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windows-nt/Source/XPSP1/NT/inetsrv/iis/svcs/iisrtl/locks.cpp

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/*++
Copyright (c) 1998-1999 Microsoft Corporation
Module Name :
locks.cpp
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:
--*/
#include "precomp.hxx"
#define DLL_IMPLEMENTATION
#define IMPLEMENTATION_EXPORT
#include <locks.h>
#ifdef __LOCKS_NAMESPACE__
namespace Locks {
#endif // __LOCKS_NAMESPACE__
#define LOCK_DEFAULT_SPIN_DATA(CLASS) \
WORD CLASS::sm_wDefaultSpinCount = LOCK_DEFAULT_SPINS; \
double CLASS::sm_dblDfltSpinAdjFctr = 0.5
#ifdef LOCK_INSTRUMENTATION
# define LOCK_STATISTICS_DATA(CLASS) \
LONG CLASS::sm_cTotalLocks = 0; \
LONG CLASS::sm_cContendedLocks = 0; \
LONG CLASS::sm_nSleeps = 0; \
LONGLONG CLASS::sm_cTotalSpins = 0; \
LONG CLASS::sm_nReadLocks = 0; \
LONG CLASS::sm_nWriteLocks = 0
# define LOCK_STATISTICS_DUMMY_IMPLEMENTATION(CLASS) \
CLockStatistics CLASS::Statistics() const \
{return CLockStatistics();} \
CGlobalLockStatistics CLASS::GlobalStatistics() \
{return CGlobalLockStatistics();} \
void CLASS::ResetGlobalStatistics() \
{}
# define LOCK_STATISTICS_REAL_IMPLEMENTATION(CLASS) \
\
/* Per-lock statistics */ \
CLockStatistics \
CLASS::Statistics() const \
{ \
CLockStatistics ls; \
\
ls.m_nContentions = m_nContentions; \
ls.m_nSleeps = m_nSleeps; \
ls.m_nContentionSpins = m_nContentionSpins; \
if (m_nContentions > 0) \
ls.m_nAverageSpins = m_nContentionSpins / m_nContentions;\
else \
ls.m_nAverageSpins = 0; \
ls.m_nReadLocks = m_nReadLocks; \
ls.m_nWriteLocks = m_nWriteLocks; \
strcpy(ls.m_szName, m_szName); \
\
return ls; \
} \
\
\
/* Global statistics for CLASS */ \
CGlobalLockStatistics \
CLASS::GlobalStatistics() \
{ \
CGlobalLockStatistics gls; \
\
gls.m_cTotalLocks = sm_cTotalLocks; \
gls.m_cContendedLocks = sm_cContendedLocks; \
gls.m_nSleeps = sm_nSleeps; \
gls.m_cTotalSpins = sm_cTotalSpins; \
if (sm_cContendedLocks > 0) \
gls.m_nAverageSpins = static_cast<LONG>(sm_cTotalSpins / \
sm_cContendedLocks);\
else \
gls.m_nAverageSpins = 0; \
gls.m_nReadLocks = sm_nReadLocks; \
gls.m_nWriteLocks = sm_nWriteLocks; \
\
return gls; \
} \
\
\
/* Reset global statistics for CLASS */ \
void \
CLASS::ResetGlobalStatistics() \
{ \
sm_cTotalLocks = 0; \
sm_cContendedLocks = 0; \
sm_nSleeps = 0; \
sm_cTotalSpins = 0; \
sm_nReadLocks = 0; \
sm_nWriteLocks = 0; \
}
// 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_INSTRUMENTATION_PROLOG() \
++sm_cContendedLocks; \
LONG cTotalSpins = 0; \
WORD cSleeps = 0
// Don't need InterlockedIncrement or InterlockedExchangeAdd for
// member variables, as the lock is now locked by this thread.
# define LOCK_INSTRUMENTATION_EPILOG() \
++m_nContentions; \
m_nSleeps += cSleeps; \
m_nContentionSpins += cTotalSpins; \
sm_nSleeps += cSleeps; \
sm_cTotalSpins += cTotalSpins
#else // !LOCK_INSTRUMENTATION
# define LOCK_STATISTICS_DATA(CLASS)
# define LOCK_STATISTICS_DUMMY_IMPLEMENTATION(CLASS)
# define LOCK_STATISTICS_REAL_IMPLEMENTATION(CLASS)
# define LOCK_INSTRUMENTATION_PROLOG()
# define LOCK_INSTRUMENTATION_EPILOG()
#endif // !LOCK_INSTRUMENTATION
//------------------------------------------------------------------------
// Function: RandomBackoffFactor
// Synopsis: A fudge factor to help avoid synchronization problems
//------------------------------------------------------------------------
double
RandomBackoffFactor()
{
static const double s_aFactors[] = {
1.020, 0.965, 0.890, 1.065,
1.025, 1.115, 0.940, 0.995,
1.050, 1.080, 0.915, 0.980,
1.010,
};
const int nFactors = sizeof(s_aFactors) / sizeof(s_aFactors[0]);
// Alternatives for nRand include a static counter
// or the low DWORD of QueryPerformanceCounter().
