federated_topic.hpp

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#pragma once
 
/// @file userver/ydb/federated_topic.hpp
/// @brief YDB Federated Topic client
///
/// Federated Topic SDK serves as a wrapper over Topic SDK, coordinates
/// reading from federated YDB installations topics, has a subset of functions
/// of usual Topic SDK
///
/// @ref userver/ydb/topic.hpp
 
#include <chrono>
#include <memory>
#include <optional>
 
#include <ydb-cpp-sdk/client/federated_topic/federated_topic.h>
#include <ydb-cpp-sdk/client/types/executor/executor.h>
 
#include <userver/compiler/impl/lifetime.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace ydb {
 
namespace impl {
class Driver;
struct TopicSettings;
}  // namespace impl
 
/// @brief Read session used to connect to one or more topics for reading
///
/// @see https://ydb.tech/docs/en/reference/ydb-sdk/topic#reading
///
/// ## Example usage:
///
/// @ref samples/ydb_service/components/federated_topic_reader.hpp
/// @ref samples/ydb_service/components/federated_topic_reader.cpp
///
/// @example samples/ydb_service/components/federated_topic_reader.hpp
/// @example samples/ydb_service/components/federated_topic_reader.cpp
class FederatedTopicReadSession final {
public:
    /// @cond
    // For internal use only.
    explicit FederatedTopicReadSession(std::shared_ptr<NYdb::NFederatedTopic::IFederatedReadSession> read_session);
    /// @endcond
 
    /// @brief Get read session events
    ///
    /// Waits until event occurs
    /// @param max_events_count maximum events count in batch
    /// @param max_size_bytes total size limit for data messages in batch
    /// if not specified, read session chooses event batch size automatically
    std::vector<NYdb::NFederatedTopic::TReadSessionEvent::TEvent> GetEvents(
        std::optional<std::size_t> max_events_count = {},
        size_t max_size_bytes = std::numeric_limits<size_t>::max()
    );
 
    /// @brief Close read session
    ///
    /// Waits for all commit acknowledgments to arrive.
    /// Force close after timeout
    bool Close(std::chrono::milliseconds timeout);
 
    /// @brief Get native read session
    ///
    /// @warning Use with care! Facilities from @ref userver/drivers/subscribable_futures.hpp can help
    /// with non-blocking wait operations.
    NYdb::NFederatedTopic::IFederatedReadSession& GetNativeTopicReadSession() USERVER_IMPL_LIFETIME_BOUND;
 
private:
    std::shared_ptr<NYdb::NFederatedTopic::IFederatedReadSession> read_session_;
};
 
/// @ingroup userver_clients
///
/// @brief YDB Federated Topic Client
///
/// @see https://ydb.tech/docs/en/concepts/topic
class FederatedTopicClient final {
public:
    /// @cond
    // For internal use only.
    FederatedTopicClient(std::shared_ptr<impl::Driver> driver, impl::TopicSettings settings);
    /// @endcond
 
    ~FederatedTopicClient();
 
    /// Create read session
    FederatedTopicReadSession CreateReadSession(const NYdb::NFederatedTopic::TFederatedReadSessionSettings& settings);
 
    /// Get native topic client
    /// @warning Use with care! Facilities from
    /// `<core/include/userver/drivers/subscribable_futures.hpp>` can help with
    /// non-blocking wait operations.
    NYdb::NFederatedTopic::TFederatedTopicClient& GetNativeTopicClient() USERVER_IMPL_LIFETIME_BOUND;
 
private:
    std::shared_ptr<impl::Driver> driver_;
    // Owned executors: Stop() only after `topic_client_` is destroyed (see
    // ~FederatedTopicClient). Joining these threads after the native client is
    // gone avoids atexit use-after-destroy (e.g. SEGV in TCodecMap). Stopping
    // them while TFederatedTopicClient is still alive would deadlock or stall
    // writes.
    NYdb::IExecutor::TPtr compression_executor_;
    NYdb::IExecutor::TPtr handlers_executor_;
    // `reset()` in ~FederatedTopicClient runs before Stop() on the executors
    // above.
    std::optional<NYdb::NFederatedTopic::TFederatedTopicClient> topic_client_;
};
 
}  // namespace ydb
 
USERVER_NAMESPACE_END