diff --git a/src/jrd/GlobalRWLock.cpp b/src/jrd/GlobalRWLock.cpp
new file mode 100644
index 0000000000..bed56fc266
--- /dev/null
+++ b/src/jrd/GlobalRWLock.cpp
@@ -0,0 +1,373 @@
+/*
+ *	PROGRAM:	JRD Access Method
+ *	MODULE:		GlobalRWLock.cpp
+ *	DESCRIPTION:	GlobalRWLock
+ *
+ *  The contents of this file are subject to the Initial
+ *  Developer's Public License Version 1.0 (the "License");
+ *  you may not use this file except in compliance with the
+ *  License. You may obtain a copy of the License at
+ *  http://www.ibphoenix.com/main.nfs?a=ibphoenix&page=ibp_idpl.
+ *
+ *  Software distributed under the License is distributed AS IS,
+ *  WITHOUT WARRANTY OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing rights
+ *  and limitations under the License.
+ *
+ *  The Original Code was created by Nickolay Samofatov
+ *  for the Firebird Open Source RDBMS project.
+ *
+ *  Copyright (c) 2006 Nickolay Samofatov
+ *  and all contributors signed below.
+ *
+ *  All Rights Reserved.
+ *  Contributor(s): ______________________________________.
+ *
+ *
+ */
+
+#include "firebird.h"
+#include "GlobalRWLock.h"
+#include "../lock/lock.h"
+#include "../lock/lock_proto.h"
+#include "iberr_proto.h"
+#include "isc_proto.h"
+#include "jrd.h"
+#include "lck_proto.h"
+#include "err_proto.h"
+
+#ifdef COS_DEBUG
+IMPLEMENT_TRACE_ROUTINE(cos_trace, "COS")
+#endif
+
+namespace Jrd {
+
+int GlobalRWLock::blocking_ast_cached_lock(void* ast_object)
+{
+	Jrd::GlobalRWLock *GlobalRWLock = 
+		static_cast<Jrd::GlobalRWLock*>(ast_object);
+
+	ISC_ast_enter();
+
+	/* Since this routine will be called asynchronously, we must establish
+		a thread context. */
+	Jrd::thread_db thd_context, *tdbb;
+	JRD_set_thread_data(tdbb, thd_context);
+
+	ISC_STATUS_ARRAY ast_status;
+	Jrd::Database* dbb = GlobalRWLock->cached_lock->lck_dbb;
+
+	tdbb->tdbb_database = dbb;
+	tdbb->tdbb_attachment = NULL;
+	tdbb->tdbb_quantum = QUANTUM;
+	tdbb->tdbb_request = NULL;
+	tdbb->tdbb_transaction = NULL;
+	tdbb->tdbb_status_vector = ast_status;
+
+	GlobalRWLock->blockingAstHandler(tdbb);
+
+	/* Restore the prior thread context */
+
+	JRD_restore_thread_data();
+
+	ISC_ast_exit();
+
+	return 0;	
+}
+
+GlobalRWLock::GlobalRWLock(thread_db* tdbb, MemoryPool& p, locktype_t lckType, 
+						   size_t lockLen, const UCHAR* lockStr, lck_owner_t physical_lock_owner,
+						   lck_owner_t default_logical_lock_owner, bool lock_caching)
+	: PermanentStorage(p), internal_blocking(0), external_blocking(false), 
+	  physicalLockOwner(physical_lock_owner), defaultLogicalLockOwner(default_logical_lock_owner), 
+	  lockCaching(lock_caching), readers(p)
+{
+	SET_TDBB(tdbb);
+
+	Database* dbb = tdbb->tdbb_database;
+
+	cached_lock = FB_NEW_RPT(getPool(), lockLen) Lock();
+	cached_lock->lck_type = static_cast<Jrd::lck_t>(lckType);
+	cached_lock->lck_owner_handle = 0;
+	cached_lock->lck_length = lockLen;
+
+	cached_lock->lck_dbb = dbb;
+	cached_lock->lck_parent = dbb->dbb_lock;
+	cached_lock->lck_object = reinterpret_cast<blk*>(this);
+	cached_lock->lck_ast = lockCaching ? blocking_ast_cached_lock : NULL;
+	memcpy(&cached_lock->lck_key, lockStr, lockLen);
+	
