Reworked re-attaching the shared memory after its concurrent deletion

src/common/isc_s_proto.h

@@ -174,7 +174,10 @@ struct event_t
 class MemoryHeader
 {
 public:
-	static const USHORT HEADER_VERSION = 1;
+	static const USHORT HEADER_VERSION = 2;
+
+	// Values for mhb_flags
+	static const USHORT FLAG_DELETED = 1;	// Shared file has been deleted
 
 	void init(USHORT type, USHORT version)
 	{
@@ -182,15 +185,26 @@ public:
 		mhb_header_version = HEADER_VERSION;
 		mhb_version = version;
 		mhb_timestamp = TimeStamp::getCurrentTimeStamp().value();
+		mhb_flags = 0;
 #ifdef HAVE_SHARED_MUTEX_SECTION
 		fb_assert(sizeof(mhb_mutex) <= sizeof(dummy));
 #endif
 	}
 
+	void markAsDeleted()
+	{
+		mhb_flags |= FLAG_DELETED;
+	}
+
+	bool isDeleted() const
+	{
+		return (mhb_flags & FLAG_DELETED);
+	}
+
 	USHORT mhb_type;
 	USHORT mhb_header_version;
 	USHORT mhb_version;
-	USHORT reserve;					// not used
+	USHORT mhb_flags;
 	GDS_TIMESTAMP mhb_timestamp;
 	union
 	{
@@ -333,18 +347,6 @@ public:
 										  // because there is no portable barrier semantics for them. Only MS2005+ generate
 										  // barriers, and all other compilers generally do not.
 
-	bool justCreated()
-	{
-		if (sh_mem_just_created)
-		{
-			// complete initialization
-			sh_mem_just_created = false;
-			return true;
-		}
-
-		return false;
-	}
-
 private:
 #ifdef USE_SYS5SEMAPHORE
 	int		fileNum;	// file number in shared table of shared files
@@ -353,7 +355,6 @@ private:
 #endif
 
 	IpcObject* sh_mem_callback;
-	bool sh_mem_just_created;
 #ifdef WIN_NT
 	bool sh_mem_unlink;
 #endif

src/common/isc_sync.cpp

@@ -1734,11 +1734,15 @@ ULONG ISC_exception_post(ULONG except_code, const TEXT* err_msg, ISC_STATUS& isc
 
 void SharedMemoryBase::removeMapFile()
 {
+	fb_assert(sh_mem_header && !sh_mem_header->isDeleted());
+
 #ifndef WIN_NT
 	unlinkFile();
 #else
 	sh_mem_unlink = true;
 #endif // WIN_NT
+
+	sh_mem_header->markAsDeleted();
 }
 
 void SharedMemoryBase::unlinkFile()
@@ -1965,7 +1969,6 @@ SharedMemoryBase::SharedMemoryBase(const TEXT* filename, ULONG length, IpcObject
 		if (trunc_flag)
 			FB_UNUSED(os_utils::ftruncate(mainLock->getFd(), length));
 
-		sh_mem_just_created = true;
 		if (callback->initialize(this, true))
 		{
 #ifdef HAVE_SHARED_MUTEX_SECTION
@@ -2089,7 +2092,6 @@ SharedMemoryBase::SharedMemoryBase(const TEXT* filename, ULONG length, IpcObject
 	}
 	else
 	{
-		sh_mem_just_created = false;
 		if (callback->initialize(this, false))
 		{
 			if (!mainLock->setlock(&statusVector, FileLock::FLM_SHARED))
@@ -2419,7 +2421,6 @@ SharedMemoryBase::SharedMemoryBase(const TEXT* filename, ULONG length, IpcObject
 	sh_mem_hdr_address = header_address;
 	strcpy(sh_mem_name, filename);
 
-	sh_mem_just_created = init_flag;
 	sh_mem_callback->initialize(this, init_flag);
 
 	if (init_flag)

src/jrd/Monitoring.cpp

@@ -166,7 +166,7 @@ MonitoringData::MonitoringData(Database* dbb)
 
 MonitoringData::~MonitoringData()
 {
-	m_sharedMemory->mutexLock();
+	Guard guard(this);
 
 	try
 	{
@@ -178,8 +178,6 @@ MonitoringData::~MonitoringData()
 	}
 	catch (const Exception&)
 	{} // no-op
-
-	m_sharedMemory->mutexUnlock();
 }
 
 
@@ -210,12 +208,13 @@ void MonitoringData::acquire()
 	m_localMutex.enter(FB_FUNCTION);
 	m_sharedMemory->mutexLock();
 
-	while (m_sharedMemory->getHeader()->used == alignOffset(sizeof(Header)))
-	{
-		if (m_sharedMemory->justCreated())
-			break;
+	// Reattach if someone has just deleted the shared file
+
+	while (m_sharedMemory->getHeader()->isDeleted())
+	{
+		// Shared memory must be empty at this point
+		fb_assert(m_sharedMemory->getHeader()->used == alignOffset(sizeof(Header)));
 
