/
lock.h
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/
lock.h
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/*
* Copyright 2009, Pythia authors (see AUTHORS file).
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* 3. Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef __MYLOCK__
#define __MYLOCK__
/**
* Non-recursive spinlock. Using `xchg` and `ldstub` as in PostgresSQL.
*/
class Lock {
public:
Lock() : _l(0) { }
/** Call blocks and retunrs only when it has the lock. */
inline void lock()
{
while(tas(&_l)) {
#if defined(__i386__) || defined(__x86_64__)
__asm__ __volatile__ ("pause\n");
#endif
}
}
/** Unlocks the lock object. */
inline void unlock()
{
_l = 0;
}
/** Resets lock, guaranteed to be called non-concurrently. */
inline void reset()
{
unlock();
}
private:
inline int tas(volatile char* lock)
{
register char res = 1;
#if defined(__i386__) || defined(__x86_64__)
__asm__ __volatile__ (
"lock xchgb %0, %1\n"
: "+q"(res), "+m"(*lock)
:
: "memory", "cc");
#elif defined(__sparc__)
__asm__ __volatile__ (
"ldstub [%2], %0"
: "=r"(res), "+m"(*lock)
: "r"(lock)
: "memory");
#else
#error TAS not defined for this architecture.
#endif
return res;
}
volatile char _l;
};
#endif