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/*++
Copyright (c) 1998-2000 Microsoft Corporation
Module Name :
locks.h
Abstract:
A collection of locks for multithreaded access to data structures
Author:
George V. Reilly (GeorgeRe) 06-Jan-1998
Environment:
Win32 - User Mode
Project:
Internet Information Server RunTime Library
Revision History:
--*/
#ifndef __LOCKS_H__
#define __LOCKS_H__
//--------------------------------------------------------------------
// File: locks.h
//
// A collection of different implementations of read/write locks that all
// share the same interface. This allows different locks to be plugged
// into C++ templates as parameters.
//
// The implementations are:
// CSmallSpinLock lightweight critical section
// CSpinLock variant of CSmallSpinLock
// CFakeLock do-nothing class; useful as a template parameter
// CCritSec Win32 CRITICAL_SECTION
// Multi-Reader/Single-Writer locks:
// CReaderWriterLock MRSW lock from Neel Jain
// CReaderWriterLock2 smaller implementation of CReaderWriterLock
// CReaderWriterLock3 CReaderWriterLock2 with recursive WriteLock
//
// CAutoReadLock<Lock> and CAutoWriteLock<Lock> can used as
// exception-safe wrappers.
//
// TODO:
// * Add a timeout feature to Try{Read,Write}Lock
// * Add some way of tracking all the owners of a multi-reader lock
//--------------------------------------------------------------------
#ifndef __IRTLDBG_H__
# include <irtldbg.h>
#endif
#ifdef __LOCKS_NAMESPACE__
namespace Locks {
#endif // __LOCKS_NAMESPACE__
enum LOCK_LOCKTYPE {
LOCK_SMALLSPINLOCK = 1,
LOCK_SPINLOCK,
LOCK_FAKELOCK,
LOCK_CRITSEC,
LOCK_READERWRITERLOCK,
LOCK_READERWRITERLOCK2,
LOCK_READERWRITERLOCK3,
};
// Forward declarations
class IRTL_DLLEXP CSmallSpinLock;
class IRTL_DLLEXP CSpinLock;
class IRTL_DLLEXP CFakeLock;
class IRTL_DLLEXP CCritSec;
class IRTL_DLLEXP CReaderWriterLock;
class IRTL_DLLEXP CReaderWriterLock2;
class IRTL_DLLEXP CReaderWriterLock3;
#if defined(_MSC_VER) && (_MSC_VER >= 1200)
// __forceinline keyword new to VC6
# define LOCK_FORCEINLINE __forceinline
#else
# define LOCK_FORCEINLINE inline
#endif
#ifdef _M_IX86
// The compiler will warn that the assembly language versions of the
// Lock_Atomic* functions don't return a value. Actually, they do: in EAX.
# pragma warning(disable: 4035)
#endif
// Workarounds for certain useful interlocked operations that are not
// available on Windows 95. Note: the CMPXCHG and XADD instructions were
// introduced in the 80486. If you still need to run on a 386 (unlikely in
// 2000), you'll need to use something else.
LOCK_FORCEINLINE
LONG
Lock_AtomicIncrement(
IN OUT PLONG plAddend)
{
#ifdef _M_IX86
__asm
{
mov ecx, plAddend
mov eax, 1
lock xadd [ecx], eax
inc eax // correct result
}
#else
return InterlockedIncrement(plAddend);
#endif
}
LOCK_FORCEINLINE
LONG
Lock_AtomicDecrement(
IN OUT PLONG plAddend)
{
#ifdef _M_IX86
__asm
{
mov ecx, plAddend
mov eax, -1
lock xadd [ecx], eax
dec eax // correct result
}
#else
return InterlockedDecrement(plAddend);
#endif
}
LOCK_FORCEINLINE
LONG
Lock_AtomicExchange(
IN OUT PLONG plAddr,
IN LONG lNew)
{
#ifdef _M_IX86
__asm
{
mov ecx, plAddr
mov edx, lNew
mov eax, [ecx]
LAEloop:
lock cmpxchg [ecx], edx
jnz LAEloop
}
#else
return InterlockedExchange(plAddr, lNew);
#endif
}
LOCK_FORCEINLINE
LONG
Lock_AtomicCompareExchange(
IN OUT PLONG plAddr,
IN LONG lNew,
IN LONG lCurrent)
{
#ifdef _M_IX86
__asm
{
mov ecx, plAddr
mov edx, lNew
mov eax, lCurrent
lock cmpxchg [ecx], edx
}
#else
return InterlockedCompareExchange(plAddr, lNew, lCurrent);
#endif
}
LOCK_FORCEINLINE
LONG
Lock_AtomicExchangeAdd(
IN OUT LPLONG plAddr,
IN LONG lValue)
{
#ifdef _M_IX86
__asm
{
mov ecx, plAddr
mov eax, lValue
lock xadd [ecx], eax
}
#else
return InterlockedExchangeAdd(plAddr, lValue);
#endif
}
#ifdef _M_IX86
# pragma warning(default: 4035)
// Makes tight loops a little more cache friendly and reduces power
// consumption. Needed on Willamette processors.
# define Lock_Yield() _asm { rep nop }
#else
# define Lock_Yield() ((void) 0)
#endif
//--------------------------------------------------------------------
// Spin count values.
enum LOCK_SPINS {
LOCK_MAXIMUM_SPINS = 10000, // maximum allowable spin count
LOCK_DEFAULT_SPINS = 4000, // default spin count
LOCK_MINIMUM_SPINS = 100, // minimum allowable spin count
LOCK_USE_DEFAULT_SPINS = 0xFFFF, // use class default spin count
LOCK_DONT_SPIN = 0, // don't spin at all
};
// Boilerplate code for the per-class default spincount and spinfactor
#define LOCK_DEFAULT_SPIN_IMPLEMENTATION() \
protected: \
/* per-class variables */ \
static WORD sm_wDefaultSpinCount; /* global default spin count */ \
static double sm_dblDfltSpinAdjFctr; /* global spin adjustment factor*/\
\
public: \
/* Set the default spin count for all locks */ \
static void SetDefaultSpinCount(WORD wSpins) \
{ \
IRTLASSERT((wSpins == LOCK_DONT_SPIN) \
|| (wSpins == LOCK_USE_DEFAULT_SPINS) \
|| (LOCK_MINIMUM_SPINS <= wSpins \
&& wSpins <= LOCK_MAXIMUM_SPINS)); \
\
if ((LOCK_MINIMUM_SPINS <= wSpins && wSpins <= LOCK_MAXIMUM_SPINS)\
|| (wSpins == LOCK_DONT_SPIN)) \
sm_wDefaultSpinCount = wSpins; \
else if (wSpins == LOCK_USE_DEFAULT_SPINS) \
sm_wDefaultSpinCount = LOCK_DEFAULT_SPINS; \
} \
\
/* Return the default spin count for all locks */ \
static WORD GetDefaultSpinCount() \
{ \
return sm_wDefaultSpinCount; \
} \
\
/* Set the adjustment factor for the spincount, used in each iteration */\
/* of countdown-and-sleep by the backoff algorithm. */ \
static void SetDefaultSpinAdjustmentFactor(double dblAdjFactor) \
{ \
IRTLASSERT(0.1 <= dblAdjFactor && dblAdjFactor <= 10.0); \
if (0.1 <= dblAdjFactor && dblAdjFactor <= 10.0) \
sm_dblDfltSpinAdjFctr = dblAdjFactor; \
} \
\
/* Return the default spin count for all locks */ \
static double GetDefaultSpinAdjustmentFactor() \
{ \
return sm_dblDfltSpinAdjFctr; \
} \
//--------------------------------------------------------------------
// Various Lock Traits
// Is the lock a simple mutex or a multi-reader/single-writer lock?
