Classes and functions for performing hedged requests.
To perform hedged request you need to define RequestStrategy - a class similar to following ExampleStrategy:
class ExampleStrategy { public: /// Create request future.
/// Called at least once per hedged request. First time at the beginning /// of a hedged request and then every HedgingSettings::hedging_delay /// milliseconds if none of the previous requests are ready or /// ProcessReply returned non-nullopt result. If ProcessReply returned /// some interval of time, then additional request will be scheduled at /// this interval of time. ///
| attempt | - increasing number for each try std::optional<RequestType> Create(std::size_t attempt); |
/// ProcessReply is called when some request has finished. Method should /// evaluate request status and decide whether new attempt is required. /// If new attempt is required, then method must return delay for next /// attempt. If no other attempt is required, then method must return /// std::nullopt. It is expected that successful result will be stored /// somewhere internally and will be available with ExtractReply() /// method. std::optional<std::chrono::milliseconds> ProcessReply(RequestType&&);
std::optional<ReplyType> ExtractReply();
/// Method is called when system does not need request any more. /// For example, if one of the requests has been finished successfully, /// the system will finish all related subrequests. /// It is recommended to make this call as fast as possible in order /// not to block overall execution. For example, if you internally have /// some future, it is recommended to call TryCancel() here and wait /// for a cancellation in destructor, rather than call TryCancel() and /// immediately wait. void Finish(RequestType&&); };
Then call any of these functions:
Definition in file hedged_request.hpp.
Go to the source code of this file.
#include <chrono>#include <functional>#include <optional>#include <queue>#include <tuple>#include <type_traits>#include <userver/engine/task/cancel.hpp>#include <userver/engine/wait_any.hpp>#include <userver/utils/assert.hpp>#include <userver/utils/async.hpp>#include <userver/utils/datetime.hpp>
Include dependency graph for hedged_request.hpp: This graph shows which files directly or indirectly include this file:Classes | |
| struct | utils::hedging::HedgingSettings |
| Class define hedging settings. More... | |
| struct | utils::hedging::RequestTraits< RequestStrategy > |
| struct | utils::hedging::HedgedRequestBulkFuture< RequestStrategy > |
| Future of hedged bulk request. More... | |
| struct | utils::hedging::HedgedRequestFuture< RequestStrategy > |
| Future of hedged request. More... | |
Namespaces | |
| namespace | utils |
| Utilities. | |
Functions | |
| template<typename RequestStrategy > | |
| auto | utils::hedging::HedgeRequestsBulk (std::vector< RequestStrategy > inputs, HedgingSettings hedging_settings) |
| template<typename RequestStrategy > | |
| auto | utils::hedging::HedgeRequestsBulkAsync (std::vector< RequestStrategy > inputs, HedgingSettings settings) |
| template<typename RequestStrategy > | |
| std::optional< typename RequestTraits< RequestStrategy >::ReplyType > | utils::hedging::HedgeRequest (RequestStrategy input, HedgingSettings settings) |
| template<typename RequestStrategy > | |
| auto | utils::hedging::HedgeRequestAsync (RequestStrategy input, HedgingSettings settings) |
| std::optional< typename RequestTraits< RequestStrategy >::ReplyType > utils::hedging::HedgeRequest | ( | RequestStrategy | input, |
| HedgingSettings | settings ) |
Synchronously Perform hedged request described by RequestStrategy and return result or throw runtime_error. Exception can be thrown in case of timeout or if request was denied by strategy e.g. ProcessReply always returned std::nullopt or ExtractReply returned std::nullopt
Definition at line 450 of file hedged_request.hpp.
| auto utils::hedging::HedgeRequestAsync | ( | RequestStrategy | input, |
| HedgingSettings | settings ) |
Create future which perform hedged request described by RequestStrategy and return result or throw runtime_error. Exception can be thrown in case of timeout or if request was denied by strategy e.g. ProcessReply always returned std::nullopt or ExtractReply returned std::nullopt
Definition at line 466 of file hedged_request.hpp.
| auto utils::hedging::HedgeRequestsBulk | ( | std::vector< RequestStrategy > | inputs, |
| HedgingSettings | hedging_settings ) |
Synchronously perform bulk hedged requests described by RequestStrategy and return result of type std::vector<std::optional<ResultType>>. Result contains replies for each element in
| inputs | or std::nullopt in case either timeouts or bad replies (RequestStrategy::ProcessReply(RequestType&&) returned std::nullopt and RequestStrategy::ExtractReply() returned std::nullopt) |
timeout - need to process plan
Timeout but we don't have planed actions any more
Got reply but it's not OK and user wants to retry over some delay
No need to check. we just added one entry
Definition at line 365 of file hedged_request.hpp.
| auto utils::hedging::HedgeRequestsBulkAsync | ( | std::vector< RequestStrategy > | inputs, |
| HedgingSettings | settings ) |
Asynchronously perform bulk hedged requests described by RequestStrategy and return future which returns Result of type std::vector<std::optional<ResultType>>. Result contains replies for each element in
| inputs | or std::nullopt in case either timeouts or bad replies (RequestStrategy::ProcessReply(RequestType&&) returned std::nullopt and RequestStrategy::ExtractReply() returned std::nulopt) |
Definition at line 436 of file hedged_request.hpp.