SERVER-23243 Extract time-keeping from Listener

BackgroundThreadClockSource & FastClockSourceFactory

9 files changed, 377 insertions, 1 deletions

diff --git a/src/mongo/SConscript b/src/mongo/SConscript
index 0b65fb199a5..4dfa9e23441 100644
--- a/src/mongo/SConscript
+++ b/src/mongo/SConscript
@@ -250,6 +250,7 @@ mongodLibDeps = [
     "db/repl/storage_interface_impl",
     "executor/network_interface_factory",
     's/commands/shared_cluster_commands',
+    "util/clock_sources",
     "util/ntservice",
 ]
 
diff --git a/src/mongo/db/service_context.cpp b/src/mongo/db/service_context.cpp
index 075fafd7360..5bcf655cb93 100644
--- a/src/mongo/db/service_context.cpp
+++ b/src/mongo/db/service_context.cpp
@@ -147,6 +147,10 @@ TickSource* ServiceContext::getTickSource() const {
     return _tickSource.get();
 }
 
+ClockSource* ServiceContext::getFastClockSource() const {
+    return _fastClockSource.get();
+}
+
 ClockSource* ServiceContext::getPreciseClockSource() const {
     return _preciseClockSource.get();
 }
@@ -155,6 +159,10 @@ void ServiceContext::setTickSource(std::unique_ptr<TickSource> newSource) {
     _tickSource = std::move(newSource);
 }
 
+void ServiceContext::setFastClockSource(std::unique_ptr<ClockSource> newSource) {
+    _fastClockSource = std::move(newSource);
+}
+
 void ServiceContext::setPreciseClockSource(std::unique_ptr<ClockSource> newSource) {
     _preciseClockSource = std::move(newSource);
 }
diff --git a/src/mongo/db/service_context.h b/src/mongo/db/service_context.h
index 4a5b54bb6c7..6bf652eec43 100644
--- a/src/mongo/db/service_context.h
+++ b/src/mongo/db/service_context.h
@@ -35,8 +35,8 @@
 #include "mongo/db/storage/storage_engine.h"
 #include "mongo/platform/unordered_set.h"
 #include "mongo/stdx/functional.h"
-#include "mongo/util/decorable.h"
 #include "mongo/util/clock_source.h"
+#include "mongo/util/decorable.h"
 #include "mongo/util/tick_source.h"
 
 namespace mongo {
@@ -312,6 +312,16 @@ public:
      * Returns the tick/clock source set in this context.
      */
     TickSource* getTickSource() const;
+
+    /**
+     * Get a ClockSource implementation that may be less precise than the _preciseClockSource but
+     * may be cheaper to call.
+     */
+    ClockSource* getFastClockSource() const;
+
+    /**
+     * Get a ClockSource implementation that is very precise but may be expensive to call.
+     */
     ClockSource* getPreciseClockSource() const;
 
     /**
@@ -321,6 +331,12 @@ public:
     void setTickSource(std::unique_ptr<TickSource> newSource);
 
     /**
+     * Call this method with a ClockSource implementation that may be less precise than
+     * the _preciseClockSource but may be cheaper to call.
+     */
+    void setFastClockSource(std::unique_ptr<ClockSource> newSource);
+
+    /**
      * Call this method with a ClockSource implementation that is very precise but
      * may be expensive to call.
      */
@@ -348,6 +364,16 @@ private:
     ClientSet _clients;
 
     std::unique_ptr<TickSource> _tickSource;
+
+    /**
+     * A ClockSource implementation that may be less precise than the _preciseClockSource but
+     * may be cheaper to call.
+     */
+    std::unique_ptr<ClockSource> _fastClockSource;
+
+    /**
+     * A ClockSource implementation that is very precise but may be expensive to call.
+     */
     std::unique_ptr<ClockSource> _preciseClockSource;
 };
 
diff --git a/src/mongo/util/SConscript b/src/mongo/util/SConscript
index 60cf152be60..e03426cfdb3 100644
--- a/src/mongo/util/SConscript
+++ b/src/mongo/util/SConscript
@@ -293,6 +293,28 @@ env.Library(
     ],
 )
 
