SERVER-50678 Implement lock-free version of AutoGetCollection

2 files changed, 33 insertions, 11 deletions

diff --git a/src/mongo/db/concurrency/d_concurrency.cpp b/src/mongo/db/concurrency/d_concurrency.cpp
index a48d176689e..ea4738e55aa 100644
--- a/src/mongo/db/concurrency/d_concurrency.cpp
+++ b/src/mongo/db/concurrency/d_concurrency.cpp
@@ -139,11 +139,13 @@ bool Lock::ResourceMutex::isAtLeastReadLocked(Locker* locker) {
 Lock::GlobalLock::GlobalLock(OperationContext* opCtx,
                              LockMode lockMode,
                              Date_t deadline,
-                             InterruptBehavior behavior)
+                             InterruptBehavior behavior,
+                             bool skipRSTLLock)
     : _opCtx(opCtx),
       _result(LOCK_INVALID),
       _pbwm(opCtx->lockState(), resourceIdParallelBatchWriterMode),
       _interruptBehavior(behavior),
+      _skipRSTLLock(skipRSTLLock),
       _isOutermostLock(!opCtx->lockState()->isLocked()) {
     _opCtx->lockState()->getFlowControlTicket(_opCtx, lockMode);
 
@@ -157,17 +159,14 @@ Lock::GlobalLock::GlobalLock(OperationContext* opCtx,
             }
         });
 
-        _opCtx->lockState()->lock(
-            _opCtx, resourceIdReplicationStateTransitionLock, MODE_IX, deadline);
-
-        auto unlockRSTL = makeGuard(
-            [this] { _opCtx->lockState()->unlock(resourceIdReplicationStateTransitionLock); });
-
         _result = LOCK_INVALID;
-        _opCtx->lockState()->lockGlobal(_opCtx, lockMode, deadline);
+        if (skipRSTLLock) {
+            _takeGlobalLockOnly(lockMode, deadline);
+        } else {
+            _takeGlobalAndRSTLLocks(lockMode, deadline);
+        }
         _result = LOCK_OK;
 
-        unlockRSTL.dismiss();
         unlockPBWM.dismiss();
     } catch (const ExceptionForCat<ErrorCategory::Interruption>&) {
         // The kLeaveUnlocked behavior suppresses this exception.
@@ -178,11 +177,26 @@ Lock::GlobalLock::GlobalLock(OperationContext* opCtx,
     _opCtx->lockState()->setGlobalLockTakenInMode(acquiredLockMode);
 }
 
+void Lock::GlobalLock::_takeGlobalLockOnly(LockMode lockMode, Date_t deadline) {
+    _opCtx->lockState()->lockGlobal(_opCtx, lockMode, deadline);
+}
+
+void Lock::GlobalLock::_takeGlobalAndRSTLLocks(LockMode lockMode, Date_t deadline) {
+    _opCtx->lockState()->lock(_opCtx, resourceIdReplicationStateTransitionLock, MODE_IX, deadline);
+    auto unlockRSTL = makeGuard(
+        [this] { _opCtx->lockState()->unlock(resourceIdReplicationStateTransitionLock); });
+
+    _opCtx->lockState()->lockGlobal(_opCtx, lockMode, deadline);
+
+    unlockRSTL.dismiss();
+}
+
 Lock::GlobalLock::GlobalLock(GlobalLock&& otherLock)
     : _opCtx(otherLock._opCtx),
       _result(otherLock._result),
       _pbwm(std::move(otherLock._pbwm)),
       _interruptBehavior(otherLock._interruptBehavior),
+      _skipRSTLLock(otherLock._skipRSTLLock),
       _isOutermostLock(otherLock._isOutermostLock) {
     // Mark as moved so the destructor doesn't invalidate the newly-constructed lock.
     otherLock._result = LOCK_INVALID;
diff --git a/src/mongo/db/concurrency/d_concurrency.h b/src/mongo/db/concurrency/d_concurrency.h
index 187cb3d5a41..4ae7af8cdb9 100644
--- a/src/mongo/db/concurrency/d_concurrency.h
+++ b/src/mongo/db/concurrency/d_concurrency.h
@@ -221,7 +221,8 @@ public:
         GlobalLock(OperationContext* opCtx,
                    LockMode lockMode,
                    Date_t deadline,
-                   InterruptBehavior behavior);
+                   InterruptBehavior behavior,
+                   bool skipRSTLLock = false);
 
         GlobalLock(GlobalLock&&);
 
@@ -239,7 +240,7 @@ public:
                 }
                 _unlock();
             }
-            if (lockResult == LOCK_OK || lockResult == LOCK_WAITING) {
+            if (!_skipRSTLLock && (lockResult == LOCK_OK || lockResult == LOCK_WAITING)) {
                 _opCtx->lockState()->unlock(resourceIdReplicationStateTransitionLock);
             }
         }
@@ -249,12 +250,19 @@ public:
         }
 
     private:
+        /**
+         * Constructor helper functions, to handle skipping or taking the RSTL lock.
+         */
+        void _takeGlobalLockOnly(LockMode lockMode, Date_t deadline);
+        void _takeGlobalAndRSTLLocks(LockMode lockMode, Date_t deadline);
+
         void _unlock();
 
         OperationContext* const _opCtx;
         LockResult _result;
         ResourceLock _pbwm;
         InterruptBehavior _interruptBehavior;
+        bool _skipRSTLLock;
         const bool _isOutermostLock;
     };