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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
//
// spinlock.cpp
//
//
#include "common.h"
#include "slist.h"
#include "spinlock.h"
#include "threads.h"
#include "corhost.h"
enum
{
BACKOFF_LIMIT = 1000 // used in spin to acquire
};
#ifdef _DEBUG
// profile information
ULONG SpinLockProfiler::s_ulBackOffs = 0;
ULONG SpinLockProfiler::s_ulCollisons [LOCK_TYPE_DEFAULT + 1] = { 0 };
ULONG SpinLockProfiler::s_ulSpins [LOCK_TYPE_DEFAULT + 1] = { 0 };
#endif
SpinLock::SpinLock()
{
// Global SpinLock variables will cause the constructor to be
// called during DllInit, which means we cannot use full contracts
// because we have not called InitUtilCode yet.
STATIC_CONTRACT_NOTHROW;
STATIC_CONTRACT_GC_NOTRIGGER;
m_Initialized = UnInitialized;
}
SpinLock::~SpinLock()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
}
CONTRACTL_END;
}
void SpinLock::Init(LOCK_TYPE type, bool RequireCoopGC)
{
CONTRACTL
{
THROWS;
GC_NOTRIGGER;
}
CONTRACTL_END;
if (m_Initialized == Initialized)
{
_ASSERTE (type == m_LockType);
_ASSERTE (RequireCoopGC == m_requireCoopGCMode);
// We have initialized this spinlock.
return;
}
while (TRUE)
{
LONG curValue = FastInterlockCompareExchange((LONG*)&m_Initialized, BeingInitialized, UnInitialized);
if (curValue == Initialized)
{
return;
}
else if (curValue == UnInitialized)
{
// We are the first to initialize the lock
break;
}
else
{
__SwitchToThread(10, CALLER_LIMITS_SPINNING);
}
}
{
m_lock = 0;
}
#ifdef _DEBUG
m_LockType = type;
m_requireCoopGCMode = RequireCoopGC;
#endif
_ASSERTE (m_Initialized == BeingInitialized);
m_Initialized = Initialized;
}
#ifdef _DEBUG
BOOL SpinLock::OwnedByCurrentThread()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
return m_holdingThreadId.IsCurrentThread();
}
#endif
DEBUG_NOINLINE void SpinLock::AcquireLock(SpinLock *s, Thread * pThread)
{
SCAN_SCOPE_BEGIN;
STATIC_CONTRACT_GC_NOTRIGGER;
s->GetLock(pThread);
}
DEBUG_NOINLINE void SpinLock::ReleaseLock(SpinLock *s, Thread * pThread)
{
SCAN_SCOPE_END;
s->FreeLock(pThread);
}
void SpinLock::GetLock(Thread* pThread)
{
CONTRACTL
{
DISABLED(THROWS); // need to rewrite spin locks to no-throw.
GC_NOTRIGGER;
CAN_TAKE_LOCK;
SO_TOLERANT;
}
CONTRACTL_END;
_ASSERTE(m_Initialized == Initialized);
#ifdef _DEBUG
dbg_PreEnterLock();
#endif
{
// Not CLR Sync hosted, so we use interlocked operations on
// m_lock to acquire the lock. This will automatically cause
// us to call EE_LOCK_TAKEN(this);
if (!GetLockNoWait())
{
SpinToAcquire();
}
}
INCTHREADLOCKCOUNTTHREAD(pThread);
#ifdef _DEBUG
m_holdingThreadId.SetToCurrentThread();
dbg_EnterLock();
#endif
}
//----------------------------------------------------------------------------
// SpinLock::GetLockNoWait
// used interlocked exchange and fast lock acquire
BOOL SpinLock::GetLockNoWait()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
CAN_TAKE_LOCK;
SO_TOLERANT;
}
CONTRACTL_END;
{
if (VolatileLoad(&m_lock) == 0 && FastInterlockExchange (&m_lock, 1) == 0)
{
EE_LOCK_TAKEN(this);
return 1;
}
return 0;
}
}
//----------------------------------------------------------------------------
// SpinLock::FreeLock
// Release the spinlock
//
void SpinLock::FreeLock(Thread* pThread)
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
SO_TOLERANT;
}
CONTRACTL_END;
_ASSERTE(m_Initialized == Initialized);
#ifdef _DEBUG
_ASSERTE(OwnedByCurrentThread());
m_holdingThreadId.Clear();
dbg_LeaveLock();
#endif
{
VolatileStore(&m_lock, (LONG)0);
}
DECTHREADLOCKCOUNTTHREAD(pThread);
EE_LOCK_RELEASED(this);
} // SpinLock::FreeLock ()
//----------------------------------------------------------------------------
// SpinLock::SpinToAcquire , non-inline function, called from inline Acquire
//
// Spin waiting for a spinlock to become free.
