// shardconnection.cpp

/**
*    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/>.
*
*    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.
*/

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kSharding

#define MONGO_PCH_WHITELISTED
#include "mongo/platform/basic.h"
#include "mongo/pch.h"
#undef MONGO_PCH_WHITELISTED

#include <boost/noncopyable.hpp>
#include <set>

#include "mongo/db/auth/authorization_manager.h"
#include "mongo/db/client.h"
#include "mongo/db/commands.h"
#include "mongo/db/lasterror.h"
#include "mongo/db/server_parameters.h"
#include "mongo/s/config.h"
#include "mongo/s/request.h"
#include "mongo/s/shard.h"
#include "mongo/s/stale_exception.h"
#include "mongo/s/version_manager.h"
#include "mongo/server.h"
#include "mongo/util/concurrency/spin_lock.h"
#include "mongo/util/exit.h"
#include "mongo/util/log.h"
#include "mongo/util/stacktrace.h"

namespace mongo {

    using std::auto_ptr;
    using std::endl;
    using std::map;
    using std::set;
    using std::string;
    using std::stringstream;
    using std::vector;

    DBConnectionPool shardConnectionPool;

    class ClientConnections;

    /**
     * Class which tracks ClientConnections (the client connection pool) for each incoming
     * connection, allowing stats access.
     */

    class ActiveClientConnections {
     public:

        ActiveClientConnections() : _mutex( "ActiveClientConnections" ) {
        }

        void add( const ClientConnections* cc ) {
            scoped_lock lock( _mutex );
            _clientConnections.insert( cc );
        }

        void remove( const ClientConnections* cc ) {
            scoped_lock lock( _mutex );
            _clientConnections.erase( cc );
        }

        // Implemented after ClientConnections
        void appendInfo( BSONObjBuilder& b );

    private:
        mongo::mutex _mutex;
        set<const ClientConnections*> _clientConnections;

    } activeClientConnections;

    /**
     * Command to allow access to the sharded conn pool information in mongos.
     * TODO: Refactor with other connection pooling changes
     */
    class ShardedPoolStats : public Command {
    public:

        ShardedPoolStats() : Command( "shardConnPoolStats" ) {}
        virtual void help( stringstream &help ) const { help << "stats about the shard connection pool"; }
        virtual bool isWriteCommandForConfigServer() const { return false; }
        virtual bool slaveOk() const { return true; }

        // Same privs as connPoolStats
        virtual void addRequiredPrivileges( const std::string& dbname,
                                            const BSONObj& cmdObj,
                                            std::vector<Privilege>* out )
        {
            ActionSet actions;
            actions.addAction( ActionType::connPoolStats );
            out->push_back( Privilege( ResourcePattern::forClusterResource(), actions ) );
        }

        virtual bool run( OperationContext* txn, const string&, mongo::BSONObj&, int, std::string&, mongo::BSONObjBuilder& result, bool ) {
            // Base pool info
            shardConnectionPool.appendInfo( result );
            // Thread connection info
            activeClientConnections.appendInfo( result );
            return true;
        }

    } shardedPoolStatsCmd;

    /**
     * holds all the actual db connections for a client to various servers
     * 1 per thread, so doesn't have to be thread safe
     */
    class ClientConnections : boost::noncopyable {
    public:
        struct Status : boost::noncopyable {
            Status() : created(0), avail(0) {}

            // May be read concurrently, but only written from
            // this thread.
            long long created;
            DBClientBase* avail;
        };

        // Gets or creates the status object for the host
        Status* _getStatus( const string& addr ) {
            scoped_spinlock lock( _lock );
            Status* &temp = _hosts[addr];
            if ( ! temp )
                temp = new Status();
            return temp;
        }

        ClientConnections() {
            // Start tracking client connections
            activeClientConnections.add( this );
        }

        ~ClientConnections() {
            // Stop tracking these client connections
            activeClientConnections.remove( this );

            releaseAll( true );
        }

        void releaseAll( bool fromDestructor = false ) {

            // Don't need spinlock protection because if not in the destructor, we don't 
            // modify _hosts, and if in the destructor we are not accessible to external
            // threads.

            for ( HostMap::iterator i=_hosts.begin(); i!=_hosts.end(); ++i ) {
                string addr = i->first;
                Status* ss = i->second;
                verify( ss );
                if ( ss->avail ) {
                    /* if we're shutting down, don't want to initiate release mechanism as it is slow,
                       and isn't needed since all connections will be closed anyway */
                    if ( inShutdown() ) {
                        if( versionManager.isVersionableCB( ss->avail ) ) versionManager.resetShardVersionCB( ss->avail );
                        delete ss->avail;
                    }
                    else
                        release( addr , ss->avail );
                    ss->avail = 0;
                }
                if ( fromDestructor ) delete ss;
            }
            if ( fromDestructor ) _hosts.clear();
        }