enum LOCK_RW_MUTEX {
LOCK_MUTEX = 1, // mutexes allow only one thread to hold the lock
LOCK_MRSW, // multi-reader, single-writer
};
// Can the lock be recursively acquired?
enum LOCK_RECURSION {
LOCK_RECURSIVE = 1, // Write and Read locks can be recursively acquired
LOCK_READ_RECURSIVE, // Read locks can be reacquired, but not Write
LOCK_NON_RECURSIVE, // Will deadlock if attempt to acquire recursively
};
// Does the lock Sleep in a loop or block on a kernel synch object handle?
// May (or may not) spin first before sleeping/blocking.
enum LOCK_WAIT_TYPE {
LOCK_WAIT_SLEEP = 1, // Calls Sleep() in a loop
LOCK_WAIT_HANDLE, // Blocks on a kernel mutex, semaphore, or event
};
// When the lock is taken, how are the waiters dequeued?
enum LOCK_QUEUE_TYPE {
LOCK_QUEUE_FIFO = 1, // First in, first out. Fair.
LOCK_QUEUE_LIFO, // Unfair but CPU cache friendly
LOCK_QUEUE_KERNEL, // Determined by vagaries of scheduler
};
// Can the lock's spincount be set on a per-lock basis, or is it only
// possible to modify the default spincount for all the locks in this class?
enum LOCK_PERLOCK_SPIN {
LOCK_NO_SPIN = 1, // The locks do not spin at all
LOCK_CLASS_SPIN, // Can set class-wide spincount, not individual
LOCK_INDIVIDUAL_SPIN, // Can set a spincount on an individual lock
};
//--------------------------------------------------------------------
// CLockBase: bundle the above attributes
template < LOCK_LOCKTYPE locktype,
LOCK_RW_MUTEX mutextype,
LOCK_RECURSION recursiontype,
LOCK_WAIT_TYPE waittype,
LOCK_QUEUE_TYPE queuetype,
LOCK_PERLOCK_SPIN spintype
>
class CLockBase
{
public:
static LOCK_LOCKTYPE LockType() {return locktype;}
static LOCK_RW_MUTEX MutexType() {return mutextype;}
static LOCK_RECURSION Recursion() {return recursiontype;}
static LOCK_WAIT_TYPE WaitType() {return waittype;}
static LOCK_QUEUE_TYPE QueueType() {return queuetype;}
static LOCK_PERLOCK_SPIN PerLockSpin() {return spintype;}
};
// Lock instrumentation causes all sorts of interesting statistics about
// lock contention, etc., to be gathered, but makes locks considerably fatter
// and somewhat slower. Turned off by default.
// #define LOCK_INSTRUMENTATION 1
#ifdef LOCK_INSTRUMENTATION
// We generally don't want to instrument CSmallSpinLock in addition
// to CSpinLock1, as it makes a CSpinLock1 huge.
// #define LOCK_SMALL_SPIN_INSTRUMENTATION 1
//--------------------------------------------------------------------
// CLockStatistics: statistics for an individual lock
class IRTL_DLLEXP CLockStatistics
{
public:
enum {
L_NAMELEN = 8,
};
double m_nContentions; // #times this lock was already locked
double m_nSleeps; // Total #Sleep()s needed
double m_nContentionSpins; // Total iterations this lock spun
double m_nAverageSpins; // Average spins each contention needed
double m_nReadLocks; // Number of times lock acquired for reading
double m_nWriteLocks; // Number of times lock acquired for writing
char m_szName[L_NAMELEN];// Name of this lock
CLockStatistics()
: m_nContentions(0),
m_nSleeps(0),
m_nContentionSpins(0),
m_nAverageSpins(0),
m_nReadLocks(0),
m_nWriteLocks(0)
{
m_szName[0] = '\0';
}
};
//--------------------------------------------------------------------
// CGlobalLockStatistics: statistics for all the known locks
class IRTL_DLLEXP CGlobalLockStatistics
{
public:
LONG m_cTotalLocks; // Total number of locks created
LONG m_cContendedLocks; // Total number of contended locks
LONG m_nSleeps; // Total #Sleep()s needed by all locks
LONGLONG m_cTotalSpins; // Total iterations all locks spun
double m_nAverageSpins; // Average spins needed for each contended lock
LONG m_nReadLocks; // Total ReadLocks
LONG m_nWriteLocks; // Total WriteLocks
CGlobalLockStatistics()
: m_cTotalLocks(0),
m_cContendedLocks(0),
m_nSleeps(0),
m_cTotalSpins(0),
m_nAverageSpins(0),
m_nReadLocks(0),
m_nWriteLocks(0)
{}
};
# define LOCK_INSTRUMENTATION_DECL() \
private: \
volatile LONG m_nContentionSpins; /* #iterations this lock spun */ \
volatile WORD m_nContentions; /* #times lock was already locked */\
volatile WORD m_nSleeps; /* #Sleep()s needed */ \
volatile WORD m_nReadLocks; /* #ReadLocks */ \
volatile WORD m_nWriteLocks; /* #WriteLocks */ \
char m_szName[CLockStatistics::L_NAMELEN]; /* Name of lock */\
\
static LONG sm_cTotalLocks; /* Total number of locks created */ \
static LONG sm_cContendedLocks; /* Total number of contended locks */\
static LONG sm_nSleeps; /* Total #Sleep()s by all locks */ \
static LONGLONG sm_cTotalSpins; /* Total iterations all locks spun */\
static LONG sm_nReadLocks; /* Total ReadLocks */ \
static LONG sm_nWriteLocks; /* Total WriteLocks */ \
\
public: \
const char* Name() const {return m_szName;} \
\
CLockStatistics Statistics() const; \
static CGlobalLockStatistics GlobalStatistics(); \
static void ResetGlobalStatistics(); \
private: \
// Add this to constructors
# define LOCK_INSTRUMENTATION_INIT(pszName) \
m_nContentionSpins = 0; \
m_nContentions = 0; \
m_nSleeps = 0; \
m_nReadLocks = 0; \
m_nWriteLocks = 0; \
++sm_cTotalLocks; \
if (pszName == NULL) \
m_szName[0] = '\0'; \
else \
strncpy(m_szName, pszName, sizeof(m_szName))
// Note: we are not using Interlocked operations for the shared
// statistical counters. We'll lose perfect accuracy, but we'll
// gain by reduced bus synchronization traffic.