+	writer.owner_handle = 0;
+	writer.entry_count = 0;
+}
+
+GlobalRWLock::~GlobalRWLock()
+{
+	thread_db* tdbb = JRD_get_thread_data();
+	LCK_release(tdbb, cached_lock);
+	delete cached_lock;
+}
+
+bool GlobalRWLock::lock(thread_db* tdbb, locklevel_t level, SSHORT wait, SLONG owner_handle)
+{
+	SET_TDBB(tdbb);
+	fb_assert(owner_handle);
+
+	{ // this is a first scope for a code where counters are locked
+		CountersLockHolder lockHolder(lockMutex);
+
+	COS_TRACE(("lock type=%i, level=%i, readerscount=%i, owner=%i", cached_lock->lck_type, level, readers.getCount(), owner_handle));
+	// Check if this is a recursion case
+		size_t n;
+		if (level == LCK_read) {
+		if (readers.find(owner_handle, n)) {
+			readers[n].entry_count++;
+			return true;
+		}
+		} 
+		else {
+		if (writer.owner_handle == owner_handle) {
+			writer.entry_count++;
+			return true;
+		}
+	}
+
+	bool all_compatible = !writer.entry_count && (level == LCK_read || readers.getCount() == 0);
+
+	// We own the lock and all present requests are compatible with us
+	// In case of any congestion we force all requests through the lock
+	// manager to ensure lock ordering.
+	if (cached_lock->lck_physical >= level && all_compatible && 
+		!internal_blocking && !external_blocking) 
+	{
+		if (level == LCK_read) {
+			ObjectOwnerData ownerData;
+			ownerData.owner_handle = owner_handle;
+			ownerData.entry_count++;
+				readers.insert(n, ownerData);
+		}
+		else
+		{
+			writer.owner_handle = owner_handle;
+            writer.entry_count++;
+		}
+
+		return true;
+	}
+
+	// We need to release lock to get new level lock
+	if ( (cached_lock->lck_physical > 0) && (writer.entry_count == 0) && (readers.getCount() == 0) )
+	{
+		LCK_release(tdbb, cached_lock);
+		invalidate(tdbb, false);
+		external_blocking = false;
+		COS_TRACE(("release our lock to get new level lock, type=%i, level=%i", cached_lock->lck_type, cached_lock->lck_physical));
+	}
+
+	internal_blocking++;
+	}
+
+	// There is some congestion. Need to use the lock manager.
+	// Request new lock at the new level. Several concurrent lock requests may 
+	// wait here in the same process in parallel.
+	Lock* newLock = FB_NEW_RPT(getPool(), cached_lock->lck_length) Lock;
+	newLock->lck_type = cached_lock->lck_type;
+	newLock->lck_owner_handle = owner_handle;
+	newLock->lck_length = cached_lock->lck_length;
+
+	newLock->lck_dbb = cached_lock->lck_dbb;
+	newLock->lck_parent = cached_lock->lck_parent;
+	newLock->lck_object = cached_lock->lck_object;
+	newLock->lck_ast = cached_lock->lck_ast;
+	memcpy(&newLock->lck_key, &cached_lock->lck_key, cached_lock->lck_length);
+
+	COS_TRACE(("request new lock, type=%i, level=%i", cached_lock->lck_type, level));
+	if (!LCK_lock(tdbb, newLock, level, wait)) {
+		COS_TRACE(("Can't get a lock"));
+		delete newLock;
+		return false;
+	}
+	COS_TRACE(("Lock is got, type=%i", cached_lock->lck_type));
+
+	{ // this is a second scope for a code where counters are locked
+		CountersLockHolder lockHolder(lockMutex);
+
+	fb_assert(internal_blocking > 0);
+	internal_blocking--;
+
+	// Here old lock is not protecting shared object. We must refresh state by fetch.
