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/*
* Copyright 2011, Ben Langmead <blangmea@jhsph.edu>
*
* This file is part of Bowtie 2.
*
* Bowtie 2 is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* Bowtie 2 is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Bowtie 2. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef SPINLOCK_H_
#define SPINLOCK_H_
/**
* This non-reentrant spinlock implementation for i386 and x86_64 is
* based on free code by Gert Boddaert:
*
* http://www.codeproject.com/KB/threads/spinlocks.aspx
*
* Using spinlocks instead of the heavier pthreads mutexes can, in some
* cases, help Bowtie perform better for large numbers of threads.
*/
// (If the user hasn't specified this, then there's no need for any
// kind of locking, so we skip this header)
#ifdef BOWTIE_PTHREADS
#if defined(__GNUC__)
#if defined(__x86_64__) || defined(__i386__)
#define USE_SPINLOCK
#endif
#endif
#ifdef USE_SPINLOCK
#if defined(__x86_64__)
#define SPINLOCK_WORD long
#else
#define SPINLOCK_WORD int
#endif
class SpinLock {
public: // inlined constructor
// inlined NON-virtual destructor
inline SpinLock() : m_s(1) {}
inline ~SpinLock() {}
// enter the lock, spinlocks (with/without Sleep)
// when mutex is already locked
inline void Enter(void)
{
SPINLOCK_WORD prev_s;
do
{
prev_s = TestAndSet(&m_s, 0);
if (m_s == 0 && prev_s == 1)
{
// The lock and was unlocked and we grabbed it
break;
}
// reluinquish current timeslice (can only
// be used when OS available and
// we do NOT want to 'spin')
// HWSleep(0);
}
while (true);
}
// Tries to enter the lock, returns 0
// when mutex is already locked,
// returns != 0 when success
inline int TryEnter(void)
{
SPINLOCK_WORD prev_s = TestAndSet(&m_s, 0);
if (m_s == 0 && prev_s == 1)
{
return 1;
}
return 0;
}
// Leaves or unlocks the mutex
// (should only be called by lock owner)
inline void Leave(void)
{
TestAndSet(&m_s, 1);
}
protected:
// sets BIT value and returns previous
// value.in 1 atomic un-interruptable operation
SPINLOCK_WORD TestAndSet(SPINLOCK_WORD* pTargetAddress, SPINLOCK_WORD nValue);
private:
SPINLOCK_WORD m_s;
};
// This part is Platform dependent!
/* The following piece of code can be found
in function AtomicExchange of file atomicops-internals-x86.h
under http://google-perftools.googlecode.com/svn/trunk/src/base/
*/
#if defined(__x86_64__)
#define TAS(_lw, _res) \
asm volatile("xchgq %1,%0":"=r"(_res):"m"(*_lw),"0"(_res):"memory")
#elif defined(__i386__)
#define TAS(_lw, _res) \
asm volatile("xchgl %1,%0":"=r"(_res):"m"(*_lw),"0"(_res):"memory")
#else
#error "Architecture is neither x86_64 nor i386 (see spinlock.h)"
#endif
/* TAS is only defined for GNUC on x86_64 and i386,
that is where GNUC x86 inline assembly can be used */
inline SPINLOCK_WORD SpinLock::TestAndSet(SPINLOCK_WORD* pTargetAddress, SPINLOCK_WORD nValue) {
#if 0
__asm
{
mov edx, dword ptr [pTargetAddress]
mov eax, nValue
lock xchg eax, dword ptr [edx]
}
#else
TAS(pTargetAddress, nValue);
return nValue;
#endif
// mov = 1 CPU cycle
// lock = 1 CPU cycle
// xchg = 3 CPU cycles
}
#endif /*USE_SPINLOCK*/
#endif /*BOWTIE_PTHREADS*/
#endif /*SPINLOCK_H_*/
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