# define LOCK_READLOCK_INSTRUMENTATION() \
{ ++m_nReadLocks; \
++sm_nReadLocks; }
# define LOCK_WRITELOCK_INSTRUMENTATION() \
{ ++m_nWriteLocks; \
++sm_nWriteLocks; }
#else // !LOCK_INSTRUMENTATION
# define LOCK_INSTRUMENTATION_DECL()
# define LOCK_READLOCK_INSTRUMENTATION() ((void) 0)
# define LOCK_WRITELOCK_INSTRUMENTATION() ((void) 0)
#endif // !LOCK_INSTRUMENTATION
//--------------------------------------------------------------------
// CAutoReadLock<Lock> and CAutoWriteLock<Lock> provide exception-safe
// acquisition and release of the other locks defined below
template <class _Lock>
class IRTL_DLLEXP CAutoReadLock
{
private:
bool m_fLocked;
_Lock& m_Lock;
public:
CAutoReadLock(
_Lock& rLock,
bool fLockNow = true)
: m_fLocked(false), m_Lock(rLock)
{
if (fLockNow)
Lock();
}
~CAutoReadLock()
{
Unlock();
}
void Lock()
{
// disallow recursive acquisition of the lock through this wrapper
if (!m_fLocked)
{
m_fLocked = true;
m_Lock.ReadLock();
}
}
void Unlock()
{
if (m_fLocked)
{
m_Lock.ReadUnlock();
m_fLocked = false;
}
}
};
template <class _Lock>
class IRTL_DLLEXP CAutoWriteLock
{
private:
bool m_fLocked;
_Lock& m_Lock;
public:
CAutoWriteLock(
_Lock& rLock,
bool fLockNow = true)
: m_fLocked(false), m_Lock(rLock)
{
if (fLockNow)
Lock();
}
~CAutoWriteLock()
{
Unlock();
}
void Lock()
{
// disallow recursive acquisition of the lock through this wrapper
if (!m_fLocked)
{
m_fLocked = true;
m_Lock.WriteLock();
}
}
void Unlock()
{
if (m_fLocked)
{
m_fLocked = false;
m_Lock.WriteUnlock();
}
}
};
//--------------------------------------------------------------------
// A spinlock is a sort of lightweight critical section. Its main
// advantage over a true Win32 CRITICAL_SECTION is that it occupies 4 bytes
// instead of 24 (+ another 32 bytes for the RTL_CRITICAL_SECTION_DEBUG data),
// which is important when we have many thousands of locks
// and we're trying to be L1 cache-conscious. A CRITICAL_SECTION also
// contains a HANDLE to a semaphore, although this is not initialized until
// the first time that the CRITICAL_SECTION blocks.
//
// On a multiprocessor machine, a spinlock tries to acquire the lock. If
// it fails, it sits in a tight loop, testing the lock and decrementing a
// counter. If the counter reaches zero, it does a Sleep(0), yielding the
// processor to another thread. When control returns to the thread, the
// lock is probably free. If not, the loop starts again and it is
// terminated only when the lock is acquired. The theory is that it is
// less costly to spin in a busy loop for a short time rather than
// immediately yielding the processor, forcing an expensive context switch
// that requires the old thread's state (registers, etc) be saved, the new
// thread's state be reloaded, and the L1 and L2 caches be left full of
// stale data.
//
// You can tune the spin count (global only: per-lock spin counts are
// disabled) and the backoff algorithm (the factor by which the spin
// count is multiplied after each Sleep).
//
// On a 1P machine, the loop is pointless---this thread has control,
// hence no other thread can possibly release the lock while this thread
// is looping---so the processor is yielded immediately.
//
// The kernel uses spinlocks internally and spinlocks were also added to
// CRITICAL_SECTIONs in NT 4.0 sp3. In the CRITICAL_SECTION implementation,
// however, the counter counts down only once and waits on a semaphore
// thereafter (i.e., the same blocking behavior that it exhibits without
// the spinlock).
//
// A disadvantage of a user-level spinlock such as this is that if the
// thread that owns the spinlock blocks for any reason (or is preempted by
// the scheduler), all the other threads will continue to spin on the
// spinlock, wasting CPU, until the owning thread completes its wait and
// releases the lock. (The kernel spinlocks, however, are smart enough to
// switch to another runnable thread instead of wasting time spinning.)
// The backoff algorithm decreases the spin count on each iteration in an
// attempt to minimize this effect. The best policy---and this is true for
// all locks---is to hold the lock for as short as time as possible.
//
// Note: unlike a CRITICAL_SECTION, a CSmallSpinLock cannot be recursively
// acquired; i.e., if you acquire a spinlock and then attempt to acquire it
// again *on the same thread* (perhaps from a different function), the
// thread will hang forever. Use CSpinLock instead, which is safe though a
// little slower than a CSmallSpinLock. If you own all the code
// that is bracketed by Lock() and Unlock() (e.g., no callbacks or passing
// back of locked data structures to callers) and know for certain that it
// will not attempt to reacquire the lock, you can use CSmallSpinLock.
//
// See also http://muralik/work/performance/spinlocks.htm and John Vert's
// MSDN article, "Writing Scalable Applications for Windows NT".
//
// The original implementation is due to PALarson.
class IRTL_DLLEXP CSmallSpinLock :
public CLockBase<LOCK_SMALLSPINLOCK, LOCK_MUTEX,
LOCK_NON_RECURSIVE, LOCK_WAIT_SLEEP, LOCK_QUEUE_KERNEL,
LOCK_CLASS_SPIN
>
{
private:
volatile LONG m_lTid; // The lock state variable
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_INSTRUMENTATION_DECL();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_FORCEINLINE static LONG _CurrentThreadId()
{
DWORD dwTid = ::GetCurrentThreadId();
return (LONG) (dwTid);
}
private:
// Does all the spinning (and instrumentation) if the lock is contended.
void _LockSpin();
LOCK_FORCEINLINE bool _TryLock()
{
if (m_lTid == 0)
{
LONG l = _CurrentThreadId();
return (Lock_AtomicCompareExchange(const_cast<LONG*>(&m_lTid), l,0)
== 0);
}
else
return false;
}
public:
#ifndef LOCK_SMALL_SPIN_INSTRUMENTATION
CSmallSpinLock()
: m_lTid(0)
{}
#else // LOCK_SMALL_SPIN_INSTRUMENTATION
CSmallSpinLock(
const char* pszName)
: m_lTid(0)
{
LOCK_INSTRUMENTATION_INIT(pszName);
}
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
#ifdef _DEBUG
~CSmallSpinLock()
{
IRTLASSERT(m_lTid == 0);
}
#endif // _DEBUG
// Acquire an exclusive lock for writing. Blocks until acquired.
inline void WriteLock()
{
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_WRITELOCK_INSTRUMENTATION();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
// Optimize for the common case by helping the processor's branch
// prediction algorithm.
if (_TryLock())
return;
_LockSpin();
}
// Acquire a (possibly shared) lock for reading. Blocks until acquired.
inline void ReadLock()
{
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_READLOCK_INSTRUMENTATION();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
if (_TryLock())
return;
_LockSpin();
}
// Try to acquire an exclusive lock for writing. Returns true
// if successful. Non-blocking.
inline bool TryWriteLock()
{
bool fAcquired = _TryLock();
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
if (fAcquired)
LOCK_WRITELOCK_INSTRUMENTATION();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
return fAcquired;
}
// Try to acquire a (possibly shared) lock for reading. Returns true
// if successful. Non-blocking.
inline bool TryReadLock()
{
bool fAcquired = _TryLock();
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
if (fAcquired)
LOCK_READLOCK_INSTRUMENTATION();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
return fAcquired;
}
// Unlock the lock after a successful call to {,Try}WriteLock().