+	if (newLock->lck_physical >= LCK_read) {
+		try {
+			fetch(tdbb);
+		} 
+		catch(const std::exception&) {
+			LCK_release(tdbb, newLock);
+			delete newLock;
+			return false;
+		}
+	}
+
+	if (level == LCK_read) {
+		ObjectOwnerData ownerData;
+		ownerData.entry_count++;
+		ownerData.owner_handle = owner_handle;
+		readers.add(ownerData);
+	}
+	else
+	{
+		writer.owner_handle = owner_handle;
+        writer.entry_count++;
+	}
+
+	// Replace cached lock with the new lock if needed
+	COS_TRACE(("Replace lock, type=%i", cached_lock->lck_type));
+	if (newLock->lck_physical > cached_lock->lck_physical) {
+		LCK_release(tdbb, cached_lock);
+		delete cached_lock;
+		cached_lock = newLock;
+		if (!LCK_set_owner_handle(tdbb, cached_lock, LCK_get_owner_handle_by_type(tdbb, physicalLockOwner))) {
+			COS_TRACE(("Error: set owner handle for captured lock, type=%i", cached_lock->lck_type));
+			LCK_release(tdbb, cached_lock);
+			return false;
+		}
+	}
+	else {
+		LCK_release(tdbb, newLock);
+		delete newLock;
+	}
+	}
+
+	return true;
+}
+
+// NOTE: unlock method must be signal safe
+// This function may be called in AST. The function doesn't wait.
+void GlobalRWLock::unlock(thread_db* tdbb, locklevel_t level, SLONG owner_handle)
+{
+	SET_TDBB(tdbb);
+
+	CountersLockHolder lockHolder(lockMutex);
+
+	COS_TRACE(("unlock level=%i", level));
+
+	// Check if this is a recursion case
+	if (level == LCK_read) {
+		size_t n;
+		if (!readers.find(owner_handle, n)) {
+			ERR_bugcheck_msg("Attempt to call GlobalRWLock::unlock() while not holding a valid lock for logical owner");
+		}
+		fb_assert(readers[n].entry_count > 0);
+		readers[n].entry_count--;
+		if (readers[n].entry_count == 0)
+			readers.remove(n);
+	}
+	else {
+		fb_assert(writer.owner_handle == owner_handle);
+		fb_assert(writer.entry_count == 1);
+		fb_assert(cached_lock->lck_physical == LCK_write);
+		
+		writer.entry_count = 0;
+		writer.owner_handle = 0;
+
+		// Optimize non-contention case - downgrade to PR and re-use the lock
+		if (!internal_blocking && !external_blocking && lockCaching)
+		{
+			if (!LCK_convert(tdbb, cached_lock, LCK_read, 0))
+				ERR_bugcheck_msg("LCK_convert call failed in GlobalRWLock::unlock()");
+			return;
+		}
+	}
+
+	if ( (readers.getCount() == 0) && (writer.entry_count == 0) ) {
+		COS_TRACE(("check for release a lock, type=%i", cached_lock->lck_type));
+		if (internal_blocking || !lockCaching) {
+			LCK_release(tdbb, cached_lock);
+			invalidate(tdbb, false);
+			external_blocking = false;
+		} 
+		else if (external_blocking) {
+			LCK_downgrade(tdbb, cached_lock);
+			if (cached_lock->lck_physical < LCK_read)
+				invalidate(tdbb, false);
+			external_blocking = false;
+		}
+	}
+
+	COS_TRACE(("unlock type=%i, level=%i, readerscount=%i, owner=%i", cached_lock->lck_type, level, readers.getCount(), owner_handle));
+}
+
+void GlobalRWLock::blockingAstHandler(thread_db* tdbb)
+{
+	SET_TDBB(tdbb);
+
+	CountersLockHolder lockHolder(lockMutex);
+
+	COS_TRACE_AST("bloackingAstHandler");
+	// When we request a new lock counters are not updated until we get it.
+	// As such, we need to check internal_blocking flag that is set during such situation.