        DBClientBase * get( const string& addr , const string& ns ) {

            {
                // We want to report ns stats
                scoped_spinlock lock(_lock);
                if (ns.size() > 0)
                    _seenNS.insert(ns);
            }

            Status* s = _getStatus( addr );

            auto_ptr<DBClientBase> c; // Handles cleanup if there's an exception thrown
            if ( s->avail ) {
                c.reset( s->avail );
                s->avail = 0;
                shardConnectionPool.onHandedOut( c.get() ); // May throw an exception
            } else {
                c.reset( shardConnectionPool.get( addr ) );
                s->created++; // After, so failed creation doesn't get counted
            }
            return c.release();
        }

        void done( const string& addr , DBClientBase* conn ) {
            Status* s = _hosts[addr];
            verify( s );

            const bool isConnGood = shardConnectionPool.isConnectionGood(addr, conn);

            if (s->avail != NULL) {
                warning() << "Detected additional sharded connection in the "
                        "thread local pool for " << addr << endl;

                if (DBException::traceExceptions) {
                    // There shouldn't be more than one connection checked out to the same
                    // host on the same thread.
                    printStackTrace();
                }

                if (!isConnGood) {
                    delete s->avail;
                    s->avail = NULL;
                }

                // Let the internal pool handle the bad connection, this can also
                // update the lower bounds for the known good socket creation time
                // for this host.
                release(addr, conn);
                return;
            }

            if (!isConnGood) {
                // Let the internal pool handle the bad connection.
                release(addr, conn);
                return;
            }

            // Note: Although we try our best to clear bad connections as much as possible,
            // some of them can still slip through because of how ClientConnections are being
            // used - as thread local variables. This means that threads won't be able to
            // see the s->avail connection of other threads.

            s->avail = conn;
        }

        void sync() {
            for ( HostMap::iterator i=_hosts.begin(); i!=_hosts.end(); ++i ) {
                string addr = i->first;
                Status* ss = i->second;
                if ( ss->avail )
                    ss->avail->getLastError();
                
            }
        }

        void checkVersions( const string& ns ) {

            vector<Shard> all;
            Shard::getAllShards( all );

            // Don't report exceptions here as errors in GetLastError
            LastError::Disabled ignoreForGLE(lastError.get(false));

            // Now only check top-level shard connections
            for ( unsigned i=0; i<all.size(); i++ ) {

                Shard& shard = all[i];
                try {
                    string sconnString = shard.getConnString();
                    Status* s = _getStatus( sconnString );

                    if( ! s->avail ) {
                        s->avail = shardConnectionPool.get( sconnString );
                        s->created++; // After, so failed creation doesn't get counted
                    }

                    versionManager.checkShardVersionCB( s->avail, ns, false, 1 );
                }
                catch ( const DBException& ex ) {

                    warning() << "problem while initially checking shard versions on" << " "
                              << shard.getName() << causedBy( ex ) << endl;

                    // NOTE: This is only a heuristic, to avoid multiple stale version retries
                    // across multiple shards, and does not affect correctness.
                }
            }
        }

        void release( const string& addr , DBClientBase * conn ) {
            shardConnectionPool.release( addr , conn );
        }

        /**
         * Appends info about the client connection pool to a BOBuilder
         * Safe to call with activeClientConnections lock
         */
        void appendInfo( BSONObjBuilder& b ) const {

            scoped_spinlock lock( _lock );

            BSONArrayBuilder hostsArrB( b.subarrayStart( "hosts" ) );
            for ( HostMap::const_iterator i = _hosts.begin(); i != _hosts.end(); ++i ) {
                BSONObjBuilder bb( hostsArrB.subobjStart() );
                bb.append( "host", i->first );
                bb.append( "created", i->second->created );
                bb.appendBool( "avail", static_cast<bool>( i->second->avail ) );
                bb.done();
            }
            hostsArrB.done();

            BSONArrayBuilder nsArrB( b.subarrayStart( "seenNS" ) );
            for ( set<string>::const_iterator i = _seenNS.begin(); i != _seenNS.end(); ++i ) {
                nsArrB.append(*i);
            }
            nsArrB.done();
        }
        
        // Protects only the creation of new entries in the _hosts and _seenNS map
        // from external threads.  Reading _hosts / _seenNS in this thread doesn't
        // need protection.
        mutable SpinLock _lock;
        typedef map<string,Status*,DBConnectionPool::serverNameCompare> HostMap;
        HostMap _hosts;
        set<string> _seenNS;