-		// Someone is going to delete shared file? Reattach.
 		m_sharedMemory->mutexUnlock();
 		m_sharedMemory.reset();
 
@@ -225,8 +224,6 @@ void MonitoringData::acquire()
 		m_sharedMemory->mutexLock();
 	}
 
-	fb_assert(!m_sharedMemory->justCreated());
-
 	if (m_sharedMemory->getHeader()->allocated > m_sharedMemory->sh_mem_length_mapped)
 	{
 #ifdef HAVE_OBJECT_MAP

src/jrd/event.cpp

@@ -459,18 +459,17 @@ void EventManager::acquire_shmem()
 
 	m_sharedMemory->mutexLock();
 
-	// Check for shared memory state consistency
+	// Reattach if someone has just deleted the shared file
 
-	while (SRQ_EMPTY(m_sharedMemory->getHeader()->evh_processes))
+	while (m_sharedMemory->getHeader()->isDeleted())
 	{
 		fb_assert(!m_process);
 		if (m_process)
 			fb_utils::logAndDie("Process disappeared in EventManager::acquire_shmem");
 
-		if (m_sharedMemory->justCreated())
-			break;
+		// Shared memory must be empty at this point
+		fb_assert(SRQ_EMPTY(m_sharedMemory->getHeader()->evh_processes));
 
-		// Someone is going to delete shared file? Reattach.
 		m_sharedMemory->mutexUnlock();
 		m_sharedMemory.reset();
 
@@ -480,8 +479,6 @@ void EventManager::acquire_shmem()
 		m_sharedMemory->mutexLock();
 	}
 
-	fb_assert(!m_sharedMemory->justCreated());
-
 	m_sharedMemory->getHeader()->evh_current_process = m_processOffset;
 
 	if (m_sharedMemory->getHeader()->evh_length > m_sharedMemory->sh_mem_length_mapped)

src/jrd/replication/ChangeLog.cpp

@@ -402,27 +402,25 @@ void ChangeLog::lockState()
 	m_localMutex.enter(FB_FUNCTION);
 	m_sharedMemory->mutexLock();
 
+	// Reattach if someone has just deleted the shared file
+
+	while (m_sharedMemory->getHeader()->isDeleted())
+	{
+		// Shared memory must be empty at this point
+		fb_assert(!m_sharedMemory->getHeader()->pidLower);
+		fb_assert(!m_sharedMemory->getHeader()->pidUpper);
+
+		m_sharedMemory->mutexUnlock();
+		m_sharedMemory.reset();
+
+		Thread::yield();
+
+		initSharedFile();
+		m_sharedMemory->mutexLock();
+	}
+
 	try
 	{
-		while (!m_sharedMemory->getHeader()->pidUpper)
-		{
-			fb_assert(!m_sharedMemory->getHeader()->pidLower);
-
-			if (m_sharedMemory->justCreated())
-				break;
-
-			// Someone is going to delete shared file? Reattach.
-			m_sharedMemory->mutexUnlock();
-			m_sharedMemory.reset();
-
-			Thread::yield();
-
-			initSharedFile();
-			m_sharedMemory->mutexLock();
-		}
-
-		fb_assert(!m_sharedMemory->justCreated());
-
 		const auto state = m_sharedMemory->getHeader();
 
 		if (m_segments.isEmpty() || state->segmentCount > m_segments.getCount())

src/lock/lock.cpp

@@ -1061,22 +1061,20 @@ void LockManager::acquire_shmem(SRQ_PTR owner_offset)
 	if (!locked)
 		m_sharedMemory->mutexLock();
 
-	// Check for shared memory state consistency
+	// Reattach if someone has just deleted the shared file
 
-	while (SRQ_EMPTY(m_sharedMemory->getHeader()->lhb_processes))
+	while (m_sharedMemory->getHeader()->isDeleted())
 	{
 		fb_assert(!m_process);
 		if (m_process)
 			bug(NULL, "Process disappeared in LockManager::acquire_shmem");
 
-		if (m_sharedMemory->justCreated())
-		{
-			// no sense thinking about statistics now
-			m_blockage = false;
-			break;
-		}
+		// Shared memory must be empty at this point
+		fb_assert(SRQ_EMPTY(m_sharedMemory->getHeader()->lhb_processes));
+
+		// no sense thinking about statistics now
+		m_blockage = false;
 
-		// Someone is going to delete shared file? Reattach.
 		m_sharedMemory->mutexUnlock();
 		m_sharedMemory.reset();
 
@@ -1088,8 +1086,6 @@ void LockManager::acquire_shmem(SRQ_PTR owner_offset)
 		m_sharedMemory->mutexLock();
 	}
 
-	fb_assert(!m_sharedMemory->justCreated());
-
 	++(m_sharedMemory->getHeader()->lhb_acquires);
 	if (m_blockage)
 	{