DWORD nRand = ::GetCurrentThreadId();
return s_aFactors[nRand % nFactors];
}
// CSmallSpinLock static member variables
LOCK_DEFAULT_SPIN_DATA(CSmallSpinLock);
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_STATISTICS_DATA(CSmallSpinLock);
LOCK_STATISTICS_REAL_IMPLEMENTATION(CSmallSpinLock);
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
//------------------------------------------------------------------------
// Function: CSmallSpinLock::_LockSpin
// Synopsis: Acquire an exclusive lock. Blocks until acquired.
//------------------------------------------------------------------------
void
CSmallSpinLock::_LockSpin()
{
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_INSTRUMENTATION_PROLOG();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
DWORD dwSleepTime = 0;
LONG cBaseSpins = sm_wDefaultSpinCount;
LONG cBaseSpins2 = static_cast<LONG>(cBaseSpins * RandomBackoffFactor());
// This lock cannot be acquired recursively. Attempting to do so will
// deadlock this thread forever. Use CSpinLock instead if you need that
// kind of lock.
if (m_lTid == (LONG) ::GetCurrentThreadId())
{
IRTLASSERT(
!"CSmallSpinLock: Illegally attempted to acquire lock recursively");
}
while (!_TryLock())
{
// Only spin on a multiprocessor machine and then only if
// spinning is enabled
if (NumProcessors() > 1 && cBaseSpins != LOCK_DONT_SPIN)
{
LONG cSpins = cBaseSpins2;
// Check no more than cBaseSpins2 times then yield.
// It is important not to use the InterlockedExchange in the
// inner loop in order to minimize system memory bus traffic.
while (m_lTid != 0)
{
if (--cSpins < 0)
{
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
cTotalSpins += cBaseSpins2;
++cSleeps;
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
Sleep(dwSleepTime) ;
// Backoff algorithm: reduce (or increase) busy wait time
cBaseSpins2 = (int) (cBaseSpins2 * sm_dblDfltSpinAdjFctr);
// LOCK_MINIMUM_SPINS <= cBaseSpins2 <= LOCK_MAXIMUM_SPINS
cBaseSpins2 = min(LOCK_MAXIMUM_SPINS, cBaseSpins2);
cBaseSpins2 = max(cBaseSpins2, LOCK_MINIMUM_SPINS);
cSpins = cBaseSpins2;
// Using Sleep(0) leads to the possibility of priority
// inversion. Sleep(0) only yields the processor if
// there's another thread of the same priority that's
// ready to run. If a high-priority thread is trying to
// acquire the lock, which is held by a low-priority
// thread, then the low-priority thread may never get
// scheduled and hence never free the lock. NT attempts
// to avoid priority inversions by temporarily boosting
// the priority of low-priority runnable threads, but the
// problem can still occur if there's a medium-priority
// thread that's always runnable. If Sleep(1) is used,
// then the thread unconditionally yields the CPU. We
// only do this for the second and subsequent even
// iterations, since a millisecond is a long time to wait
// if the thread can be scheduled in again sooner
// (~100,000 instructions).
// Avoid priority inversion: 0, 1, 0, 1,...
dwSleepTime = !dwSleepTime;
}
else
{
Lock_Yield();
}
}
// Lock is now available, but we still need to do the
// InterlockedExchange to atomically grab it for ourselves.
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
cTotalSpins += cBaseSpins2 - cSpins;
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
}
// On a 1P machine, busy waiting is a waste of time
else
{
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
++cSleeps;
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
Sleep(dwSleepTime);
// Avoid priority inversion: 0, 1, 0, 1,...
dwSleepTime = !dwSleepTime;
}
}
#ifdef LOCK_SMALL_SPIN_INSTRUMENTATION
LOCK_INSTRUMENTATION_EPILOG();
#endif // LOCK_SMALL_SPIN_INSTRUMENTATION
}
// CSpinLock static member variables
LOCK_DEFAULT_SPIN_DATA(CSpinLock);
LOCK_STATISTICS_DATA(CSpinLock);
LOCK_STATISTICS_REAL_IMPLEMENTATION(CSpinLock);
//------------------------------------------------------------------------
// Function: CSpinLock::_LockSpin
// Synopsis: Acquire an exclusive lock. Blocks until acquired.