+env.Library(
+    target='clock_sources',
+    source=[
+        'background_thread_clock_source.cpp',
+        'fast_clock_source_factory.cpp',
+    ],
+    LIBDEPS=[
+        '$BUILD_DIR/mongo/base',
+    ],
+)
+
+env.CppUnitTest(
+    target='background_thread_clock_source_test',
+    source=[
+        'background_thread_clock_source_test.cpp',
+    ],
+    LIBDEPS=[
+        'clock_source_mock',
+        'clock_sources',
+    ],
+)
+
 if env.TargetOSIs('windows'):
     env.CppUnitTest(
         target='ntservice_test',
diff --git a/src/mongo/util/background_thread_clock_source.cpp b/src/mongo/util/background_thread_clock_source.cpp
new file mode 100644
index 00000000000..96dececff9c
--- /dev/null
+++ b/src/mongo/util/background_thread_clock_source.cpp
@@ -0,0 +1,80 @@
+/**
+ *    Copyright (C) 2016 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.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/util/background_thread_clock_source.h"
+
+#include <chrono>
+#include <thread>
+
+#include "mongo/stdx/memory.h"
+#include "mongo/stdx/thread.h"
+#include "mongo/util/time_support.h"
+
+namespace mongo {
+
+BackgroundThreadClockSource::BackgroundThreadClockSource(std::unique_ptr<ClockSource> clockSource,
+                                                         Milliseconds granularity)
+    : _clockSource(std::move(clockSource)), _granularity(granularity), _shutdownTimer(false) {
+    _updateCurrent();
+    _startTimerThread();
+}
+
+BackgroundThreadClockSource::~BackgroundThreadClockSource() {
+    {
+        stdx::unique_lock<stdx::mutex> lock(_mutex);
+        _shutdownTimer = true;
+        _condition.notify_one();
+    }
+
+    _timer.join();
+}
+
+Date_t BackgroundThreadClockSource::now() {
+    return Date_t::fromMillisSinceEpoch(_current.load());
+}
+
+void BackgroundThreadClockSource::_startTimerThread() {
+    // Start the background thread that repeatedly sleeps for the specified duration of milliseconds
+    // and wakes up to store the current time.
+    _timer = stdx::thread([&]() {
+        stdx::unique_lock<stdx::mutex> lock(_mutex);
+        while (!_shutdownTimer) {
+            if (_condition.wait_for(lock, _granularity) == stdx::cv_status::timeout) {
+                _updateCurrent();
+            }
+        }
+    });
+}
+
+void BackgroundThreadClockSource::_updateCurrent() {
+    _current.store(_clockSource->now().toMillisSinceEpoch());
+}
+
+}  // namespace mongo
diff --git a/src/mongo/util/background_thread_clock_source.h b/src/mongo/util/background_thread_clock_source.h
new file mode 100644
index 00000000000..eecd75c0f4c
--- /dev/null
+++ b/src/mongo/util/background_thread_clock_source.h
@@ -0,0 +1,73 @@
+/**
+ *    Copyright (C) 2016 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 <chrono>
+#include <thread>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/platform/atomic_word.h"
+#include "mongo/util/clock_source.h"
+#include "mongo/util/time_support.h"
+#include "mongo/stdx/condition_variable.h"
+#include "mongo/stdx/memory.h"
+#include "mongo/stdx/mutex.h"
+#include "mongo/stdx/thread.h"
+
+namespace mongo {
+
+/**
+ * A clock source that uses a periodic timer to build a low-resolution, fast-to-read clock.
+ * Essentially uses a background thread that repeatedly sleeps for X amount of milliseconds
+ * and wakes up to store the current time.
+ */
+class BackgroundThreadClockSource final : public ClockSource {
+    MONGO_DISALLOW_COPYING(BackgroundThreadClockSource);
+
+public:
+    BackgroundThreadClockSource(std::unique_ptr<ClockSource> clockSource, Milliseconds granularity);
+    ~BackgroundThreadClockSource() override;
+    Date_t now() override;
+
+private:
+    void _startTimerThread();
+    void _updateCurrent();
+
+    const std::unique_ptr<ClockSource> _clockSource;
+    AtomicInt64 _current;
+
+    const Milliseconds _granularity;
+
