128 lines
3.4 KiB
C++
128 lines
3.4 KiB
C++
// spin_lock.cpp
|
|
|
|
/**
|
|
* Copyright (C) 2010 10gen Inc.
|
|
*
|
|
* This program is free software: you can redistribute it and/or modify
|
|
* it under the terms of the GNU Affero General Public License, version 3,
|
|
* as published by the Free Software Foundation.
|
|
*
|
|
* This program 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 Affero General Public License for more details.
|
|
*
|
|
* You should have received a copy of the GNU Affero General Public License
|
|
* along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
*/
|
|
|
|
#include "pch.h"
|
|
#include <time.h>
|
|
#include "spin_lock.h"
|
|
|
|
namespace mongo {
|
|
|
|
SpinLock::~SpinLock() {
|
|
#if defined(_WIN32)
|
|
DeleteCriticalSection(&_cs);
|
|
#elif defined(__USE_XOPEN2K)
|
|
pthread_spin_destroy(&_lock);
|
|
#endif
|
|
}
|
|
|
|
SpinLock::SpinLock()
|
|
#if defined(_WIN32)
|
|
{ InitializeCriticalSectionAndSpinCount(&_cs, 4000); }
|
|
#elif defined(__USE_XOPEN2K)
|
|
{ pthread_spin_init( &_lock , 0 ); }
|
|
#elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
|
|
: _locked( false ) { }
|
|
#else
|
|
: _mutex( "SpinLock" ) { }
|
|
#endif
|
|
|
|
void SpinLock::lock() {
|
|
#if defined(_WIN32)
|
|
EnterCriticalSection(&_cs);
|
|
#elif defined(__USE_XOPEN2K)
|
|
|
|
/**
|
|
* this is designed to perform close to the default spin lock
|
|
* the reason for the mild insanity is to prevent horrible performance
|
|
* when contention spikes
|
|
* it allows spinlocks to be used in many more places
|
|
* which is good because even with this change they are about 8x faster on linux
|
|
*/
|
|
|
|
if ( pthread_spin_trylock( &_lock ) == 0 )
|
|
return;
|
|
|
|
for ( int i=0; i<1000; i++ )
|
|
if ( pthread_spin_trylock( &_lock ) == 0 )
|
|
return;
|
|
|
|
for ( int i=0; i<1000; i++ ) {
|
|
if ( pthread_spin_trylock( &_lock ) == 0 )
|
|
return;
|
|
pthread_yield();
|
|
}
|
|
|
|
struct timespec t;
|
|
t.tv_sec = 0;
|
|
t.tv_nsec = 5000000;
|
|
|
|
while ( pthread_spin_trylock( &_lock ) != 0 ) {
|
|
nanosleep(&t, NULL);
|
|
}
|
|
|
|
#elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
|
|
// fast path
|
|
if (!_locked && !__sync_lock_test_and_set(&_locked, true)) {
|
|
return;
|
|
}
|
|
|
|
// wait for lock
|
|
int wait = 1000;
|
|
while ((wait-- > 0) && (_locked)) {}
|
|
|
|
// if failed to grab lock, sleep
|
|
struct timespec t;
|
|
t.tv_sec = 0;
|
|
t.tv_nsec = 5000000;
|
|
while (__sync_lock_test_and_set(&_locked, true)) {
|
|
nanosleep(&t, NULL);
|
|
}
|
|
#else
|
|
// WARNING Missing spin lock in this platform. This can potentially
|
|
// be slow.
|
|
_mutex.lock();
|
|
|
|
#endif
|
|
}
|
|
|
|
void SpinLock::unlock() {
|
|
#if defined(_WIN32)
|
|
LeaveCriticalSection(&_cs);
|
|
#elif defined(__USE_XOPEN2K)
|
|
pthread_spin_unlock(&_lock);
|
|
#elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
|
|
__sync_lock_release(&_locked);
|
|
#else
|
|
_mutex.unlock();
|
|
#endif
|
|
}
|
|
|
|
bool SpinLock::isfast() {
|
|
#if defined(_WIN32)
|
|
return true;
|
|
#elif defined(__USE_XOPEN2K)
|
|
return true;
|
|
#elif defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
|
|
return true;
|
|
#else
|
|
return false;
|
|
#endif
|
|
}
|
|
|
|
|
|
} // namespace mongo
|