//------------------------------------------------------------------------
void
CSpinLock::_LockSpin()
{
LOCK_INSTRUMENTATION_PROLOG();
DWORD dwSleepTime = 0;
bool fAcquiredLock = false;
LONG cBaseSpins = sm_wDefaultSpinCount;
cBaseSpins = static_cast<LONG>(cBaseSpins * RandomBackoffFactor());
while (!fAcquiredLock)
{
// Only spin on a multiprocessor machine and then only if
// spinning is enabled
if (NumProcessors() > 1 && sm_wDefaultSpinCount != LOCK_DONT_SPIN)
{
LONG cSpins = cBaseSpins;
// Check no more than cBaseSpins times then yield
while (m_lTid != 0)
{
if (--cSpins < 0)
{
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += cBaseSpins;
++cSleeps;
#endif // LOCK_INSTRUMENTATION
Sleep(dwSleepTime) ;
// Backoff algorithm: reduce (or increase) busy wait time
cBaseSpins = (int) (cBaseSpins * sm_dblDfltSpinAdjFctr);
// LOCK_MINIMUM_SPINS <= cBaseSpins <= LOCK_MAXIMUM_SPINS
cBaseSpins = min(LOCK_MAXIMUM_SPINS, cBaseSpins);
cBaseSpins = max(cBaseSpins, LOCK_MINIMUM_SPINS);
cSpins = cBaseSpins;
// Avoid priority inversion: 0, 1, 0, 1,...
dwSleepTime = !dwSleepTime;
}
else
{
Lock_Yield();
}
}
// Lock is now available, but we still need to atomically
// update m_cOwners and m_nThreadId to grab it for ourselves.
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += cBaseSpins - cSpins;
#endif // LOCK_INSTRUMENTATION
}
// on a 1P machine, busy waiting is a waste of time
else
{
#ifdef LOCK_INSTRUMENTATION
++cSleeps;
#endif // LOCK_INSTRUMENTATION
Sleep(dwSleepTime);
// Avoid priority inversion: 0, 1, 0, 1,...
dwSleepTime = !dwSleepTime;
}
// Is the lock unowned?
if (_TryLock())
fAcquiredLock = true; // got the lock
}
IRTLASSERT((m_lTid & OWNER_MASK) > 0
&& (m_lTid & THREAD_MASK) == _CurrentThreadId());
LOCK_INSTRUMENTATION_EPILOG();
}
// CFakeLock static member variables
LOCK_DEFAULT_SPIN_DATA(CFakeLock);
LOCK_STATISTICS_DATA(CFakeLock);
LOCK_STATISTICS_DUMMY_IMPLEMENTATION(CFakeLock);
// CCritSec static member variables
LOCK_DEFAULT_SPIN_DATA(CCritSec);
LOCK_STATISTICS_DATA(CCritSec);
LOCK_STATISTICS_DUMMY_IMPLEMENTATION(CCritSec);
//------------------------------------------------------------------------
// SetCriticalSectionSpinCount hackery
typedef
DWORD
(WINAPI * PFN_SET_CRITICAL_SECTION_SPIN_COUNT)(
LPCRITICAL_SECTION lpCriticalSection,
DWORD dwSpinCount
);
static PFN_SET_CRITICAL_SECTION_SPIN_COUNT g_pfnSetCSSpinCount = NULL;
//------------------------------------------------------------------------
// Function: FakeSetCriticalSectionSpinCount
// Synopsis: This function fakes setting critical section spin count.
// See CCritSec::SetSpinCount() for details
// Returns: 0 - since we are faking the set of cs with spin count
//------------------------------------------------------------------------
static DWORD WINAPI
FakeSetCriticalSectionSpinCount(
LPCRITICAL_SECTION /*lpCriticalSection*/,
DWORD /*dwSpinCount*/)
{
// For faked critical sections, the previous spin count is just ZERO!
return 0;
}
//------------------------------------------------------------------------
// Function: CCritSec::SetSpinCount
// Synopsis: This function is used to call the appropriate underlying
// functions to set the spin count for the supplied critical
// section. The original function is supposed to be exported out
// of kernel32.dll from NT 4.0 SP3. If the func is not available
// from the dll, we will use a fake function.