// Assumes caller owned the lock.
inline void WriteUnlock()
{
Lock_AtomicExchange(const_cast<LONG*>(&m_lTid), 0);
}
// Unlock the lock after a successful call to {,Try}ReadLock().
// Assumes caller owned the lock.
inline void ReadUnlock()
{
WriteUnlock();
}
// Is the lock already locked for writing by this thread?
bool IsWriteLocked() const
{
return (m_lTid == _CurrentThreadId());
}
// Is the lock already locked for reading?
bool IsReadLocked() const
{
return IsWriteLocked();
}
// Is the lock unlocked for writing?
bool IsWriteUnlocked() const
{
return (m_lTid == 0);
}
// Is the lock unlocked for reading?
bool IsReadUnlocked() const
{
return IsWriteUnlocked();
}
// Convert a reader lock to a writer lock
void ConvertSharedToExclusive()
{
// no-op
}
// Convert a writer lock to a reader lock
void ConvertExclusiveToShared()
{
// no-op
}
// Set the spin count for this lock.
// Returns true if successfully set the per-lock spincount, false otherwise
bool SetSpinCount(WORD wSpins)
{
IRTLASSERT((wSpins == LOCK_DONT_SPIN)
|| (wSpins == LOCK_USE_DEFAULT_SPINS)
|| (LOCK_MINIMUM_SPINS <= wSpins
&& wSpins <= LOCK_MAXIMUM_SPINS));
return false;
}
// Return the spin count for this lock.
WORD GetSpinCount() const
{
return sm_wDefaultSpinCount;
}
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CSmallSpinLock";}
}; // CSmallSpinLock
//--------------------------------------------------------------------
// CSpinLock is a spinlock that doesn't deadlock if recursively acquired.
// This version occupies only 4 bytes. Uses 28 bits for the thread id.
class IRTL_DLLEXP CSpinLock :
public CLockBase<LOCK_SPINLOCK, LOCK_MUTEX,
LOCK_RECURSIVE, LOCK_WAIT_SLEEP, LOCK_QUEUE_KERNEL,
LOCK_CLASS_SPIN
>
{
private:
// a union for convenience
volatile LONG m_lTid;
enum {
THREAD_SHIFT = 0,
THREAD_BITS = 28,
OWNER_SHIFT = THREAD_BITS,
OWNER_BITS = 4,
THREAD_MASK = ((1 << THREAD_BITS) - 1) << THREAD_SHIFT,
OWNER_INCR = 1 << THREAD_BITS,
OWNER_MASK = ((1 << OWNER_BITS) - 1) << OWNER_SHIFT,
};
LOCK_INSTRUMENTATION_DECL();
private:
// Get the current thread ID. Assumes that it can fit into 28 bits,
// which is fairly safe as NT recycles thread IDs and failing to fit into
// 28 bits would mean that more than 268,435,456 threads were currently
// active. This is improbable in the extreme as NT runs out of
// resources if there are more than a few thousands threads in
// existence and the overhead of context swapping becomes unbearable.
LOCK_FORCEINLINE static LONG _CurrentThreadId()
{
DWORD dwTid = ::GetCurrentThreadId();
// Thread ID 0 is used by the System Process (Process ID 0).
// We use a thread-id of zero to indicate that the lock is unowned.
// NT uses +ve thread ids, Win9x uses -ve ids
IRTLASSERT(dwTid != 0
&& ((dwTid <= THREAD_MASK) || (dwTid > ~THREAD_MASK)));
return (LONG) (dwTid & THREAD_MASK);
}
// Attempt to acquire the lock without blocking
LOCK_FORCEINLINE bool _TryLock()
{
if (m_lTid == 0)
{
LONG l = _CurrentThreadId() | OWNER_INCR;
return (Lock_AtomicCompareExchange(const_cast<LONG*>(&m_lTid), l,0)
== 0);
}
else
return false;
}
// Acquire the lock, recursively if need be
void _Lock()
{
// Do we own the lock already? Just bump the count.
if ((m_lTid & THREAD_MASK) == _CurrentThreadId())
{
// owner count isn't maxed out?
IRTLASSERT((m_lTid & OWNER_MASK) != OWNER_MASK);
Lock_AtomicExchangeAdd(const_cast<LONG*>(&m_lTid), OWNER_INCR);
}
// Some other thread owns the lock. We'll have to spin :-(.
else
_LockSpin();
IRTLASSERT((m_lTid & OWNER_MASK) > 0
&& (m_lTid & THREAD_MASK) == _CurrentThreadId());
}
// Release the lock
LOCK_FORCEINLINE void _Unlock()
{
IRTLASSERT((m_lTid & OWNER_MASK) > 0
&& (m_lTid & THREAD_MASK) == _CurrentThreadId());
LONG l = m_lTid - OWNER_INCR;
// Last owner? Release completely, if so
if ((l & OWNER_MASK) == 0)
l = 0;
Lock_AtomicExchange(const_cast<LONG*>(&m_lTid), l);
}
// Return true if the lock is owned by this thread
bool _IsLocked() const
{
bool fLocked = ((m_lTid & THREAD_MASK) == _CurrentThreadId());
IRTLASSERT(!fLocked || ((m_lTid & OWNER_MASK) > 0
&& (m_lTid & THREAD_MASK)==_CurrentThreadId()));
return fLocked;
}
// Does all the spinning (and instrumentation) if the lock is contended.
void _LockSpin();
public:
#ifndef LOCK_INSTRUMENTATION
CSpinLock()
: m_lTid(0)
{}
#else // LOCK_INSTRUMENTATION
CSpinLock(
const char* pszName)
: m_lTid(0)
{
LOCK_INSTRUMENTATION_INIT(pszName);
}
#endif // LOCK_INSTRUMENTATION
#ifdef _DEBUG
~CSpinLock()
{
IRTLASSERT(m_lTid == 0);
}
#endif // _DEBUG
// Acquire an exclusive lock for writing. Blocks until acquired.
inline void WriteLock()
{
LOCK_WRITELOCK_INSTRUMENTATION();
// Is the lock unowned?
if (_TryLock())
return; // got the lock
_Lock();
}
// Acquire a (possibly shared) lock for reading. Blocks until acquired.
inline void ReadLock()
{
LOCK_READLOCK_INSTRUMENTATION();
// Is the lock unowned?
if (_TryLock())
return; // got the lock
_Lock();
}
// See the description under CReaderWriterLock3::ReadOrWriteLock
inline bool ReadOrWriteLock()
{
ReadLock();
return true;
}
// Try to acquire an exclusive lock for writing. Returns true
// if successful. Non-blocking.
