SERVER-33233 Don't stall ftdc due to running out of tickets

4 files changed, 38 insertions, 4 deletions

diff --git a/src/mongo/db/concurrency/d_concurrency_test.cpp b/src/mongo/db/concurrency/d_concurrency_test.cpp
index e2e881ef866..67b903c51af 100644
--- a/src/mongo/db/concurrency/d_concurrency_test.cpp
+++ b/src/mongo/db/concurrency/d_concurrency_test.cpp
@@ -62,12 +62,13 @@ const int kMinPerfMillis = 30;     // min duration for reliable timing
 class UseGlobalThrottling {
 public:
     explicit UseGlobalThrottling(OperationContext* opCtx, int numTickets)
-        : _opCtx(opCtx), _holder(1) {
+        : _opCtx(opCtx), _holder(numTickets) {
         _opCtx->lockState()->setGlobalThrottling(&_holder, &_holder);
     }
-    ~UseGlobalThrottling() {
+    ~UseGlobalThrottling() noexcept(false) {
         // Reset the global setting as we're about to destroy the ticket holder.
         _opCtx->lockState()->setGlobalThrottling(nullptr, nullptr);
+        ASSERT_EQ(_holder.used(), 0);
     }
 
 private:
@@ -1008,6 +1009,24 @@ TEST_F(DConcurrencyTestFixture, Throttling) {
     ASSERT(!overlongWait);
 }
 
+TEST_F(DConcurrencyTestFixture, NoThrottlingWhenNotAcquiringTickets) {
+    auto clientOpctxPairs = makeKClientsWithLockers<DefaultLockerImpl>(2);
+    auto opctx1 = clientOpctxPairs[0].second.get();
+    auto opctx2 = clientOpctxPairs[1].second.get();
+    // Limit the locker to 1 ticket at a time.
+    UseGlobalThrottling throttle(opctx1, 1);
+
+    // Prevent the enforcement of ticket throttling.
+    opctx1->lockState()->setShouldAcquireTicket(false);
+
+    // Both locks should be acquired immediately because there is no throttling.
+    Lock::GlobalRead R1(opctx1, Date_t::now());
+    ASSERT(R1.isLocked());
+
+    Lock::GlobalRead R2(opctx2, Date_t::now());
+    ASSERT(R2.isLocked());
+}
+
 TEST_F(DConcurrencyTestFixture, DBLockTimeout) {
     auto clientOpctxPairs = makeKClientsWithLockers<DefaultLockerImpl>(2);
     auto opctx1 = clientOpctxPairs[0].second.get();
diff --git a/src/mongo/db/concurrency/lock_state.cpp b/src/mongo/db/concurrency/lock_state.cpp
index 34645189977..4efdb1c49b6 100644
--- a/src/mongo/db/concurrency/lock_state.cpp
+++ b/src/mongo/db/concurrency/lock_state.cpp
@@ -301,7 +301,7 @@ LockResult LockerImpl<IsForMMAPV1>::_lockGlobalBegin(LockMode mode, Date_t deadl
     dassert(isLocked() == (_modeForTicket != MODE_NONE));
     if (_modeForTicket == MODE_NONE) {
         const bool reader = isSharedLockMode(mode);
-        auto holder = ticketHolders[mode];
+        auto holder = shouldAcquireTicket() ? ticketHolders[mode] : nullptr;
         if (holder) {
             _clientState.store(reader ? kQueuedReader : kQueuedWriter);
             if (deadline == Date_t::max()) {
@@ -810,7 +810,7 @@ bool LockerImpl<IsForMMAPV1>::_unlockImpl(LockRequestsMap::Iterator* it) {
     if (globalLockManager.unlock(it->objAddr())) {
         if (it->key() == resourceIdGlobal) {
             invariant(_modeForTicket != MODE_NONE);
-            auto holder = ticketHolders[_modeForTicket];
+            auto holder = shouldAcquireTicket() ? ticketHolders[_modeForTicket] : nullptr;
             _modeForTicket = MODE_NONE;
             if (holder) {
                 holder->release();
diff --git a/src/mongo/db/concurrency/locker.h b/src/mongo/db/concurrency/locker.h
index 3e70d000fe8..ff133800115 100644
--- a/src/mongo/db/concurrency/locker.h
+++ b/src/mongo/db/concurrency/locker.h
@@ -334,11 +334,25 @@ public:
         return _shouldConflictWithSecondaryBatchApplication;
     }
 
+    /**
+     * If set to false, this opts out of the ticket mechanism. This should be used sparingly
+     * for special purpose threads, such as FTDC.
+     */
+    void setShouldAcquireTicket(bool newValue) {
+        invariant(!isLocked());
+        _shouldAcquireTicket = newValue;
+    }
+    bool shouldAcquireTicket() const {
+        return _shouldAcquireTicket;
+    }
+
+
 protected:
     Locker() {}
 
 private:
     bool _shouldConflictWithSecondaryBatchApplication = true;
+    bool _shouldAcquireTicket = true;
 };
 
 }  // namespace mongo
diff --git a/src/mongo/db/ftdc/collector.cpp b/src/mongo/db/ftdc/collector.cpp
index 78e4f0de60a..c1e0c47158d 100644
--- a/src/mongo/db/ftdc/collector.cpp
+++ b/src/mongo/db/ftdc/collector.cpp
@@ -67,6 +67,7 @@ std::tuple<BSONObj, Date_t> FTDCCollectorCollection::collect(Client* client) {
     // batches that are taking a long time.
     auto opCtx = client->makeOperationContext();
     opCtx->lockState()->setShouldConflictWithSecondaryBatchApplication(false);
+    opCtx->lockState()->setShouldAcquireTicket(false);
 
     for (auto& collector : _collectors) {
         BSONObjBuilder subObjBuilder(builder.subobjStart(collector->name()));