//
// Arguments:
// lpCriticalSection
// Points to the critical section object.
//
// dwSpinCount
// Supplies the spin count for the critical section object. For UP
// systems, the spin count is ignored and the critical section spin
// count is set to 0. For MP systems, if contention occurs, instead of
// waiting on a semaphore associated with the critical section, the
// calling thread will spin for spin count iterations before doing the
// hard wait. If the critical section becomes free during the spin, a
// wait is avoided.
//
// Returns:
// The previous spin count for the critical section is returned.
//------------------------------------------------------------------------
DWORD
CCritSec::SetSpinCount(
LPCRITICAL_SECTION pcs,
DWORD dwSpinCount)
{
if (g_pfnSetCSSpinCount == NULL)
{
PFN_SET_CRITICAL_SECTION_SPIN_COUNT pfn = NULL;
//
// load kernel32 and get NT specific entry points
//
HINSTANCE tmpInstance = LoadLibrary("kernel32.dll");
if (tmpInstance != NULL)
{
pfn = (PFN_SET_CRITICAL_SECTION_SPIN_COUNT)
GetProcAddress(tmpInstance, "SetCriticalSectionSpinCount");
//
// We can free this because we are statically linked to it
//
FreeLibrary(tmpInstance);
}
// fallback to thunking to the dummy routine
g_pfnSetCSSpinCount = ((pfn != NULL)
? pfn
: FakeSetCriticalSectionSpinCount);
}
// Pass the inputs to the global function pointer which is already setup.
return g_pfnSetCSSpinCount(pcs, dwSpinCount);
}
// CRtlResource static member variables
LOCK_DEFAULT_SPIN_DATA(CRtlResource);
LOCK_STATISTICS_DATA(CRtlResource);
LOCK_STATISTICS_DUMMY_IMPLEMENTATION(CRtlResource);
// CShareLock static member variables
LOCK_DEFAULT_SPIN_DATA(CShareLock);
LOCK_STATISTICS_DATA(CShareLock);
LOCK_STATISTICS_DUMMY_IMPLEMENTATION(CShareLock);
// CReaderWriterLock static member variables
LOCK_DEFAULT_SPIN_DATA(CReaderWriterLock);
LOCK_STATISTICS_DATA(CReaderWriterLock);
LOCK_STATISTICS_REAL_IMPLEMENTATION(CReaderWriterLock);
void
CReaderWriterLock::_LockSpin(
bool fWrite)
{
LOCK_INSTRUMENTATION_PROLOG();
DWORD dwSleepTime = 0;
LONG cBaseSpins = static_cast<LONG>(sm_wDefaultSpinCount
* RandomBackoffFactor());
LONG cSpins = cBaseSpins;
for (;;)
{
if (NumProcessors() < 2 || sm_wDefaultSpinCount == LOCK_DONT_SPIN)
cSpins = 1; // must loop once to call _TryRWLock
for (int i = cSpins; --i >= 0; )
{
bool fLock = fWrite ? _TryWriteLock() : _TryReadLock();
if (fLock)
{
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += (cSpins - i - 1);
#endif // LOCK_INSTRUMENTATION
goto locked;
}
Lock_Yield();
}
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += cBaseSpins;
++cSleeps;
#endif // LOCK_INSTRUMENTATION
Sleep(dwSleepTime) ;
dwSleepTime = !dwSleepTime; // Avoid priority inversion: 0, 1, 0, 1,...
