path: root/src/mongo/db/session_catalog.cpp

/**
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 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
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 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
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 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
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#define MONGO_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kWrite

#include "mongo/platform/basic.h"

#include "mongo/db/session_catalog.h"

#include <memory>

#include "mongo/db/service_context.h"
#include "mongo/logv2/log.h"

namespace mongo {
namespace {

const auto sessionTransactionTableDecoration = ServiceContext::declareDecoration<SessionCatalog>();

const auto operationSessionDecoration =
    OperationContext::declareDecoration<boost::optional<SessionCatalog::ScopedCheckedOutSession>>();

}  // namespace

SessionCatalog::~SessionCatalog() {
    stdx::lock_guard<Latch> lg(_mutex);
    for (const auto& entry : _sessions) {
        ObservableSession session(lg, entry.second->session);
        invariant(!session.currentOperation());
        invariant(!session._killed());
    }
}

void SessionCatalog::reset_forTest() {
    stdx::lock_guard<Latch> lg(_mutex);
    _sessions.clear();
}

SessionCatalog* SessionCatalog::get(OperationContext* opCtx) {
    return get(opCtx->getServiceContext());
}

SessionCatalog* SessionCatalog::get(ServiceContext* service) {
    auto& sessionTransactionTable = sessionTransactionTableDecoration(service);
    return &sessionTransactionTable;
}

SessionCatalog::ScopedCheckedOutSession SessionCatalog::_checkOutSession(OperationContext* opCtx) {
    // This method is not supposed to be called with an already checked-out session due to risk of
    // deadlock
    invariant(opCtx->getLogicalSessionId());
    invariant(!operationSessionDecoration(opCtx));
    invariant(!opCtx->lockState()->inAWriteUnitOfWork());
    invariant(!opCtx->lockState()->isLocked());

    stdx::unique_lock<Latch> ul(_mutex);
    uassert(ErrorCodes::InterruptedDueToReplStateChange,
            "a stepdown process started, can't checkout sessions except for killing",
            _checkoutAllowed);

    auto sri = _getOrCreateSessionRuntimeInfo(ul, opCtx, *opCtx->getLogicalSessionId());

    // Wait until the session is no longer checked out and until the previously scheduled kill has
    // completed
    ++sri->numWaitingToCheckOut;
    ON_BLOCK_EXIT([&] { --sri->numWaitingToCheckOut; });

    opCtx->waitForConditionOrInterrupt(sri->availableCondVar, ul, [&ul, &sri]() {
        ObservableSession osession(ul, sri->session);
        return !osession.currentOperation() && !osession._killed();
    });

    sri->session._checkoutOpCtx = opCtx;
    sri->session._lastCheckout = Date_t::now();

    return ScopedCheckedOutSession(
        *this, std::move(sri), boost::none /* Not checked out for kill */);
}

SessionCatalog::SessionToKill SessionCatalog::checkOutSessionForKill(OperationContext* opCtx,
                                                                     KillToken killToken) {
    // This method is not supposed to be called with an already checked-out session due to risk of
    // deadlock
    invariant(!operationSessionDecoration(opCtx));
    invariant(!opCtx->getTxnNumber());

    stdx::unique_lock<Latch> ul(_mutex);
    auto sri = _getOrCreateSessionRuntimeInfo(ul, opCtx, killToken.lsidToKill);
    invariant(ObservableSession(ul, sri->session)._killed());

    // Wait until the session is no longer checked out
    ++sri->numWaitingToCheckOut;
    ON_BLOCK_EXIT([&] { --sri->numWaitingToCheckOut; });

    opCtx->waitForConditionOrInterrupt(sri->availableCondVar, ul, [&ul, &sri] {
        ObservableSession osession(ul, sri->session);
        return !osession.currentOperation();
    });

    sri->session._checkoutOpCtx = opCtx;
    sri->session._lastCheckout = Date_t::now();

    return SessionToKill(ScopedCheckedOutSession(*this, std::move(sri), std::move(killToken)));
}

void SessionCatalog::scanSession(const LogicalSessionId& lsid,
                                 const ScanSessionsCallbackFn& workerFn) {
    std::unique_ptr<SessionRuntimeInfo> sessionToReap;