inline bool TryWriteLock()
{
bool fAcquired = _TryLock();
if (fAcquired)
LOCK_WRITELOCK_INSTRUMENTATION();
return fAcquired;
}
// Try to acquire a (possibly shared) lock for reading. Returns true
// if successful. Non-blocking.
inline bool TryReadLock()
{
bool fAcquired = _TryLock();
if (fAcquired)
LOCK_READLOCK_INSTRUMENTATION();
return fAcquired;
}
// Unlock the lock after a successful call to {,Try}WriteLock().
inline void WriteUnlock()
{
_Unlock();
}
// Unlock the lock after a successful call to {,Try}ReadLock().
inline void ReadUnlock()
{
_Unlock();
}
// Unlock the lock after a call to ReadOrWriteLock().
inline void ReadOrWriteUnlock(bool)
{
ReadUnlock();
}
// Is the lock already locked for writing?
bool IsWriteLocked() const
{
return _IsLocked();
}
// Is the lock already locked for reading?
bool IsReadLocked() const
{
return _IsLocked();
}
// Is the lock unlocked for writing?
bool IsWriteUnlocked() const
{
return !IsWriteLocked();
}
// Is the lock unlocked for reading?
bool IsReadUnlocked() const
{
return !IsReadLocked();
}
// Convert a reader lock to a writer lock
void ConvertSharedToExclusive()
{
// no-op
}
// Convert a writer lock to a reader lock
void ConvertExclusiveToShared()
{
// no-op
}
// Set the spin count for this lock.
bool SetSpinCount(WORD dwSpins) {return false;}
// Return the spin count for this lock.
WORD GetSpinCount() const
{
return sm_wDefaultSpinCount;
}
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CSpinLock";}
}; // CSpinLock
//--------------------------------------------------------------------
// A dummy class, primarily useful as a template parameter
class IRTL_DLLEXP CFakeLock :
public CLockBase<LOCK_FAKELOCK, LOCK_MUTEX,
LOCK_RECURSIVE, LOCK_WAIT_SLEEP, LOCK_QUEUE_FIFO,
LOCK_NO_SPIN
>
{
private:
LOCK_INSTRUMENTATION_DECL();
public:
CFakeLock() {}
#ifdef LOCK_INSTRUMENTATION
CFakeLock(const char*) {}
#endif // LOCK_INSTRUMENTATION
~CFakeLock() {}
void WriteLock() {}
void ReadLock() {}
bool ReadOrWriteLock() {return true;}
bool TryWriteLock() {return true;}
bool TryReadLock() {return true;}
void WriteUnlock() {}
void ReadUnlock() {}
void ReadOrWriteUnlock(bool) {}
bool IsWriteLocked() const {return true;}
bool IsReadLocked() const {return IsWriteLocked();}
bool IsWriteUnlocked() const {return true;}
bool IsReadUnlocked() const {return true;}
void ConvertSharedToExclusive() {}
void ConvertExclusiveToShared() {}
bool SetSpinCount(WORD dwSpins) {return false;}
WORD GetSpinCount() const {return LOCK_DONT_SPIN;}
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CFakeLock";}
}; // CFakeLock
//--------------------------------------------------------------------
// A Win32 CRITICAL_SECTION
class IRTL_DLLEXP CCritSec :
public CLockBase<LOCK_CRITSEC, LOCK_MUTEX,
LOCK_RECURSIVE, LOCK_WAIT_HANDLE, LOCK_QUEUE_KERNEL,
LOCK_INDIVIDUAL_SPIN
>
{
private:
CRITICAL_SECTION m_cs;
LOCK_INSTRUMENTATION_DECL();
public:
CCritSec()
{
InitializeCriticalSection(&m_cs);
SetSpinCount(sm_wDefaultSpinCount);
}
#ifdef LOCK_INSTRUMENTATION
CCritSec(const char*)
{
InitializeCriticalSection(&m_cs);
SetSpinCount(sm_wDefaultSpinCount);
}
#endif // LOCK_INSTRUMENTATION
~CCritSec() { DeleteCriticalSection(&m_cs); }
void WriteLock() { EnterCriticalSection(&m_cs); }
void ReadLock() { WriteLock(); }
bool ReadOrWriteLock() { ReadLock(); return true; }
bool TryWriteLock();
bool TryReadLock() { return TryWriteLock(); }
void WriteUnlock() { LeaveCriticalSection(&m_cs); }
void ReadUnlock() { WriteUnlock(); }
void ReadOrWriteUnlock(bool) { ReadUnlock(); }
bool IsWriteLocked() const {return true;} // TODO: fix this
bool IsReadLocked() const {return IsWriteLocked();}
bool IsWriteUnlocked() const {return true;} // TODO: fix this
bool IsReadUnlocked() const {return true;} // TODO: fix this
// Convert a reader lock to a writer lock
void ConvertSharedToExclusive()
{
// no-op
}
// Convert a writer lock to a reader lock
void ConvertExclusiveToShared()
{
// no-op
}
// Wrapper for ::SetCriticalSectionSpinCount which was introduced
// in NT 4.0 sp3 and hence is not available on all platforms
static DWORD SetSpinCount(LPCRITICAL_SECTION pcs,
DWORD dwSpinCount=LOCK_DEFAULT_SPINS);
bool SetSpinCount(WORD wSpins)
{SetSpinCount(&m_cs, wSpins); return true;}
WORD GetSpinCount() const { return sm_wDefaultSpinCount; } // TODO
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CCritSec";}
}; // CCritSec
//--------------------------------------------------------------------
// CReaderWriterlock is a multi-reader, single-writer spinlock due to NJain,
// which in turn is derived from an exclusive spinlock by DmitryR.
// Gives priority to writers. Cannot be acquired recursively.
// No error checking. Use CReaderWriterLock3.
class IRTL_DLLEXP CReaderWriterLock :
public CLockBase<LOCK_READERWRITERLOCK, LOCK_MRSW,
LOCK_READ_RECURSIVE, LOCK_WAIT_SLEEP, LOCK_QUEUE_KERNEL,
LOCK_CLASS_SPIN
>
{
private:
volatile LONG m_nState; // > 0 => that many readers
volatile LONG m_cWaiting; // number of would-be writers
LOCK_INSTRUMENTATION_DECL();
private:
enum {
SL_FREE = 0,
SL_EXCLUSIVE = -1,
};
void _LockSpin(bool fWrite);
void _WriteLockSpin() { _LockSpin(true); }
void _ReadLockSpin() { _LockSpin(false); }
// _CmpExch is equivalent to
// LONG lTemp = m_lRW;
// if (lTemp == lCurrent) m_lRW = lNew;
// return lCurrent == lTemp;
// except it's one atomic instruction. Using this gives us the basis of
// a protocol because the update only succeeds when we knew exactly what
// used to be in m_lRW. If some other thread slips in and modifies m_lRW
// before we do, the update will fail. In other words, it's transactional.
