// snapshots.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::kDefault

#include "mongo/platform/basic.h"

#include "mongo/db/stats/snapshots.h"

#include "mongo/base/static_assert.h"
#include "mongo/db/client.h"
#include "mongo/db/clientcursor.h"
#include "mongo/db/service_context.h"
#include "mongo/util/concurrency/idle_thread_block.h"
#include "mongo/util/exit.h"
#include "mongo/util/log.h"

/**
   handles snapshotting performance metrics and other such things
 */
namespace mongo {

using std::unique_ptr;
using std::endl;

void SnapshotData::takeSnapshot() {
    _created = curTimeMicros64();
    Top::get(getGlobalServiceContext()).cloneMap(_usage);
}

SnapshotDelta::SnapshotDelta(const SnapshotData& older, const SnapshotData& newer)
    : _older(older), _newer(newer) {
    verify(_newer._created > _older._created);
    _elapsed = _newer._created - _older._created;
}

Top::UsageMap SnapshotDelta::collectionUsageDiff() {
    verify(_newer._created > _older._created);
    Top::UsageMap u;

    for (Top::UsageMap::const_iterator i = _newer._usage.begin(); i != _newer._usage.end(); ++i) {
        Top::UsageMap::const_iterator j = _older._usage.find(i->first);
        if (j != _older._usage.end())
            u[i->first] = Top::CollectionData(j->second, i->second);
        else
            u[i->first] = i->second;
    }
    return u;
}

Snapshots::Snapshots() : _loc(0), _stored(0) {}

const SnapshotData* Snapshots::takeSnapshot() {
    stdx::lock_guard<stdx::mutex> lk(_lock);
    _loc = (_loc + 1) % kNumSnapshots;
    _snapshots[_loc].takeSnapshot();
    if (_stored < kNumSnapshots)
        _stored++;
    return &_snapshots[_loc];
}

StatusWith<SnapshotDiff> Snapshots::computeDelta() {
    stdx::lock_guard<stdx::mutex> lk(_lock);

    // We need 2 snapshots to calculate a delta
    if (_stored < 2) {
        return StatusWith<SnapshotDiff>(ErrorCodes::BadValue, "Less than 2 snapshots exist");
    }

    // The following logic depends on there being exactly 2 stored snapshots
    MONGO_STATIC_ASSERT(kNumSnapshots == 2);

    // Current and previous napshot alternates between indexes 0 and 1
    int currIdx = _loc;
    int prevIdx = _loc > 0 ? 0 : 1;
    SnapshotDelta delta(_snapshots[prevIdx], _snapshots[currIdx]);

    return SnapshotDiff(delta.collectionUsageDiff(), delta.elapsed());
}

void StatsSnapshotThread::run() {
    Client::initThread("statsSnapshot");
    while (!inShutdown()) {
        try {
            statsSnapshots.takeSnapshot();
        } catch (std::exception& e) {
            log() << "ERROR in SnapshotThread: " << redact(e.what()) << endl;
        }

        MONGO_IDLE_THREAD_BLOCK;
        sleepsecs(4);
    }
}

Snapshots statsSnapshots;
StatsSnapshotThread statsSnapshotThread;
}