//
//
void
SpinLock::SpinToAcquire()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
CAN_TAKE_LOCK;
SO_TOLERANT;
}
CONTRACTL_END;
DWORD backoffs = 0;
ULONG ulSpins = 0;
while (true)
{
for (unsigned i = ulSpins+10000;
ulSpins < i;
ulSpins++)
{
// Note: Must use Volatile to ensure the lock is
// refetched from memory.
//
if (VolatileLoad(&m_lock) == 0)
{
break;
}
YieldProcessor(); // indicate to the processor that we are spining
}
// Try the inline atomic test again.
//
if (GetLockNoWait())
{
// EE_LOCK_TAKEN(this) has already been called by GetLockNoWait
break;
}
//backoff
__SwitchToThread(0, backoffs++);
}
#ifdef _DEBUG
//profile info
SpinLockProfiler::IncrementCollisions (m_LockType);
SpinLockProfiler::IncrementSpins (m_LockType, ulSpins);
SpinLockProfiler::IncrementBackoffs (backoffs);
#endif
} // SpinLock::SpinToAcquire ()
#ifdef _DEBUG
// If a GC is not allowed when we enter the lock, we'd better not do anything inside
// the lock that could provoke a GC. Otherwise other threads attempting to block
// (which are presumably in the same GC mode as this one) will block. This will cause
// a deadlock if we do attempt a GC because we can't suspend blocking threads and we
// can't release the spin lock.
void SpinLock::dbg_PreEnterLock()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
Thread* pThread = GetThread();
if (pThread)
{
// SpinLock can not be nested.
_ASSERTE ((pThread->m_StateNC & Thread::TSNC_OwnsSpinLock) == 0);
pThread->SetThreadStateNC(Thread::TSNC_OwnsSpinLock);
if (!pThread->PreemptiveGCDisabled())
_ASSERTE(!m_requireCoopGCMode);
}
}
void SpinLock::dbg_EnterLock()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
Thread* pThread = GetThread();
if (pThread)
{
INCONTRACT(pThread->BeginNoTriggerGC(__FILE__, __LINE__));
}
}
void SpinLock::dbg_LeaveLock()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
Thread* pThread = GetThread();
if (pThread)
{
_ASSERTE ((pThread->m_StateNC & Thread::TSNC_OwnsSpinLock) != 0);
pThread->ResetThreadStateNC(Thread::TSNC_OwnsSpinLock);
INCONTRACT(pThread->EndNoTriggerGC());
}
}
void SpinLockProfiler::InitStatics ()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
s_ulBackOffs = 0;
memset (s_ulCollisons, 0, sizeof (s_ulCollisons));
memset (s_ulSpins, 0, sizeof (s_ulSpins));
}
void SpinLockProfiler::IncrementSpins (LOCK_TYPE type, ULONG value)
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
_ASSERTE(type <= LOCK_TYPE_DEFAULT);
s_ulSpins [type] += value;
}
void SpinLockProfiler::IncrementCollisions (LOCK_TYPE type)
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
++s_ulCollisons [type];
}
void SpinLockProfiler::IncrementBackoffs (ULONG value)
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
s_ulBackOffs += value;
}
void SpinLockProfiler::DumpStatics()
{
CONTRACTL
{
NOTHROW;
GC_NOTRIGGER;
DEBUG_ONLY;
}
CONTRACTL_END;
//<TODO>todo </TODO>
}
#endif // _DEBUG
// End of file: spinlock.cpp
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