/* @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"
#include "spin_lock.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;
        mutable SpinLock m;
    public:
        DiagStr(const DiagStr& r) : _s(r.get()) { }
        DiagStr() { }
        bool empty() const { 
            scoped_spinlock lk(m);
            return _s.empty();
        }
        string get() const { 
            scoped_spinlock lk(m);
            return _s;
        }

        void set(const char *s) {
            scoped_spinlock lk(m);
            _s = s;
        }
        void set(const string& s) { 
            scoped_spinlock lk(m);
            _s = s;
        }
        operator string() const { return get(); }
        void operator=(const string& s) { set(s); }
        void operator=(const DiagStr& rhs) { 
            scoped_spinlock 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
}