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// spin_lock.cpp
/* Copyright 2009 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/>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the GNU Affero General Public License in all respects
* for all of the code used other than as permitted herein. If you modify
* file(s) with this exception, you may extend this exception to your
* version of the file(s), but you are not obligated to do so. If you do not
* wish to do so, delete this exception statement from your version. If you
* delete this exception statement from all source files in the program,
* then also delete it in the license file.
*/
#include "mongo/pch.h" // todo eliminate this include
#include "mongo/util/concurrency/spin_lock.h"
#include <time.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
#if defined(__USE_XOPEN2K)
NOINLINE_DECL void SpinLock::_lk() {
/**
* 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
*/
for ( int i=0; i<1000; i++ ) {
if ( pthread_spin_trylock( &_lock ) == 0 )
return;
#if defined(__i386__) || defined(__x86_64__)
asm volatile ( "pause" ) ; // maybe trylock does this; just in case.
#endif
}
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)
void SpinLock::lock() {
// fast path
if (!_locked && !__sync_lock_test_and_set(&_locked, true)) {
return;
}
// wait for lock
int wait = 1000;
while ((wait-- > 0) && (_locked)) {
#if defined(__i386__) || defined(__x86_64__)
asm volatile ( "pause" ) ;
#endif
}
// 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);
}
}
#endif
bool SpinLock::isfast() {
#if defined(_WIN32) || defined(__USE_XOPEN2K) || defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4)
return true;
#else
return false;
#endif
}
} // namespace mongo
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