LOCK_FORCEINLINE bool _CmpExch(LONG lNew, LONG lCurrent)
{
return lCurrent == Lock_AtomicCompareExchange(
const_cast<LONG*>(&m_nState), lNew, lCurrent);
}
LOCK_FORCEINLINE bool _TryWriteLock()
{
return (m_nState == SL_FREE && _CmpExch(SL_EXCLUSIVE, SL_FREE));
}
LOCK_FORCEINLINE bool _TryReadLock()
{
LONG nCurrState = m_nState;
// Give writers priority
return (nCurrState != SL_EXCLUSIVE && m_cWaiting == 0
&& _CmpExch(nCurrState + 1, nCurrState));
}
public:
CReaderWriterLock()
: m_nState(SL_FREE),
m_cWaiting(0)
{
}
#ifdef LOCK_INSTRUMENTATION
CReaderWriterLock(
const char* pszName)
: m_nState(SL_FREE),
m_cWaiting(0)
{
LOCK_INSTRUMENTATION_INIT(pszName);
}
#endif // LOCK_INSTRUMENTATION
#ifdef _DEBUG
~CReaderWriterLock()
{
IRTLASSERT(m_nState == SL_FREE && m_cWaiting == 0);
}
#endif // _DEBUG
inline void WriteLock()
{
LOCK_WRITELOCK_INSTRUMENTATION();
// Add ourselves to the queue of waiting writers
Lock_AtomicIncrement(const_cast<LONG*>(&m_cWaiting));
if (_TryWriteLock())
return;
_WriteLockSpin();
}
inline void ReadLock()
{
LOCK_READLOCK_INSTRUMENTATION();
if (_TryReadLock())
return;
_ReadLockSpin();
}
inline bool TryWriteLock()
{
// Add ourselves to the queue of waiting writers
Lock_AtomicIncrement(const_cast<LONG*>(&m_cWaiting));
if (_TryWriteLock())
{
LOCK_WRITELOCK_INSTRUMENTATION();
return true;
}
Lock_AtomicDecrement(const_cast<LONG*>(&m_cWaiting));
return false;
}
inline bool TryReadLock()
{
if (_TryReadLock())
{
LOCK_READLOCK_INSTRUMENTATION();
return true;
}
return false;
}
inline void WriteUnlock()
{
Lock_AtomicExchange(const_cast<LONG*>(&m_nState), SL_FREE);
Lock_AtomicDecrement(const_cast<LONG*>(&m_cWaiting));
}
inline void ReadUnlock()
{
Lock_AtomicDecrement(const_cast<LONG*>(&m_nState));
}
bool IsWriteLocked() const {return m_nState == SL_EXCLUSIVE;}
bool IsReadLocked() const {return m_nState > SL_FREE;}
bool IsWriteUnlocked() const {return m_nState != SL_EXCLUSIVE;}
bool IsReadUnlocked() const {return m_nState <= SL_FREE;}
void ConvertSharedToExclusive()
{
IRTLASSERT(IsReadLocked());
Lock_AtomicIncrement(const_cast<LONG*>(&m_cWaiting));
// single reader?
if (m_nState == SL_FREE + 1 && _CmpExch(SL_EXCLUSIVE, SL_FREE + 1))
return;
// release the reader lock and spin
Lock_AtomicDecrement(const_cast<LONG*>(&m_nState));
_WriteLockSpin();
IRTLASSERT(IsWriteLocked());
}
void ConvertExclusiveToShared()
{
IRTLASSERT(IsWriteLocked());
Lock_AtomicExchange(const_cast<LONG*>(&m_nState), SL_FREE + 1);
Lock_AtomicDecrement(const_cast<LONG*>(&m_cWaiting));
IRTLASSERT(IsReadLocked());
}
bool SetSpinCount(WORD wSpins) {return false;}
WORD GetSpinCount() const {return sm_wDefaultSpinCount;}
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CReaderWriterLock";}
}; // CReaderWriterLock
//--------------------------------------------------------------------
// CReaderWriterlock2 is a multi-reader, single-writer spinlock due to NJain,
// which in turn is derived from an exclusive spinlock by DmitryR.
// Gives priority to writers. Cannot be acquired recursively.
// No error checking. The difference between this and CReaderWriterLock is
// that all the state is packed into a single LONG, instead of two LONGs.
class IRTL_DLLEXP CReaderWriterLock2 :
public CLockBase<LOCK_READERWRITERLOCK2, LOCK_MRSW,
LOCK_READ_RECURSIVE, LOCK_WAIT_SLEEP, LOCK_QUEUE_KERNEL,
LOCK_CLASS_SPIN
>
{
private:
volatile LONG m_lRW;
// LoWord is state. ==0 => free; >0 => readers; ==0xFFFF => 1 writer.
// HiWord is count of writers, W.
// If LoWord==0xFFFF => W-1 waiters, 1 writer;
// otherwise W waiters.
enum {
SL_FREE = 0x00000000,
SL_STATE_MASK = 0x0000FFFF,
SL_STATE_SHIFT = 0,
SL_WAITING_MASK = 0xFFFF0000, // waiting writers
SL_WAITING_SHIFT = 16,
SL_READER_INCR = 0x00000001,
SL_READER_MASK = 0x00007FFF,
SL_EXCLUSIVE = 0x0000FFFF, // one writer
SL_WRITER_INCR = 0x00010000,
SL_ONE_WRITER = SL_EXCLUSIVE | SL_WRITER_INCR,
SL_ONE_READER = (SL_FREE + 1),
SL_WRITERS_MASK = ~SL_READER_MASK,
};
LOCK_INSTRUMENTATION_DECL();
private:
void _LockSpin(bool fWrite);
void _WriteLockSpin();
void _ReadLockSpin() { _LockSpin(false); }
// _CmpExch is equivalent to
// LONG lTemp = m_lRW;
// if (lTemp == lCurrent) m_lRW = lNew;
// return lCurrent == lTemp;
// except it's one atomic instruction. Using this gives us the basis of
// a protocol because the update only succeeds when we knew exactly what
// used to be in m_lRW. If some other thread slips in and modifies m_lRW
// before we do, the update will fail. In other words, it's transactional.
LOCK_FORCEINLINE bool _CmpExch(LONG lNew, LONG lCurrent)
{
return lCurrent ==Lock_AtomicCompareExchange(const_cast<LONG*>(&m_lRW),
lNew, lCurrent);
}
LOCK_FORCEINLINE bool _TryWriteLock(
LONG nIncr)
{
LONG l = m_lRW;
// Grab exclusive access to the lock if it's free. Works even
// if there are other writers queued up.
