database_holder.h

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#pragma once

#include <set>
#include <string>

#include "mongo/base/shim.h"
#include "mongo/base/string_data.h"
#include "mongo/db/namespace_string.h"
#include "mongo/stdx/functional.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/concurrency/mutex.h"
#include "mongo/util/string_map.h"

namespace mongo {
class Database;
class OperationContext;

class DatabaseHolder {
public:
    class Impl {
    public:
        virtual ~Impl() = 0;

        virtual Database* get(OperationContext* opCtx, StringData ns) const = 0;

        virtual Database* openDb(OperationContext* opCtx, StringData ns, bool* justCreated) = 0;

        virtual void close(OperationContext* opCtx, StringData ns, const std::string& reason) = 0;

        virtual void closeAll(OperationContext* opCtx, const std::string& reason) = 0;

        virtual std::set<std::string> getNamesWithConflictingCasing(StringData name) = 0;
    };

public:
    static MONGO_DECLARE_SHIM(()->DatabaseHolder&) getDatabaseHolder;

    static MONGO_DECLARE_SHIM((PrivateTo<DatabaseHolder>)->std::unique_ptr<Impl>) makeImpl;

    inline ~DatabaseHolder() = default;

    inline explicit DatabaseHolder() : _pimpl(makeImpl(PrivateCall<DatabaseHolder>{})) {}

    inline Database* get(OperationContext* const opCtx, const StringData ns) const {
        return this->_impl().get(opCtx, ns);
    }

    inline Database* openDb(OperationContext* const opCtx,
                            const StringData ns,
                            bool* const justCreated = nullptr) {
        return this->_impl().openDb(opCtx, ns, justCreated);
    }

    inline void close(OperationContext* const opCtx,
                      const StringData ns,
                      const std::string& reason) {
        return this->_impl().close(opCtx, ns, reason);
    }

    inline void closeAll(OperationContext* const opCtx, const std::string& reason) {
        this->_impl().closeAll(opCtx, reason);
    }

    inline std::set<std::string> getNamesWithConflictingCasing(const StringData name) {
        return this->_impl().getNamesWithConflictingCasing(name);
    }

private:
    // This structure exists to give us a customization point to decide how to force users of this
    // class to depend upon the corresponding `database_holder.cpp` Translation Unit (TU).  All
    // public forwarding functions call `_impl(), and `_impl` creates an instance of this structure.
    struct TUHook {
        static void hook() noexcept;

        explicit inline TUHook() noexcept {
            if (kDebugBuild)
                this->hook();
        }
    };

    inline const Impl& _impl() const {
        TUHook{};
        return *this->_pimpl;
    }

    inline Impl& _impl() {
        TUHook{};
        return *this->_pimpl;
    }

    std::unique_ptr<Impl> _pimpl;
};
}  // namespace mongo