    {
        stdx::lock_guard<Latch> lg(_mutex);
        auto it = _sessions.find(lsid);
        if (it != _sessions.end()) {
            auto& sri = it->second;
            ObservableSession osession(lg, sri->session);
            workerFn(osession);

            if (osession._markedForReap && !osession._killed() && !osession.currentOperation() &&
                !sri->numWaitingToCheckOut) {
                sessionToReap = std::move(sri);
                _sessions.erase(it);
            }
        }
    }
}

void SessionCatalog::scanSessions(const SessionKiller::Matcher& matcher,
                                  const ScanSessionsCallbackFn& workerFn) {
    std::vector<std::unique_ptr<SessionRuntimeInfo>> sessionsToReap;

    {
        stdx::lock_guard<Latch> lg(_mutex);

        LOGV2_DEBUG(21976,
                    2,
                    "Scanning {sessionCount} sessions",
                    "Scanning sessions",
                    "sessionCount"_attr = _sessions.size());

        for (auto it = _sessions.begin(); it != _sessions.end(); ++it) {
            if (matcher.match(it->first)) {
                auto& sri = it->second;
                ObservableSession osession(lg, sri->session);

                workerFn(osession);

                if (osession._markedForReap && !osession._killed() &&
                    !osession.currentOperation() && !sri->numWaitingToCheckOut) {
                    sessionsToReap.emplace_back(std::move(sri));
                    _sessions.erase(it++);
                }
            }
        }
    }
}

void SessionCatalog::_disallowCheckoutsExceptForKilling() {
    stdx::unique_lock<Latch> ul(_mutex);
    _checkoutAllowed = false;
}

void SessionCatalog::_allowCheckouts() {
    stdx::lock_guard<Latch> lg(_mutex);
    _checkoutAllowed = true;
}

SessionCatalog::KillToken SessionCatalog::killSession(const LogicalSessionId& lsid) {
    stdx::lock_guard<Latch> lg(_mutex);
    auto it = _sessions.find(lsid);
    uassert(ErrorCodes::NoSuchSession, "Session not found", it != _sessions.end());

    auto& sri = it->second;
    return ObservableSession(lg, sri->session).kill();
}

size_t SessionCatalog::size() const {
    stdx::lock_guard<Latch> lg(_mutex);
    return _sessions.size();
}

SessionCatalog::SessionRuntimeInfo* SessionCatalog::_getOrCreateSessionRuntimeInfo(
    WithLock, OperationContext* opCtx, const LogicalSessionId& lsid) {
    auto it = _sessions.find(lsid);
    if (it == _sessions.end()) {
        it = _sessions.emplace(lsid, std::make_unique<SessionRuntimeInfo>(lsid)).first;
    }

    return it->second.get();
}

void SessionCatalog::_releaseSession(SessionRuntimeInfo* sri,
                                     boost::optional<KillToken> killToken) {
    stdx::lock_guard<Latch> lg(_mutex);

    // Make sure we have exactly the same session on the map and that it is still associated with an
    // operation context (meaning checked-out)
    invariant(_sessions[sri->session.getSessionId()].get() == sri);
    invariant(sri->session._checkoutOpCtx);
    sri->session._checkoutOpCtx = nullptr;
    sri->availableCondVar.notify_all();

    if (killToken) {
        invariant(sri->session._killsRequested > 0);
        --sri->session._killsRequested;
    }
}

SessionCatalog::SessionRuntimeInfo::~SessionRuntimeInfo() {
    invariant(!numWaitingToCheckOut);
}

SessionCatalog::KillToken ObservableSession::kill(ErrorCodes::Error reason) const {
    const bool firstKiller = (0 == _session->_killsRequested);
    ++_session->_killsRequested;

