpp b/src/mongo/executor/thread_pool_mock.cpp
new file mode 100644
index 00000000000..ab7c9ddfda4
--- /dev/null
+++ b/src/mongo/executor/thread_pool_mock.cpp
@@ -0,0 +1,134 @@
+/**
+ *    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.
+ */
+
+#define MONGO_LOG_DEFAULT_COMPONENT mongo::logger::LogComponent::kExecutor
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/executor/thread_pool_mock.h"
+
+#include "mongo/executor/network_interface_mock.h"
+#include "mongo/util/log.h"
+
+namespace mongo {
+namespace executor {
+
+ThreadPoolMock::ThreadPoolMock(NetworkInterfaceMock* net, int32_t prngSeed)
+    : _prng(prngSeed), _net(net) {}
+
+ThreadPoolMock::~ThreadPoolMock() {
+    stdx::unique_lock<stdx::mutex> lk(_mutex);
+    _inShutdown = true;
+    _net->signalWorkAvailable();
+    if (_started) {
+        if (_worker.joinable()) {
+            lk.unlock();
+            _worker.join();
+            lk.lock();
+        }
+    } else {
+        consumeTasks(&lk);
+    }
+    invariant(_tasks.empty());
+}
+
+void ThreadPoolMock::startup() {
+    log() << "Starting pool";
+    stdx::lock_guard<stdx::mutex> lk(_mutex);
+    invariant(!_started);
+    invariant(!_worker.joinable());
+    _started = true;
+    _worker = stdx::thread([this] {
+        stdx::unique_lock<stdx::mutex> lk(_mutex);
+        consumeTasks(&lk);
+    });
+}
+
+void ThreadPoolMock::shutdown() {
+    stdx::lock_guard<stdx::mutex> lk(_mutex);
+    _inShutdown = true;
+    _net->signalWorkAvailable();
+}
+
+void ThreadPoolMock::join() {
+    stdx::unique_lock<stdx::mutex> lk(_mutex);
+    _joining = true;
+    if (_started) {
+        stdx::thread toJoin = std::move(_worker);
+        _net->signalWorkAvailable();
+        lk.unlock();
+        toJoin.join();
+        lk.lock();
+        invariant(_tasks.empty());
+    } else {
+        consumeTasks(&lk);
+        invariant(_tasks.empty());
+    }
+}
+
+Status ThreadPoolMock::schedule(Task task) {
+    stdx::lock_guard<stdx::mutex> lk(_mutex);
+    if (_inShutdown) {
+        return {ErrorCodes::ShutdownInProgress, "Shutdown in progress"};
+    }
+    _tasks.emplace_back(std::move(task));
+    return Status::OK();
+}
+
+void ThreadPoolMock::consumeTasks(stdx::unique_lock<stdx::mutex>* lk) {
+    using std::swap;
+    log() << "Starting to consume tasks";
+    while (!(_inShutdown && _tasks.empty())) {
+        if (_tasks.empty()) {
+            lk->unlock();
+            _net->waitForWork();
+            lk->lock();
+            continue;
+        }
+        auto next = static_cast<size_t>(_prng.nextInt64(static_cast<int64_t>(_tasks.size())));
+        if (next + 1 != _tasks.size()) {
+            swap(_tasks[next], _tasks.back());
+        }
+        Task fn = std::move(_tasks.back());
+        _tasks.pop_back();
+        lk->unlock();
+        fn();
+        lk->lock();
+    }
+    log() << "Done consuming tasks";
+    invariant(_tasks.empty());
+    while (!_joining) {
+        lk->unlock();
+        _net->waitForWork();
+        lk->lock();
+    }
+    log() << "Ready to join";
+}
+
+}  // namespace executor
+}  // namespace mongo