SERVER-15901: Periodically cleanup unused lock heads

(cherry-picked from 8e6e1d78c4c170384e024747737c94542f9f60d3)
(cherry-picked from dd6c44de50bea877ab865fdb95aa3eeffce649b9)
(cherry-picked from 328aa5b207117e6ef09605b732ff94f782af5c36)

Conflicts:
	src/mongo/db/concurrency/SConscript

3 files changed, 26 insertions, 0 deletions

diff --git a/src/mongo/db/concurrency/SConscript b/src/mongo/db/concurrency/SConscript
index 1687fa6ce04..de02e4d0671 100644
--- a/src/mongo/db/concurrency/SConscript
+++ b/src/mongo/db/concurrency/SConscript
@@ -21,9 +21,12 @@ env.Library(
         'lock_stats.cpp',
     ],
     LIBDEPS=[
+        '$BUILD_DIR/mongo/background_job',
         '$BUILD_DIR/mongo/base/base',
         '$BUILD_DIR/mongo/foundation',
         '$BUILD_DIR/mongo/global_environment_experiment',
+        # Temporary crutch since the ssl cleanup is hard coded in background.cpp
+        '$BUILD_DIR/mongo/network',
         "$BUILD_DIR/mongo/server_parameters",
         '$BUILD_DIR/mongo/spin_lock',
         '$BUILD_DIR/third_party/shim_boost',
diff --git a/src/mongo/db/concurrency/lock_manager.cpp b/src/mongo/db/concurrency/lock_manager.cpp
index f50a0e07531..0c66d73a053 100644
--- a/src/mongo/db/concurrency/lock_manager.cpp
+++ b/src/mongo/db/concurrency/lock_manager.cpp
@@ -677,6 +677,7 @@ namespace {
     }
 
     void LockManager::cleanupUnusedLocks() {
+        size_t deletedLockHeads = 0;
         for (unsigned i = 0; i < _numLockBuckets; i++) {
             LockBucket* bucket = &_lockBuckets[i];
             SimpleMutex::scoped_lock scopedLock(bucket->mutex);
@@ -698,6 +699,7 @@ namespace {
                     invariant(lock->compatibleFirstCount == 0);
 
                     bucket->data.erase(it++);
+                    deletedLockHeads++;
                     delete lock;
                 }
                 else {
diff --git a/src/mongo/db/concurrency/lock_state.cpp b/src/mongo/db/concurrency/lock_state.cpp
index fc1fec11980..15274a40877 100644
--- a/src/mongo/db/concurrency/lock_state.cpp
+++ b/src/mongo/db/concurrency/lock_state.cpp
@@ -37,6 +37,7 @@
 #include "mongo/db/global_environment_experiment.h"
 #include "mongo/db/namespace_string.h"
 #include "mongo/platform/compiler.h"
+#include "mongo/util/background.h"
 #include "mongo/util/concurrency/synchronization.h"
 #include "mongo/util/debug_util.h"
 #include "mongo/util/log.h"
@@ -869,6 +870,26 @@ namespace {
     }
 
 
+namespace {
+    /**
+     *  Periodically purges unused lock buckets. The first time the lock is used again after
+     *  cleanup it needs to be allocated, and similarly, every first use by a client for an intent
+     *  mode may need to create a partitioned lock head. Cleanup is done roughtly once a minute.
+     */
+    class UnusedLockCleaner : PeriodicTask {
+    public:
+        std::string taskName() const {
+            return "UnusedLockCleaner";
+        }
+
+        void taskDoWork() {
+            LOG(2) << "cleaning up unused lock buckets of the global lock manager";
+            getGlobalLockManager()->cleanupUnusedLocks();
+        }
+    } unusedLockCleaner;
+} // namespace
+
+
     //
     // Standalone functions
     //