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// list.h
/**
* Copyright (C) 2008 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/>.
*/
#pragma once
namespace mongo {
/* this class uses a mutex for writes, but not for reads.
we can get fancier later...
struct Member : public List1<Member>::Base {
const char *host;
int port;
};
List1<Member> _members;
_members.head()->next();
*/
template<typename T>
class List1 : boost::noncopyable {
public:
/* next() and head() return 0 at end of list */
List1() : _head(0), _m("List1"), _orphans(0) { }
class Base {
friend class List1;
T *_next;
public:
Base() : _next(0){}
~Base() { wassert(false); } // we never want this to happen
T* next() const { return _next; }
};
/** note this is safe:
T* p = mylist.head();
if( p )
use(p);
and this is not:
if( mylist.head() )
use( mylist.head() ); // could become 0
*/
T* head() const { return (T*) _head; }
void push(T* t) {
assert( t->_next == 0 );
scoped_lock lk(_m);
t->_next = (T*) _head;
_head = t;
}
// intentionally leaks.
void orphanAll() {
scoped_lock lk(_m);
_head = 0;
}
/* t is not deleted, but is removed from the list. (orphaned) */
void orphan(T* t) {
scoped_lock lk(_m);
T *&prev = (T*&) _head;
T *n = prev;
while( n != t ) {
uassert( 14050 , "List1: item to orphan not in list", n );
prev = n->_next;
n = prev;
}
prev = t->_next;
if( ++_orphans > 500 )
log() << "warning List1 orphans=" << _orphans << '\n';
}
private:
volatile T *_head;
mongo::mutex _m;
int _orphans;
};
};
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