return ((l & SL_STATE_MASK) == SL_FREE
&& _CmpExch((l + nIncr) | SL_EXCLUSIVE, l));
}
LOCK_FORCEINLINE bool _TryReadLock()
{
LONG l = m_lRW;
// Give writers priority
return ((l & SL_WRITERS_MASK) == 0
&& _CmpExch(l + SL_READER_INCR, l));
}
public:
CReaderWriterLock2()
: m_lRW(SL_FREE)
{}
#ifdef LOCK_INSTRUMENTATION
CReaderWriterLock2(
const char* pszName)
: m_lRW(SL_FREE)
{
LOCK_INSTRUMENTATION_INIT(pszName);
}
#endif // LOCK_INSTRUMENTATION
#ifdef _DEBUG
~CReaderWriterLock2()
{
IRTLASSERT(m_lRW == SL_FREE);
}
#endif // _DEBUG
inline void WriteLock()
{
LOCK_WRITELOCK_INSTRUMENTATION();
// Optimize for the common case
if (_TryWriteLock(SL_WRITER_INCR))
return;
_WriteLockSpin();
}
inline void ReadLock()
{
LOCK_READLOCK_INSTRUMENTATION();
// Optimize for the common case
if (_TryReadLock())
return;
_ReadLockSpin();
}
inline bool TryWriteLock()
{
if (_TryWriteLock(SL_WRITER_INCR))
{
LOCK_WRITELOCK_INSTRUMENTATION();
return true;
}
return false;
}
inline bool TryReadLock()
{
if (_TryReadLock())
{
LOCK_READLOCK_INSTRUMENTATION();
return true;
}
return false;
}
inline void WriteUnlock()
{
IRTLASSERT(IsWriteLocked());
for (LONG l = m_lRW;
// decrement waiter count, clear loword to SL_FREE
!_CmpExch((l - SL_WRITER_INCR) & ~SL_STATE_MASK, l);
l = m_lRW)
{
IRTLASSERT(IsWriteLocked());
Lock_Yield();
}
}
inline void ReadUnlock()
{
IRTLASSERT(IsReadLocked());
for (LONG l = m_lRW; !_CmpExch(l - SL_READER_INCR, l); l = m_lRW)
{
IRTLASSERT(IsReadLocked());
Lock_Yield();
}
}
bool IsWriteLocked() const
{return (m_lRW & SL_STATE_MASK) == SL_EXCLUSIVE;}
bool IsReadLocked() const
{return (m_lRW & SL_READER_MASK) >= SL_READER_INCR ;}
bool IsWriteUnlocked() const
{return !IsWriteLocked();}
bool IsReadUnlocked() const
{return !IsReadLocked();}
void ConvertSharedToExclusive()
{
IRTLASSERT(IsReadLocked());
// single reader?
if (m_lRW != SL_ONE_READER || !_CmpExch(SL_ONE_WRITER,SL_ONE_READER))
{
// no, multiple readers
ReadUnlock();
_WriteLockSpin();
}
IRTLASSERT(IsWriteLocked());
}
void ConvertExclusiveToShared()
{
IRTLASSERT(IsWriteLocked());
for (LONG l = m_lRW;
!_CmpExch(((l-SL_WRITER_INCR) & SL_WAITING_MASK) | SL_READER_INCR,
l);
l = m_lRW)
{
IRTLASSERT(IsWriteLocked());
Lock_Yield();
}
IRTLASSERT(IsReadLocked());
}
bool SetSpinCount(WORD wSpins) {return false;}
WORD GetSpinCount() const {return sm_wDefaultSpinCount;}
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CReaderWriterLock2";}
}; // CReaderWriterLock2
//--------------------------------------------------------------------
// CReaderWriterLock3 is a multi-reader, single-writer spinlock due
// to NJain, which in turn is derived from an exclusive spinlock by DmitryR.
// Gives priority to writers. Cannot be acquired recursively.
// No error checking. Much like CReaderWriterLock2, except that the WriteLock
// can be acquired recursively.
class IRTL_DLLEXP CReaderWriterLock3 :
public CLockBase<LOCK_READERWRITERLOCK3, LOCK_MRSW,
LOCK_RECURSIVE, LOCK_WAIT_SLEEP, LOCK_QUEUE_KERNEL,
LOCK_CLASS_SPIN
>
{
private:
volatile LONG m_lRW; // Reader-Writer state
volatile LONG m_lTid; // Owning Thread ID + recursion count
// m_lRW:
// LoWord is state. =0 => free; >0 => readers; ==0xFFFF => 1 writer
// HiWord is count of writers. If LoWord==0xFFFF => N-1 waiters, 1 writer;
// otherwise N waiters.
// m_lTid:
// If readers, then 0; if a write lock, then thread id + recursion count
enum {
// m_lRW
SL_FREE = 0x00000000,
SL_STATE_MASK = 0x0000FFFF,
SL_STATE_SHIFT = 0,
SL_WAITING_MASK = 0xFFFF0000, // waiting writers
SL_WAITING_SHIFT = 16,
SL_READER_INCR = 0x00000001,
SL_READER_MASK = 0x00007FFF,
SL_EXCLUSIVE = 0x0000FFFF, // one writer
SL_WRITER_INCR = 0x00010000,
SL_ONE_WRITER = SL_EXCLUSIVE | SL_WRITER_INCR,
SL_ONE_READER = (SL_FREE + 1),
SL_WRITERS_MASK = ~SL_READER_MASK,
// m_lTid
SL_THREAD_SHIFT = 0,
SL_THREAD_BITS = 28,
SL_OWNER_SHIFT = SL_THREAD_BITS,
SL_OWNER_BITS = 4,
SL_THREAD_MASK = ((1 << SL_THREAD_BITS) - 1) << SL_THREAD_SHIFT,
SL_OWNER_INCR = 1 << SL_THREAD_BITS,
SL_OWNER_MASK = ((1 << SL_OWNER_BITS) - 1) << SL_OWNER_SHIFT,
};
LOCK_INSTRUMENTATION_DECL();
private:
void _LockSpin(bool fWrite);
void _WriteLockSpin();
void _ReadLockSpin() { _LockSpin(false); }
// _CmpExch is equivalent to
// LONG lTemp = m_lRW;
// if (lTemp == lCurrent) m_lRW = lNew;
// return lCurrent == lTemp;
// except it's one atomic instruction. Using this gives us the basis of
// a protocol because the update only succeeds when we knew exactly what
// used to be in m_lRW. If some other thread slips in and modifies m_lRW
// before we do, the update will fail. In other words, it's transactional.
LOCK_FORCEINLINE bool _CmpExch(LONG lNew, LONG lCurrent)
{
return lCurrent==Lock_AtomicCompareExchange(const_cast<LONG*>(&m_lRW),
lNew, lCurrent);
}
// Get the current thread ID. Assumes that it can fit into 28 bits,
// which is fairly safe as NT recycles thread IDs and failing to fit into
// 28 bits would mean that more than 268,435,456 threads were currently
// active. This is improbable in the extreme as NT runs out of
// resources if there are more than a few thousands threads in
// existence and the overhead of context swapping becomes unbearable.
inline static LONG _CurrentThreadId()
{
DWORD dwTid = ::GetCurrentThreadId();
// Thread ID 0 is used by the System Process (Process ID 0).
// We use a thread-id of zero to indicate lock is unowned.
