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/*
* Copyright 2003-2020 The Music Player Daemon Project
* http://www.musicpd.org
*
* This program 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 2 of the License, or
* (at your option) any later version.
*
* 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/** \file
*
* Support for locking data structures from the database, for safe
* multi-threading.
*/
#ifndef MPD_DB_LOCK_HXX
#define MPD_DB_LOCK_HXX
#include "thread/Mutex.hxx"
#include "util/Compiler.h"
#include <cassert>
extern Mutex db_mutex;
#ifndef NDEBUG
#include "thread/Id.hxx"
extern ThreadId db_mutex_holder;
/**
* Does the current thread hold the database lock?
*/
gcc_pure
static inline bool
holding_db_lock() noexcept
{
return db_mutex_holder.IsInside();
}
#endif
/**
* Obtain the global database lock. This is needed before
* dereferencing a #song or #directory. It is not recursive.
*/
static inline void
db_lock(void)
{
assert(!holding_db_lock());
db_mutex.lock();
assert(db_mutex_holder.IsNull());
#ifndef NDEBUG
db_mutex_holder = ThreadId::GetCurrent();
#endif
}
/**
* Release the global database lock.
*/
static inline void
db_unlock(void)
{
assert(holding_db_lock());
#ifndef NDEBUG
db_mutex_holder = ThreadId::Null();
#endif
db_mutex.unlock();
}
class ScopeDatabaseLock {
bool locked = true;
public:
ScopeDatabaseLock() {
db_lock();
}
~ScopeDatabaseLock() {
if (locked)
db_unlock();
}
/**
* Unlock the mutex now, making the destructor a no-op.
*/
void unlock() {
assert(locked);
db_unlock();
locked = false;
}
};
/**
* Unlock the database while in the current scope.
*/
class ScopeDatabaseUnlock {
public:
ScopeDatabaseUnlock() {
db_unlock();
}
~ScopeDatabaseUnlock() {
db_lock();
}
};
#endif
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