+	if ( !internal_blocking && (readers.getCount() == 0) && (writer.entry_count == 0) ) {
+		COS_TRACE_AST("downgrade");
+		LCK_downgrade(tdbb, cached_lock);
+		if (cached_lock->lck_physical < LCK_read) {
+			invalidate(tdbb, true);
+			external_blocking = false;
+		}
+	}
+	else
+		external_blocking = true;
+}
+
+void GlobalRWLock::setLockData(SLONG lck_data)
+{
+	LCK_write_data(cached_lock, lck_data);
+} 
+
+void GlobalRWLock::changeLockOwner(thread_db* tdbb, locklevel_t level, SLONG old_owner_handle, SLONG new_owner_handle)
+{
+	SET_TDBB(tdbb);
+
+	if (old_owner_handle == new_owner_handle)
+		return;
+
+	CountersLockHolder lockHolder(lockMutex);
+
+	if (level == LCK_read) {
+		size_t n;
+		if (readers.find(old_owner_handle, n)) {
+			fb_assert(readers[n].entry_count > 0);
+			readers[n].entry_count--;
+			if (readers[n].entry_count == 0)
+				readers.remove(n);
+
+			if (readers.find(new_owner_handle, n))
+				readers[n].entry_count++;
+			else {
+				ObjectOwnerData ownerData;
+				ownerData.entry_count++;
+				ownerData.owner_handle = new_owner_handle;
+				readers.insert(n, ownerData);
+			}
+		}
+		else {
+			ERR_bugcheck_msg("Attempt to perform GlobalRWLock::change_lock_owner() while not holding a valid lock for logical owner");
+		}
+	}
+	else {
+		fb_assert(writer.entry_count == 1);
+		writer.owner_handle = new_owner_handle;
+	}
+}
+
+bool GlobalRWLock::tryReleaseLock(thread_db* tdbb)
+{
+	CountersLockHolder lockHolder(lockMutex);
+	if (!writer.entry_count && !readers.getCount())
+	{
+		LCK_release(tdbb, cached_lock);
+		invalidate(tdbb, false);
+		return true;
+	}
+		return false;
+	}
+
+} // namespace Jrd
diff --git a/src/jrd/GlobalRWLock.h b/src/jrd/GlobalRWLock.h
new file mode 100644
index 0000000000..ad524fea0e
--- /dev/null
+++ b/src/jrd/GlobalRWLock.h
@@ -0,0 +1,170 @@
+/*
+ *	PROGRAM:	JRD Access Method
+ *	MODULE:		GlobalRWLock.h
+ *	DESCRIPTION:	Cached Object Synchronizer
+ *
+ *  The contents of this file are subject to the Initial
+ *  Developer's Public License Version 1.0 (the "License");
+ *  you may not use this file except in compliance with the
+ *  License. You may obtain a copy of the License at
+ *  http://www.ibphoenix.com/main.nfs?a=ibphoenix&page=ibp_idpl.
+ *
+ *  Software distributed under the License is distributed AS IS,
+ *  WITHOUT WARRANTY OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing rights
+ *  and limitations under the License.
+ *
+ *  The Original Code was created by Nickolay Samofatov
+ *  for the Firebird Open Source RDBMS project.
+ *
+ *  Copyright (c) 2006 Nickolay Samofatov
+ *  and all contributors signed below.
+ *
+ *  All Rights Reserved.
+ *  Contributor(s): ______________________________________.
+ *
+ *
+ */
+
+#include "../common/classes/alloc.h"
+#include "../jrd/jrd.h"
+#include "../jrd/lck.h"
+#include "../jrd/lck_proto.h"
+#include "../include/fb_types.h"
+#include "../jrd/isc.h"
+
+//#define COS_DEBUG
+
+#ifdef COS_DEBUG
+DEFINE_TRACE_ROUTINE(cos_trace);
+#define COS_TRACE(args) cos_trace args
+#define COS_TRACE_AST(message) gds__trace(message)
+#else
+#define COS_TRACE(args) /* nothing */
+#define COS_TRACE_AST(message) /* nothing */
+#endif
+
+
+namespace Jrd {
+
+typedef USHORT locktype_t;
+
+struct ObjectOwnerData {
+	SLONG owner_handle;
+	ULONG entry_count;
+	static const SLONG& generate(const void* sender, const ObjectOwnerData& value) {
+		return value.owner_handle;
+	}
+	ObjectOwnerData() {
+		owner_handle = 0;
+		entry_count = 0;
+	}
+};
+
+/*
+ * Architecture goals for the class
+ * - Lock to protect intra-process cached resources with object-oriented interface:
+ *   invalidate()/fetch()
+ * - Two lock modes: LCK_read (LCK_PR) and LCK_write (LCK_EX)
+ * - Support for lock recursion (multiple acquires of a lock by a given owner)
+ * - Flexible execution environment
+ * - Multiple threads
+ * - Multiple processes
+ * - Signals
+ * - Locks belong to logical owners (typically type ATTACHMENT or DATABASE, but
