SERVER-14668 Change read paths to acquire IS lock on the DB instead of S

Also change respective assertions, which are checking for S-lock on the
database.

8 files changed, 40 insertions, 27 deletions

diff --git a/src/mongo/db/concurrency/d_concurrency.cpp b/src/mongo/db/concurrency/d_concurrency.cpp
index bdd78c68f83..1e33f5246e7 100644
--- a/src/mongo/db/concurrency/d_concurrency.cpp
+++ b/src/mongo/db/concurrency/d_concurrency.cpp
@@ -259,11 +259,11 @@ namespace mongo {
 
         _lockState->lockGlobal(isRead ? newlm::MODE_IS : newlm::MODE_IX);
 
-        if (supportsDocLocking()) {
+        if (supportsDocLocking() || isRead) {
             _lockState->lock(_id, _mode);
         }
         else {
-            _lockState->lock(_id, isRead ? newlm::MODE_S : newlm::MODE_X);
+            _lockState->lock(_id, newlm::MODE_X);
         }
 
         resetTime();
diff --git a/src/mongo/db/concurrency/lock_state.cpp b/src/mongo/db/concurrency/lock_state.cpp
index 777e482991a..b9f6d037798 100644
--- a/src/mongo/db/concurrency/lock_state.cpp
+++ b/src/mongo/db/concurrency/lock_state.cpp
@@ -63,6 +63,10 @@ namespace newlm {
 
         const ResourceId resourceIdLocalDB =
                                 ResourceId(RESOURCE_DATABASE, string("local"));
+
+        bool isSharedMode(newlm::LockMode mode) {
+            return (mode == newlm::MODE_IS || mode == newlm::MODE_S);
+        }
     }
 
 
@@ -98,6 +102,19 @@ namespace newlm {
         return isLockHeldForMode(resIdNs, newlm::MODE_X);
     }
 
+    bool LockerImpl::isDbLockedForMode(const StringData& dbName, newlm::LockMode mode) const {
+        DEV {
+            const NamespaceString nss(dbName);
+            dassert(nss.coll().empty());
+        };
+
+        if (isW()) return true;
+        if (isR() && isSharedMode(mode)) return true;
+
+        const newlm::ResourceId resIdDb(newlm::RESOURCE_DATABASE, dbName);
+        return isLockHeldForMode(resIdDb, mode);
+    }
+
     bool LockerImpl::isAtLeastReadLocked(const StringData& ns) const {
         if (threadState() == 'R' || threadState() == 'W') {
             return true; // global
@@ -139,15 +156,6 @@ namespace newlm {
         }
     }
 
-    void LockerImpl::assertAtLeastReadLocked(const StringData& ns) const {
-        if (!isAtLeastReadLocked(ns)) {
-            log() << "error expected " << ns << " to be locked " << std::endl;
-            dump();
-            msgasserted(
-                16104, mongoutils::str::stream() << "expected to be read locked for " << ns);
-        }
-    }
-
     BSONObj LockerImpl::reportState() {
         BSONObjBuilder b;
         reportState(&b);
diff --git a/src/mongo/db/concurrency/lock_state.h b/src/mongo/db/concurrency/lock_state.h
index 3c710a03b1d..2201a4fc9e0 100644
--- a/src/mongo/db/concurrency/lock_state.h
+++ b/src/mongo/db/concurrency/lock_state.h
@@ -217,11 +217,11 @@ namespace newlm {
         virtual bool isLocked() const;
         virtual bool isWriteLocked() const;
         virtual bool isWriteLocked(const StringData& ns) const;
+        virtual bool isDbLockedForMode(const StringData& dbName, newlm::LockMode mode) const;
         virtual bool isAtLeastReadLocked(const StringData& ns) const;
         virtual bool isRecursive() const;
 
         virtual void assertWriteLocked(const StringData& ns) const;
-        virtual void assertAtLeastReadLocked(const StringData& ns) const;
 
         /** 
          * Pending means we are currently trying to get a lock.
diff --git a/src/mongo/db/concurrency/locker.h b/src/mongo/db/concurrency/locker.h
index e059a30d434..e8d68eafdd3 100644
--- a/src/mongo/db/concurrency/locker.h
+++ b/src/mongo/db/concurrency/locker.h
@@ -222,11 +222,11 @@ namespace mongo {
         virtual bool isLocked() const = 0;
         virtual bool isWriteLocked() const = 0;
         virtual bool isWriteLocked(const StringData& ns) const = 0;
+        virtual bool isDbLockedForMode(const StringData& dbName, newlm::LockMode mode) const = 0;
         virtual bool isAtLeastReadLocked(const StringData& ns) const = 0;
         virtual bool isRecursive() const = 0;
 
         virtual void assertWriteLocked(const StringData& ns) const = 0;
-        virtual void assertAtLeastReadLocked(const StringData& ns) const = 0;
 