// Backoff algorithm: reduce (or increase) busy wait time
cBaseSpins = (int) (cBaseSpins * sm_dblDfltSpinAdjFctr);
// LOCK_MINIMUM_SPINS <= cBaseSpins <= LOCK_MAXIMUM_SPINS
cBaseSpins = min(LOCK_MAXIMUM_SPINS, cBaseSpins);
cBaseSpins = max(cBaseSpins, LOCK_MINIMUM_SPINS);
cSpins = cBaseSpins;
}
locked:
IRTLASSERT(fWrite ? IsWriteLocked() : IsReadLocked());
LOCK_INSTRUMENTATION_EPILOG();
}
// CReaderWriterLock2 static member variables
LOCK_DEFAULT_SPIN_DATA(CReaderWriterLock2);
LOCK_STATISTICS_DATA(CReaderWriterLock2);
LOCK_STATISTICS_REAL_IMPLEMENTATION(CReaderWriterLock2);
void
CReaderWriterLock2::_WriteLockSpin()
{
// Add ourselves to the queue of waiting writers
for (LONG l = m_lRW; !_CmpExch(l + SL_WRITER_INCR, l); l = m_lRW)
{
Lock_Yield();
}
_LockSpin(true);
}
void
CReaderWriterLock2::_LockSpin(
bool fWrite)
{
LOCK_INSTRUMENTATION_PROLOG();
DWORD dwSleepTime = 0;
LONG cBaseSpins = static_cast<LONG>(sm_wDefaultSpinCount
* RandomBackoffFactor());
LONG cSpins = cBaseSpins;
for (;;)
{
if (NumProcessors() < 2 || sm_wDefaultSpinCount == LOCK_DONT_SPIN)
cSpins = 1; // must loop once to call _TryRWLock
for (int i = cSpins; --i >= 0; )
{
bool fLock = fWrite ? _TryWriteLock(0) : _TryReadLock();
if (fLock)
{
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += (cSpins - i - 1);
#endif // LOCK_INSTRUMENTATION
goto locked;
}
Lock_Yield();
}
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += cBaseSpins;
++cSleeps;
#endif // LOCK_INSTRUMENTATION
Sleep(dwSleepTime) ;
dwSleepTime = !dwSleepTime; // Avoid priority inversion: 0, 1, 0, 1,...
// Backoff algorithm: reduce (or increase) busy wait time
cBaseSpins = (int) (cBaseSpins * sm_dblDfltSpinAdjFctr);
// LOCK_MINIMUM_SPINS <= cBaseSpins <= LOCK_MAXIMUM_SPINS
cBaseSpins = min(LOCK_MAXIMUM_SPINS, cBaseSpins);
cBaseSpins = max(cBaseSpins, LOCK_MINIMUM_SPINS);
cSpins = cBaseSpins;
}
locked:
IRTLASSERT(fWrite ? IsWriteLocked() : IsReadLocked());
LOCK_INSTRUMENTATION_EPILOG();
}
// CReaderWriterLock3 static member variables
LOCK_DEFAULT_SPIN_DATA(CReaderWriterLock3);
LOCK_STATISTICS_DATA(CReaderWriterLock3);
LOCK_STATISTICS_REAL_IMPLEMENTATION(CReaderWriterLock3);
void
CReaderWriterLock3::_WriteLockSpin()
{
// Add ourselves to the queue of waiting writers
for (LONG l = m_lRW; !_CmpExch(l + SL_WRITER_INCR, l); l = m_lRW)
{
Lock_Yield();
}
_LockSpin(true);
}
void
CReaderWriterLock3::_LockSpin(
bool fWrite)
{
LOCK_INSTRUMENTATION_PROLOG();
DWORD dwSleepTime = 0;
LONG cBaseSpins = static_cast<LONG>(sm_wDefaultSpinCount
* RandomBackoffFactor());
LONG cSpins = cBaseSpins;
for (;;)
{
if (NumProcessors() < 2 || sm_wDefaultSpinCount == LOCK_DONT_SPIN)
cSpins = 1; // must loop once to call _TryRWLock
for (int i = cSpins; --i >= 0; )
{
bool fLock = fWrite ? _TryWriteLock(0) : _TryReadLock();
if (fLock)
{
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += (cSpins - i - 1);
#endif // LOCK_INSTRUMENTATION
goto locked;
}
Lock_Yield();
}
#ifdef LOCK_INSTRUMENTATION
cTotalSpins += cBaseSpins;
++cSleeps;
#endif // LOCK_INSTRUMENTATION
Sleep(dwSleepTime) ;
dwSleepTime = !dwSleepTime; // Avoid priority inversion: 0, 1, 0, 1,...
// Backoff algorithm: reduce (or increase) busy wait time
cBaseSpins = (int) (cBaseSpins * sm_dblDfltSpinAdjFctr);
// LOCK_MINIMUM_SPINS <= cBaseSpins <= LOCK_MAXIMUM_SPINS
cBaseSpins = min(LOCK_MAXIMUM_SPINS, cBaseSpins);
cBaseSpins = max(cBaseSpins, LOCK_MINIMUM_SPINS);
cSpins = cBaseSpins;
}
locked:
IRTLASSERT(fWrite ? IsWriteLocked() : IsReadLocked());
LOCK_INSTRUMENTATION_EPILOG();
}
#ifdef __LOCKS_NAMESPACE__
}
#endif // __LOCKS_NAMESPACE__
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