        /**
         * Clears the connections kept by this pool (ie, not including the global pool)
         */
        void clearPool() {
            for(HostMap::iterator iter = _hosts.begin(); iter != _hosts.end(); ++iter) {
                if (iter->second->avail != NULL) {
                    delete iter->second->avail;
                }
                delete iter->second;
            }

            _hosts.clear();
        }

        void forgetNS( const string& ns ) {
            scoped_spinlock lock( _lock );
            _seenNS.erase( ns );
        }

        // -----

        static thread_specific_ptr<ClientConnections> _perThread;

        static ClientConnections* threadInstance() {
            ClientConnections* cc = _perThread.get();
            if ( ! cc ) {
                cc = new ClientConnections();
                _perThread.reset( cc );
            }
            return cc;
        }
    };

    thread_specific_ptr<ClientConnections> ClientConnections::_perThread;

    /**
     * Appends info about all active client shard connections to a BOBuilder
     */
    void ActiveClientConnections::appendInfo( BSONObjBuilder& b ) {

        BSONArrayBuilder arr( 64 * 1024 ); // There may be quite a few threads

        {
            scoped_lock lock( _mutex );
            for ( set<const ClientConnections*>::const_iterator i = _clientConnections.begin();
                  i != _clientConnections.end(); ++i )
            {
                BSONObjBuilder bb( arr.subobjStart() );
                (*i)->appendInfo( bb );
                bb.done();
            }
        }

        b.appendArray( "threads", arr.obj() );
    }

    ShardConnection::ShardConnection( const Shard * s , const string& ns, ChunkManagerPtr manager )
        : _addr( s->getConnString() ) , _ns( ns ), _manager( manager ) {
        _init();
    }

    ShardConnection::ShardConnection( const Shard& s , const string& ns, ChunkManagerPtr manager )
        : _addr( s.getConnString() ) , _ns( ns ), _manager( manager ) {
        _init();
    }

    ShardConnection::ShardConnection( const string& addr , const string& ns, ChunkManagerPtr manager )
        : _addr( addr ) , _ns( ns ), _manager( manager ) {
        _init();
    }

    void usingAShardConnection( const string& addr );

    void ShardConnection::_init() {
        verify( _addr.size() );
        _conn = ClientConnections::threadInstance()->get( _addr , _ns );
        _finishedInit = false;
        usingAShardConnection( _addr );
    }

    void ShardConnection::_finishInit() {
        if ( _finishedInit )
            return;
        _finishedInit = true;

        if (versionManager.isVersionableCB(_conn)) {
            // Make sure we specified a manager for the correct namespace
            if (_ns.size() && _manager)
                verify(_manager->getns() == _ns);
            _setVersion = versionManager.checkShardVersionCB( this , false , 1 );
        }
        else {
            // Make sure we didn't specify a manager for a non-versionable connection (i.e. config)
            verify(!_manager);
            _setVersion = false;
        }
    }

    void ShardConnection::done() {
        if ( _conn ) {
            ClientConnections::threadInstance()->done( _addr , _conn );
            _conn = 0;
            _finishedInit = true;
        }
    }

    void ShardConnection::kill() {
        if ( _conn ) {
            if( versionManager.isVersionableCB( _conn ) ) versionManager.resetShardVersionCB( _conn );

            if (_conn->isFailed()) {
                // Let the pool know about the bad connection and also delegate disposal to it.
                ClientConnections::threadInstance()->done(_addr, _conn);
            }
            else {
                delete _conn;
            }

            _conn = 0;
            _finishedInit = true;
        }
    }

    void ShardConnection::sync() {
        ClientConnections::threadInstance()->sync();
    }

    void ShardConnection::checkMyConnectionVersions( const string & ns ) {
        ClientConnections::threadInstance()->checkVersions( ns );
    }

    ShardConnection::~ShardConnection() {
        if ( _conn ) {
            if (_conn->isFailed()) {
                if (_conn->getSockCreationMicroSec() ==
                        DBClientBase::INVALID_SOCK_CREATION_TIME) {
                    kill();
                }
                else {
                    // The pool takes care of deleting the failed connection - this
                    // will also trigger disposal of older connections in the pool
                    done();
                }
            }
            else {
                /* see done() comments above for why we log this line */
                log() << "sharded connection to " << _conn->getServerAddress()
                        << " not being returned to the pool" << endl;

                kill();
            }
        }
    }

    void ShardConnection::releaseMyConnections() {
        ClientConnections::threadInstance()->releaseAll();
    }

    void ShardConnection::clearPool() {
        shardConnectionPool.clear();
        ClientConnections::threadInstance()->clearPool();
    }

    void ShardConnection::forgetNS( const string& ns ) {
        ClientConnections::threadInstance()->forgetNS( ns );
    }
}