    // For currently checked-out sessions, interrupt the operation context so that the current owner
    // can release the session
    if (firstKiller && _session->_checkoutOpCtx) {
        invariant(_clientLock);
        const auto serviceContext = _session->_checkoutOpCtx->getServiceContext();
        serviceContext->killOperation(_clientLock, _session->_checkoutOpCtx, reason);
    }

    return SessionCatalog::KillToken(getSessionId());
}

void ObservableSession::markForReap() {
    _markedForReap = true;
}

bool ObservableSession::_killed() const {
    return _session->_killsRequested > 0;
}

OperationContextSession::OperationContextSession(OperationContext* opCtx) : _opCtx(opCtx) {
    auto& checkedOutSession = operationSessionDecoration(opCtx);
    if (checkedOutSession) {
        // The only case where a session can be checked-out more than once is due to DBDirectClient
        // reentrancy
        invariant(opCtx->getClient()->isInDirectClient());
        return;
    }

    checkOut(opCtx);
}

OperationContextSession::OperationContextSession(OperationContext* opCtx,
                                                 SessionCatalog::KillToken killToken)
    : _opCtx(opCtx) {
    auto& checkedOutSession = operationSessionDecoration(opCtx);

    invariant(!checkedOutSession);
    invariant(!opCtx->getLogicalSessionId());  // lsid is specified by killToken argument.

    const auto catalog = SessionCatalog::get(opCtx);
    auto scopedSessionForKill = catalog->checkOutSessionForKill(opCtx, std::move(killToken));

    // We acquire a Client lock here to guard the construction of this session so that references to
    // this session are safe to use while the lock is held
    stdx::lock_guard lk(*opCtx->getClient());
    checkedOutSession.emplace(std::move(scopedSessionForKill._scos));
}

OperationContextSession::~OperationContextSession() {
    // Only release the checked out session at the end of the top-level request from the client, not
    // at the end of a nested DBDirectClient call
    if (_opCtx->getClient()->isInDirectClient()) {
        return;
    }

    auto& checkedOutSession = operationSessionDecoration(_opCtx);
    if (!checkedOutSession)
        return;

    checkIn(_opCtx);
}

Session* OperationContextSession::get(OperationContext* opCtx) {
    auto& checkedOutSession = operationSessionDecoration(opCtx);
    if (checkedOutSession) {
        return checkedOutSession->get();
    }

    return nullptr;
}

void OperationContextSession::checkIn(OperationContext* opCtx) {
    auto& checkedOutSession = operationSessionDecoration(opCtx);
    invariant(checkedOutSession);

    // Removing the checkedOutSession from the OperationContext must be done under the Client lock,
    // but destruction of the checkedOutSession must not be, as it takes the SessionCatalog mutex,
    // and other code may take the Client lock while holding that mutex.
    stdx::unique_lock<Client> lk(*opCtx->getClient());
    SessionCatalog::ScopedCheckedOutSession sessionToReleaseOutOfLock(
        std::move(*checkedOutSession));

    // This destroys the moved-from ScopedCheckedOutSession, and must be done within the client lock
    checkedOutSession = boost::none;
    lk.unlock();
}

void OperationContextSession::checkOut(OperationContext* opCtx) {
    auto& checkedOutSession = operationSessionDecoration(opCtx);
    invariant(!checkedOutSession);

    const auto catalog = SessionCatalog::get(opCtx);
    auto scopedCheckedOutSession = catalog->_checkOutSession(opCtx);

    // We acquire a Client lock here to guard the construction of this session so that references to
    // this session are safe to use while the lock is held
    stdx::lock_guard<Client> lk(*opCtx->getClient());
    checkedOutSession.emplace(std::move(scopedCheckedOutSession));
}

ScopedBlockSessionCheckouts::ScopedBlockSessionCheckouts(OperationContext* opCtx) : _opCtx(opCtx) {
    SessionCatalog::get(_opCtx)->_disallowCheckoutsExceptForKilling();
}

ScopedBlockSessionCheckouts::~ScopedBlockSessionCheckouts() {
    SessionCatalog::get(_opCtx)->_allowCheckouts();
}

}  // namespace mongo