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/* @file value.h
concurrency helpers DiagStr, Guarded
*/
/**
* 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,b
* 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
#include "mutex.h"
namespace mongo {
/** declare that a variable that is "guarded" by a mutex.
The decl documents the rule. For example "counta and countb are guarded by xyzMutex":
Guarded<int, xyzMutex> counta;
Guarded<int, xyzMutex> countb;
Upon use, specify the scoped_lock object. This makes it hard for someone
later to forget to be in the lock. Check is made that it is the right lock in _DEBUG
builds at runtime.
*/
template <typename T, mutex& BY>
class Guarded : boost::noncopyable {
T _val;
public:
T& ref(const scoped_lock& lk) {
dassert( lk._mut == &BY );
return _val;
}
};
class DiagStr {
string _s;
static SimpleMutex m;
public:
DiagStr(const DiagStr& r) : _s(r.get()) { }
DiagStr() { }
bool empty() const {
SimpleMutex::scoped_lock lk(m);
return _s.empty();
}
string get() const {
SimpleMutex::scoped_lock lk(m);
return _s;
}
void set(const char *s) {
SimpleMutex::scoped_lock lk(m);
_s = s;
}
void set(const string& s) {
SimpleMutex::scoped_lock lk(m);
_s = s;
}
operator string() const { return get(); }
void operator=(const string& s) { set(s); }
void operator=(const DiagStr& rhs) {
SimpleMutex::scoped_lock lk(m);
_s = rhs.get();
}
};
#if 0 // not including in 2.0
/** Thread safe map.
Be careful not to use this too much or it could make things slow;
if not a hot code path no problem.
Examples:
mapsf<int,int> mp;
int x = mp.get();
map<int,int> two;
mp.swap(two);
{
mapsf<int,int>::ref r(mp);
r[9] = 1;
map<int,int>::iterator i = r.r.begin();
}
*/
template< class K, class V >
struct mapsf : boost::noncopyable {
SimpleMutex m;
map<K,V> val;
friend struct ref;
public:
mapsf() : m("mapsf") { }
void swap(map<K,V>& rhs) {
SimpleMutex::scoped_lock lk(m);
val.swap(rhs);
}
// safe as we pass by value:
V get(K k) {
SimpleMutex::scoped_lock lk(m);
map<K,V>::iterator i = val.find(k);
if( i == val.end() )
return K();
return i->second;
}
// think about deadlocks when using ref. the other methods
// above will always be safe as they are "leaf" operations.
struct ref {
SimpleMutex::scoped_lock lk;
public:
map<K,V> const &r;
ref(mapsf<K,V> &m) : lk(m.m), r(m.val) { }
V& operator[](const K& k) { return r[k]; }
};
};
#endif
}
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