Optimized the shared counter generator to avoid LM calls if there's no contention on the protecting lock.

src/jrd/Database.cpp

@@ -156,13 +156,18 @@ namespace Jrd
 			lock->lck_object = counter;
 			LCK_lock(tdbb, lock, LCK_PW, LCK_WAIT);
 
+			counter->isProtected = true;
 			counter->curVal = 1;
 			counter->maxVal = 0;
 		}
 
 		if (counter->curVal > counter->maxVal)
 		{
-			LCK_convert(tdbb, counter->lock, LCK_PW, LCK_WAIT);
+			if (!counter->isProtected)
+			{
+				LCK_convert(tdbb, counter->lock, LCK_PW, LCK_WAIT);
+				counter->isProtected = true;
+			}
 
 			counter->curVal = LCK_read_data(tdbb, counter->lock);
 
@@ -192,6 +197,7 @@ namespace Jrd
 			SyncLockGuard guard(&dbb->dbb_sh_counter_sync, SYNC_EXCLUSIVE, "Database::blockingAstSharedCounter");
 
 			LCK_downgrade(tdbb, counter->lock);
+			counter->isProtected = false;
 		}
 		catch (const Exception&)
 		{} // no-op

src/jrd/Database.h

@@ -236,9 +236,10 @@ public:
 
 		struct ValueCache
 		{
-			Lock* lock;		// lock which holds shared counter value
-			SLONG curVal;	// current value of shared counter lock
-			SLONG maxVal;	// maximum cached value of shared counter lock
+			Lock* lock;			// lock which holds shared counter value
+			bool isProtected;	// flag indicating that we own the lock in the PW mode
+			SLONG curVal;		// current value of shared counter lock
+			SLONG maxVal;		// maximum cached value of shared counter lock
 		};
 
 	public: