windows-nt/Source/XPSP1/NT/inetsrv/iis/staxinc/export/rwnew.h

/*++
	
	rwnew.h

	This file defines several variations of Reader/Writer locks
	with different properties regarding handles used, and other 
	implementation details.

	Also defined are some variations of CRITICAL_SECTIONS which use
	fewer or no handles.

--*/



#ifndef	_RWNEW_H
#define	_RWNEW_H

#ifdef	_RW_IMPLEMENTATION_
#define	_RW_INTERFACE_ __declspec( dllexport ) 
#else
#define	_RW_INTERFACE_	__declspec( dllimport ) 
#endif

#pragma	warning( disable:4251 )
						
#include	<limits.h>
#include	"lockq.h"
#include	"rwintrnl.h"


class	_RW_INTERFACE_	CCritSection	{
private :

	//
	//	Handle of thread owning the lock !
	//
	HANDLE		m_hOwner ;

	//
	//	Count of Recursive Calls 
	//
	long	m_RecursionCount ;	

	//
	//	Count used to see who gets the lock next !
	//
	long	m_lock ;

	//
	//	Queue of waiting threads 
	//
	CSingleReleaseQueue		m_queue ;

	//
	//	Copying of these objects is not allowed !!!!
	//
	CCritSection( CCritSection& ) ;
	CCritSection&	operator=( CCritSection& ) ;

public : 

#ifdef	DEBUG
	DWORD	m_dwThreadOwner ;
#endif	

	//
	//	Construct a critical section object
	//
	CCritSection( ) :	
		m_queue( FALSE ),
		m_hOwner( INVALID_HANDLE_VALUE ), 
		m_RecursionCount( 0 ), 
		m_lock( -1 ) {
	}

	//
	//	Acquire the critical section
	//
	void	
	Enter(	
			CWaitingThread&	myself 
			) ;

	//
	//	Another version which acquires the critical section - 
	//	creates its own CWaitingThread object !
	//
	void	
	Enter() ;

	//
	//	REturns TRUE if the lock is available right now !
	//
	BOOL
	TryEnter(
			CWaitingThread&	myself 
			) ;

	//
	//	Returns TRUE if we can get the lock right now !
	//
	BOOL
	TryEnter()	{
		CWaitingThread	myself ;
		return	TryEnter( myself ) ;
	}

	//
	//	Release the critical section !
	//
	void
	Leave() ;

		
} ;


//
//	This version of critical section is more like an event - doesn't
//	care who releases locks - and doesn't handle recursive grabs !
//
class	_RW_INTERFACE_	CSimpleCritSection	{
private :

	//
	//	Count used to see who gets the lock next !
	//
	long	m_lock ;

	//
	//	Queue of waiting threads 
	//
	CSingleReleaseQueue		m_queue ;

	//
	//	Copying of these objects is not allowed !!!!
	//
	CSimpleCritSection( CCritSection& ) ;
	CSimpleCritSection&	operator=( CCritSection& ) ;

public : 

#ifdef	DEBUG
	DWORD	m_dwThreadOwner ;
#endif	

	//
	//	Construct a critical section object
	//
	CSimpleCritSection( ) :	
		m_queue( FALSE ),
#ifdef	DEBUG
		m_dwThreadOwner( 0 ),
#endif
		m_lock( -1 ) {
	}

	//
	//	Acquire the critical section
	//
	void	
	Enter(	
			CWaitingThread&	myself 
			) ;

	//
	//	Another version which acquires the critical section - 
	//	creates its own CWaitingThread object !
	//
	void	
	Enter() ;

	//
	//	REturns TRUE if the lock is available right now !
	//
	BOOL
	TryEnter(
			CWaitingThread&	myself 
			) ;

	//
	//	Returns TRUE if we can get the lock right now !
	//
	BOOL
	TryEnter()	{
		CWaitingThread	myself ;
		return	TryEnter( myself ) ;
	}

	//
	//	Release the critical section !
	//
	void
	Leave() ;
	
} ;

//
//	Another class which tries to create Reader/Write locks with
//	no handles !!
//

class	_RW_INTERFACE_	CShareLockNH	{
private : 

	//	
	//	Lock grabbed by writers to have exclusive access
	//
	CSimpleCritSection	m_lock ;

	//
	//	Number of readers who have grabbed the Read Lock - 
	//	Negative if a writer is waiting !
	//
	volatile	long	m_cReadLock ;

	//
	//	Number of Readers who have left the lock since a 
	//	writer tried to grab it !
	//
	volatile	long	m_cOutReaders ;

	//
	//	Number of readers who are entering the lock after 
	//	being blocked !!!
	//
	volatile	long	m_cOutAcquiringReaders ;

	//
	//	Number of threads needing m_lock to be held right now !
	//
	volatile	long	m_cExclusiveRefs ;

	//
	//	Handle that all the readers who are waiting try to grab !
	//
	volatile	HANDLE	m_hWaitingReaders ;

	//
	//	Handle that the single writer waiting for the lock is trying
	//	to grab !
	//
	volatile	HANDLE	m_hWaitingWriters ;

	void	inline
	WakeReaders() ;

	//
	//	The internal work of ShareLock - does a lot more of the stuff required
	//	when a writer is present !!!
	//
	void
	ShareLockInternal() ;

	//
	//	The internal work of ShareLock - does a lot more of the stuff required
	//	when a writer is present !!!
	//
	void
	ShareUnlockInternal() ;
	

	//
	//	You may not copy these objects - so this lock is private !
	//
	CShareLockNH( CShareLockNH& ) ;

	//
	//	You may not copy through assignment - so this operator is private !
	//
	CShareLockNH&	operator=( CShareLockNH& ) ;
	
public : 

	//
	//	Construction of CShareLockNH() objects always succeeds and there
	//	are no error cases !
	//
	CShareLockNH() ;

	//
	//	Grab the lock Shared - other threads may pass through ShareLock() as well
	//
	void	ShareLock() ;

	//
	//	Releases the lock - if we are the last reader to leave writers may
	//	start to enter the lock !
	//
	void	ShareUnlock() ;

	//
	//	Grab the lock Exclusively - no other readers or writers may enter !!
	//
	void	ExclusiveLock() ;

	//
	//	Release the Exclusive Locks - if there are readers waiting they 
	//	will enter before other waiting writers !
	//
	void	ExclusiveUnlock() ;

	//
	//	Convert an ExclusiveLock to a Shared - this cannot fail !
	//
	void	ExclusiveToShared() ;

	//
	//	Convert a Shared Lock to an Exclusive one - this can fail - returns
	//	TRUE if successfull !
	//
	BOOL	SharedToExclusive() ;

	//
	//	Return TRUE if we can get the lock shared.  Only fails when 
	//	somebody is attempting or has the lock exclusively, we will enter
	//	if there are only other readers in the lock.
	//
	BOOL	TryShareLock() ;

	//
	//	Return TRUE if we can get the lock Exclusively.  Only succeeds
	//	when nobody else is near the lock.
	//
	BOOL	TryExclusiveLock() ;

	//
	//	PartialLocks - 
	//
	//	Partial Locks are similar to Exclusive Locks - only one thread
	//	can successfully call PartialLock(), any other threads calling
	//	PartialLock() or ExclusiveLock() will block.
	//	HOWEVER - while a PartialLock() is held, Readers (threads calling
	//	ShareLock()) may enter the lock.
	//
	void	PartialLock() ;

	//
	//	Release the PartialLock - Other Exclusive() or Partial lock acquirers
	//	may now enter.
	//
	void	PartialUnlock() ;

	//
	//	Convert a Partial Lock to an Exclusive Lock.  This function is 
	//	guaranteed to succeed, HOWEVER a lock can only be converted with 
	//	this function once, i.e. a thread doing
	//		PartialLock() ;
	//		FirstPartialToExclusive() ;
	//		ExclusiveToPartial() ;
	//		FirstPartialToExclusive() ;
	//	will have problems - the second call to FirstPartialToExclusive()
	//	may mess up the lock state and cause the lock to fail horribly.
	//	If a user wishes to convert as above they must have a call sequence like : 
	//
	//		PartialLock() ;
	//		FirstPartialToExclusive() or PartialToExclusive() ;
	//		ExclusiveToPartial() ;
	//		PartialToExclusive() ;
	//
	//	If you change lock states more than once - you take your chances !
	//
	void	FirstPartialToExclusive() ;

	//
	//	Returns TRUE if we can get the lock Exclusively, otherwise
	//	we return FALSE with the lock remaining in the Partially held state.
	//
	//	NOTE : NYI in CShareLockNH - will always return FALSE !
	//
	BOOL	PartialToExclusive() ;

	//
	//	We can always go from an ExclusiveLock() to a PartialLock() state.
	//
	void	ExclusiveToPartial() ;

	//
	//	We can always go from a PartialLock() state to a SharedLock() state
	//
	void	PartialToShared() ;

	//
	//	Returns TRUE if we can get the lock Partially !
	//	If it returns FALSE we remain with the lock held Shared()
	//
	BOOL	SharedToPartial() ;

	//
	//	Returns TRUE only if no other threads are trying to get the lock
	//	ExclusiveLy or Partially !
	//
	BOOL	TryPartialLock() ;

} ;

//
//  This is a utility function to get an Event Handle we save 
//  for each thread - the handle is Created as: 
//      CreateEvent( NULL, 
//                  FALSE, 
//                  FALSE,
//                  NULL ) ;
//  This results in an auto-reset event which goes back to non signalled whenever a thread
//  is released.
//
HANDLE
_RW_INTERFACE_
GetPerThreadEvent() ;



#endif	//	_RWNEW_H_