         /** pending means we are currently trying to get a lock */
         virtual bool hasLockPending() const = 0;
diff --git a/src/mongo/db/dbhelpers.cpp b/src/mongo/db/dbhelpers.cpp
index a2f5e964a70..d8de49742fb 100644
--- a/src/mongo/db/dbhelpers.cpp
+++ b/src/mongo/db/dbhelpers.cpp
@@ -144,8 +144,8 @@ namespace mongo {
                            BSONObj& result,
                            bool* nsFound,
                            bool* indexFound) {
-        txn->lockState()->assertAtLeastReadLocked(ns);
-        invariant( database );
+
+        invariant(database);
 
         Collection* collection = database->getCollection( txn, ns );
         if ( !collection ) {
diff --git a/src/mongo/db/pipeline/pipeline_d.cpp b/src/mongo/db/pipeline/pipeline_d.cpp
index b9d4ca9795e..90706aed99b 100644
--- a/src/mongo/db/pipeline/pipeline_d.cpp
+++ b/src/mongo/db/pipeline/pipeline_d.cpp
@@ -81,7 +81,6 @@ namespace {
             const intrusive_ptr<ExpressionContext>& pExpCtx) {
         // get the full "namespace" name
         const string& fullName = pExpCtx->ns.ns();
-        pExpCtx->opCtx->lockState()->assertAtLeastReadLocked(fullName);
 
         // We will be modifying the source vector as we go
         Pipeline::SourceContainer& sources = pPipeline->sources;
diff --git a/src/mongo/db/prefetch.cpp b/src/mongo/db/prefetch.cpp
index 2bda9526e42..958f6039046 100644
--- a/src/mongo/db/prefetch.cpp
+++ b/src/mongo/db/prefetch.cpp
@@ -172,7 +172,10 @@ namespace {
         BSONObj obj = op.getObjectField(opField);
         const char *ns = op.getStringField("ns");
 
-        txn->lockState()->assertAtLeastReadLocked(ns);
+        // This will have to change for engines other than MMAP V1, because they might not have
+        // means for directly prefetching pages from the collection. For this purpose, acquire S
+        // lock on the database, instead of optimizing with IS.
+        Lock::CollectionLock collLock(txn->lockState(), ns, newlm::MODE_S);
 
         Collection* collection = db->getCollection( txn, ns );
         if (!collection) {
diff --git a/src/mongo/db/storage/mmap_v1/mmap_v1_extent_manager.cpp b/src/mongo/db/storage/mmap_v1/mmap_v1_extent_manager.cpp
index 07bd682d3dc..6e2696a7a2f 100644
--- a/src/mongo/db/storage/mmap_v1/mmap_v1_extent_manager.cpp
+++ b/src/mongo/db/storage/mmap_v1/mmap_v1_extent_manager.cpp
@@ -138,8 +138,13 @@ namespace mongo {
                                       int n,
                                       int sizeNeeded ,
                                       bool preallocateOnly) {
-        verify(this);
-        DEV txn->lockState()->assertAtLeastReadLocked( _dbname );
+
+        if (!txn->lockState()->isWriteLocked(_dbname)) {
+            log() << "error: getFile() called in a read lock, yet file to return is not yet open";
+            log() << "       getFile(" << n << ") _files.size:" 
+                  <<_files.size() << ' ' << fileName(n).string();
+            invariant(false);
+        }
 
         if ( n < 0 || n >= DiskLoc::MaxFiles ) {
             log() << "getFile(): n=" << n << endl;
@@ -151,22 +156,20 @@ namespace mongo {
                 log() << "getFile(): n=" << n << endl;
             }
         }
+
         DataFile* p = 0;
         if ( !preallocateOnly ) {
             while ( n >= (int) _files.size() ) {
-                verify(this);
-                if (!txn->lockState()->isWriteLocked(_dbname)) {
-                    log() << "error: getFile() called in a read lock, yet file to return is not yet open";
-                    log() << "       getFile(" << n << ") _files.size:" <<_files.size() << ' ' << fileName(n).string();
-                    invariant(false);
-                }
                 _files.push_back(0);
             }
             p = _files[n];
         }
+
         if ( p == 0 ) {
-            if ( n == 0 ) audit::logCreateDatabase( currentClient.get(), _dbname );
-            DEV txn->lockState()->assertWriteLocked( _dbname );
+            if (n == 0) {
+                audit::logCreateDatabase(currentClient.get(), _dbname);
+            }
+
             boost::filesystem::path fullName = fileName( n );
             string fullNameString = fullName.string();
             p = new DataFile(n);