+ *   potentially also THREAD and PROCESS)
+ * - Logical ownership of a lock may change during the object access lifecycle
+ *   (somewhat special case, happens if cached resource needs to be passed from
+ *   one worker thread to another without releasing the lock)
+ *
+ * Implementation constraints
+ * - Avoid calling lock manager for synchronization in non-contention case
+ *   (for performance reasons, especially in DLM environments)
+ * - All contention to be handled via Lock manager to ensure reliable deadlock
+ *   detection and to be monitored and debuggable via standard means
+ */
+class GlobalRWLock : public Firebird::PermanentStorage {
+public:
+	GlobalRWLock(thread_db* tdbb, MemoryPool& p, locktype_t lckType, 
+					   size_t lockLen, const UCHAR* lockStr,
+					   lck_owner_t physical_lock_owner = LCK_OWNER_database,
+					   lck_owner_t default_logical_lock_owner = LCK_OWNER_attachment,
+					   bool lock_caching = true);
+
+	virtual ~GlobalRWLock();
+
+	// As usual, 
+	// wait = 0 - try to lock a thing instantly (doesn't send ASTs)
+	// wait < 0 - timeout in seconds (doesn't deadlock)
+	// wait > 0 - infinite wait (may deadlock)
+	//
+	// This function returns false if it cannot take the lock
+	bool lock(thread_db* tdbb, locklevel_t level, SSHORT wait, SLONG owner_handle);
+	bool lock(thread_db* tdbb, locklevel_t level, SSHORT wait) {
+		return lock(tdbb, level, wait, LCK_get_owner_handle_by_type(tdbb, defaultLogicalLockOwner));
+	}
+
+	// NOTE: unlock method must be signal safe
+	// This function may be called in AST. The function doesn't wait.
+	void unlock(thread_db* tdbb, locklevel_t level, SLONG owner_handle);
+	void unlock(thread_db* tdbb, locklevel_t level) {
+		unlock(tdbb, level, LCK_get_owner_handle_by_type(tdbb, defaultLogicalLockOwner));
+	}
+
+	// Change the lock owner. The function doesn't wait.
+	void changeLockOwner(thread_db* tdbb, locklevel_t level, SLONG old_owner_handle, SLONG new_owner_handle);
+
+	SLONG getLockData() {
+		return cached_lock->lck_data;
+	}
+	void setLockData(SLONG lck_data);
+
+	// Release phisical lock if possible. Use to force refetch
+	// Returns true if lock was released
+	bool tryReleaseLock(thread_db* tdbb);
+protected:
+	Lock* cached_lock;
+	// Flag to indicate that somebody is waiting via lock manager.
+	// If somebody uses lock manager, all concurrent requests should also
+	// go via lock manager to prevent starvation.
+	int internal_blocking;
+	bool external_blocking; // Unprocessed AST pending
+
+	// Load the object from shared location.
+	virtual void fetch(thread_db* tdbb) {}
+
+	// May be called under AST. Should not throw exceptions.
+	virtual void invalidate(thread_db* tdbb, bool ast_handler) {}
+
+	virtual void blockingAstHandler(thread_db* tdbb);
+private:
+	Firebird::Mutex lockMutex;	// Protects status of logical lock, counters and blocking flag
+	lck_owner_t		physicalLockOwner;	// Holds cached lock
+	lck_owner_t		defaultLogicalLockOwner;	// Requests new lock to replace cached
+	
+	// true - unlock keep cached lock and release by AST. 
+	// false - unlock releases cached lock if possible
+	bool	lockCaching;
+
+	Firebird::SortedArray<ObjectOwnerData, Firebird::EmptyStorage<ObjectOwnerData>, 
+		SLONG, ObjectOwnerData, Firebird::DefaultComparator<SLONG> > readers;
+	ObjectOwnerData writer;
+
+	// In current implementation, threads are not used along with signals
+	// Anyways, if we own mutex only with signals disabled this code
+	// becomes signal-safe even in presense of threads.
+	//
+	// SUPERSERVER: We do not call any functions that can cause wait 
+	// when under counters lock so we do not need to release thread
+	// scheduler here
+	class CountersLockHolder : public AstInhibit, public Firebird::MutexLockGuard
+	{
+	public:
+		CountersLockHolder(Firebird::Mutex& mtx)
+			: AstInhibit(), MutexLockGuard(mtx) { }
+	};
+
+	static int blocking_ast_cached_lock(void* ast_object);
+};
+
+}