// NT uses +ve thread ids, Win9x uses -ve ids
IRTLASSERT(dwTid != 0
&& ((dwTid <= SL_THREAD_MASK) || (dwTid > ~SL_THREAD_MASK)));
return (LONG) (dwTid & SL_THREAD_MASK);
}
LOCK_FORCEINLINE bool _TryWriteLock(
LONG nIncr)
{
// The common case: the writelock has no owner
if (m_lTid == 0)
{
// IRTLASSERT((m_lRW & SL_STATE_MASK) != SL_EXCLUSIVE);
LONG l = m_lRW;
// Grab exclusive access to the lock if it's free. Works even
// if there are other writers queued up.
if ((l & SL_STATE_MASK) == SL_FREE
&& _CmpExch((l + nIncr) | SL_EXCLUSIVE, l))
{
l = Lock_AtomicExchange(const_cast<LONG*>(&m_lTid),
_CurrentThreadId() | SL_OWNER_INCR);
IRTLASSERT(l == 0);
return true;
}
}
return _TryWriteLock2();
}
// split into a separate function to make _TryWriteLock more inlineable
bool _TryWriteLock2()
{
if ((m_lTid & SL_THREAD_MASK) == _CurrentThreadId())
{
IRTLASSERT((m_lRW & SL_STATE_MASK) == SL_EXCLUSIVE);
IRTLASSERT((m_lTid & SL_OWNER_MASK) != SL_OWNER_MASK);
Lock_AtomicExchangeAdd(const_cast<LONG*>(&m_lTid), SL_OWNER_INCR);
return true;
}
return false;
}
LOCK_FORCEINLINE bool _TryReadLock()
{
LONG l = m_lRW;
// Give writers priority
bool f = ((l & SL_WRITERS_MASK) == 0
&& _CmpExch(l + SL_READER_INCR, l));
IRTLASSERT(!f || m_lTid == 0);
return f;
}
public:
CReaderWriterLock3()
: m_lRW(SL_FREE),
m_lTid(0)
{}
#ifdef LOCK_INSTRUMENTATION
CReaderWriterLock3(
const char* pszName)
: m_lRW(SL_FREE),
m_lTid(0)
{
LOCK_INSTRUMENTATION_INIT(pszName);
}
#endif // LOCK_INSTRUMENTATION
#ifdef _DEBUG
~CReaderWriterLock3()
{
IRTLASSERT(m_lRW == SL_FREE && m_lTid == 0);
}
#endif // _DEBUG
inline void WriteLock()
{
LOCK_WRITELOCK_INSTRUMENTATION();
// Optimize for the common case
if (_TryWriteLock(SL_WRITER_INCR))
return;
_WriteLockSpin();
}
inline void ReadLock()
{
LOCK_READLOCK_INSTRUMENTATION();
// Optimize for the common case
if (_TryReadLock())
return;
_ReadLockSpin();
}
// If already locked, recursively acquires another lock of the same
// kind (read or write). Otherwise, just acquires a read lock.
// Needed for cases like this.
// pTable->WriteLock();
// if (!pTable->FindKey(&SomeKey))
// InsertRecord(&Whatever);
// pTable->WriteUnlock();
// where FindKey looks like
// Table::FindKey(pKey) {
// ReadOrWriteLock();
// // find pKey if present in table
// ReadOrWriteUnlock();
// }
// and InsertRecord looks like
// Table::InsertRecord(pRecord) {
// WriteLock();
// // insert pRecord into table
// WriteUnlock();
// }
// If FindKey called ReadLock while the thread already had done a
// WriteLock, the thread would deadlock.
inline bool ReadOrWriteLock()
{
if (IsWriteLocked())
{
WriteLock();
return false;
}
else
{
ReadLock();
return true;
}
}
inline bool TryWriteLock()
{
if (_TryWriteLock(SL_WRITER_INCR))
{
LOCK_WRITELOCK_INSTRUMENTATION();
return true;
}
return false;
}
inline bool TryReadLock()
{
if (_TryReadLock())
{
LOCK_READLOCK_INSTRUMENTATION();
return true;
}
return false;
}
inline void WriteUnlock()
{
IRTLASSERT(IsWriteLocked());
LONG lNew = m_lTid - SL_OWNER_INCR;
// Last owner? Release completely, if so
if ((lNew & SL_OWNER_MASK) == 0)
{
Lock_AtomicExchange(const_cast<LONG*>(&m_lTid), 0);
for (LONG l = m_lRW;
// decrement waiter count, clear loword to SL_FREE
!_CmpExch((l - SL_WRITER_INCR) & ~SL_STATE_MASK, l);
l = m_lRW)
{
Lock_Yield();
}
}
else
Lock_AtomicExchange(const_cast<LONG*>(&m_lTid), lNew);
}
inline void ReadUnlock()
{
IRTLASSERT(IsReadLocked());
for (LONG l = m_lRW; !_CmpExch(l - SL_READER_INCR, l); l = m_lRW)
{
IRTLASSERT(IsReadLocked());
Lock_Yield();
}
}
inline void ReadOrWriteUnlock(bool fIsReadLocked)
{
if (fIsReadLocked)
ReadUnlock();
else
WriteUnlock();
}
// Does current thread hold a write lock?
bool IsWriteLocked() const
{
// bool fLocked = ((m_lTid & SL_THREAD_MASK) == _CurrentThreadId());
bool fLocked = !((m_lTid ^ GetCurrentThreadId()) & SL_THREAD_MASK);
IRTLASSERT(!fLocked || (((m_lRW & SL_STATE_MASK) == SL_EXCLUSIVE)
&& ((m_lTid & SL_OWNER_MASK) > 0)));
return fLocked;
}
bool IsReadLocked() const
{return (m_lRW & SL_READER_MASK) >= SL_READER_INCR ;}
bool IsWriteUnlocked() const
{return !IsWriteLocked();}
bool IsReadUnlocked() const
{return !IsReadLocked();}
// Note: if there's more than one reader, then there's a window where
// another thread can acquire and release a writelock before this routine
// returns.
void ConvertSharedToExclusive()
{
IRTLASSERT(IsReadLocked());
// single reader?
if (m_lRW == SL_ONE_READER && _CmpExch(SL_ONE_WRITER, SL_ONE_READER))
{
Lock_AtomicExchange(const_cast<LONG*>(&m_lTid),
_CurrentThreadId() | SL_OWNER_INCR);
}
else
{
// no, multiple readers
ReadUnlock();
_WriteLockSpin();
}
IRTLASSERT(IsWriteLocked());
}
// There is no such window when converting from a writelock to a readlock
void ConvertExclusiveToShared()
{
IRTLASSERT(IsWriteLocked());
// assume writelock is not held recursively
IRTLASSERT((m_lTid & SL_OWNER_MASK) == SL_OWNER_INCR);
Lock_AtomicExchange(const_cast<LONG*>(&m_lTid), 0);
for (LONG l = m_lRW;
!_CmpExch(((l-SL_WRITER_INCR) & SL_WAITING_MASK) | SL_READER_INCR,
l);
l = m_lRW)
{
Lock_Yield();
}
IRTLASSERT(IsReadLocked());
}
bool SetSpinCount(WORD wSpins) {return false;}
WORD GetSpinCount() const {return sm_wDefaultSpinCount;}
LOCK_DEFAULT_SPIN_IMPLEMENTATION();
static const char* ClassName() {return "CReaderWriterLock3";}
}; // CReaderWriterLock3
#ifdef __LOCKS_NAMESPACE__
}
#endif // __LOCKS_NAMESPACE__
#endif // __LOCKS_H__
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