+    stdx::mutex _mutex;
+    stdx::condition_variable _condition;
+    bool _shutdownTimer;
+    stdx::thread _timer;
+};
+
+}  // namespace mongo
diff --git a/src/mongo/util/background_thread_clock_source_test.cpp b/src/mongo/util/background_thread_clock_source_test.cpp
new file mode 100644
index 00000000000..5bd82e4186e
--- /dev/null
+++ b/src/mongo/util/background_thread_clock_source_test.cpp
@@ -0,0 +1,67 @@
+/**
+ *    Copyright (C) 2016 10gen 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.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/stdx/memory.h"
+#include "mongo/unittest/unittest.h"
+#include "mongo/util/background_thread_clock_source.h"
+#include "mongo/util/clock_source.h"
+#include "mongo/util/clock_source_mock.h"
+#include "mongo/util/time_support.h"
+
+namespace {
+
+using namespace mongo;
+
+TEST(BackgroundThreadClockSource, CreateAndTerminate) {
+    auto clockSource = stdx::make_unique<ClockSourceMock>();
+    auto btClockSource =
+        stdx::make_unique<BackgroundThreadClockSource>(std::move(clockSource), Milliseconds(1));
+    btClockSource.reset();  // destroys the clock source
+
+    clockSource = stdx::make_unique<ClockSourceMock>();
+    btClockSource =
+        stdx::make_unique<BackgroundThreadClockSource>(std::move(clockSource), Hours(48));
+    btClockSource.reset();  // destroys the clock source
+}
+
+TEST(BackgroundThreadClockSource, TimeKeeping) {
+    auto clockSource = stdx::make_unique<ClockSourceMock>();
+    ClockSourceMock* clockSourceMock = clockSource.get();
+
+    auto btClockSource =
+        stdx::make_unique<BackgroundThreadClockSource>(std::move(clockSource), Milliseconds(1));
+    ASSERT_EQUALS(btClockSource->now(), clockSourceMock->now());
+
+    clockSourceMock->advance(Milliseconds(100));
+    sleepFor(Milliseconds(10));  // give the btClockSource opportunity to read the new time
+    ASSERT_EQUALS(btClockSource->now(), clockSourceMock->now());
+}
+
+}  // namespace
diff --git a/src/mongo/util/fast_clock_source_factory.cpp b/src/mongo/util/fast_clock_source_factory.cpp
new file mode 100644
index 00000000000..f0b7da62c09
--- /dev/null
+++ b/src/mongo/util/fast_clock_source_factory.cpp
@@ -0,0 +1,49 @@
+/**
+ *    Copyright (C) 2016 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.
+ */
+
+#include "mongo/platform/basic.h"
+
+#include "mongo/util/fast_clock_source_factory.h"
+
+#include <memory>
+
+#include "mongo/stdx/memory.h"
+#include "mongo/util/background_thread_clock_source.h"
+#include "mongo/util/system_clock_source.h"
+
+namespace mongo {
+
+std::unique_ptr<ClockSource> FastClockSourceFactory::create(Milliseconds granularity) {
+    // TODO: Create the fastest to read wall clock available on the system.
+    // For now, assume there is no built-in fast wall clock so instead
+    // create a background-thread-based timer.
+    return stdx::make_unique<BackgroundThreadClockSource>(
+        std::move(stdx::make_unique<SystemClockSource>()), granularity);
+}
+
+}  // namespace mongo
diff --git a/src/mongo/util/fast_clock_source_factory.h b/src/mongo/util/fast_clock_source_factory.h
new file mode 100644
index 00000000000..6d6de15d47f
--- /dev/null
+++ b/src/mongo/util/fast_clock_source_factory.h
@@ -0,0 +1,50 @@
+/**
+ *    Copyright (C) 2016 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 <memory>
+
+#include "mongo/util/time_support.h"
+
+namespace mongo {
+
+class ClockSource;
+
+// Factory that creates the fastest to read wall clock available on the system.
+class FastClockSourceFactory {
+public:
+    /**
+     * Creates the fastest to read wall clock available on the system.
+     * However, on systems with no built-in fast wall clock,
+     * creates a background-thread-based clock implementation.
+     */
+    static std::unique_ptr<ClockSource> create(Milliseconds granularity);
+};
+
+}  // namespace mongo