userver: components::CachingComponentBase< T > Class Template Reference
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components::CachingComponentBase< T > Class Template Reference

#include <userver/cache/caching_component_base.hpp>

Detailed Description

template<typename T>
class components::CachingComponentBase< T >

Base class for caching components.

Provides facilities for creating periodically updated caches. You need to override cache::CacheUpdateTrait::Update then call cache::CacheUpdateTrait::StartPeriodicUpdates after setup and cache::CacheUpdateTrait::StopPeriodicUpdates before teardown. You can also override cache::CachingComponentBase::PreAssignCheck and set has-pre-assign-check: true in the static config to enable check.

Caching components must be configured in service config (see options below) and may be reconfigured dynamically via components::DynamicConfig.

Basics of Caches provide a more detailed introduction.

Dynamic config

Static options:

Name Description Default value
update-types specifies whether incremental and/or full updates will be used see below
update-interval (required) interval between Update invocations
update-jitter max. amount of time by which update-interval may be adjusted for requests dispersal update_interval / 10
full-update-interval interval between full updates
full-update-jitter max. amount of time by which full-update-interval may be adjusted for requests dispersal full-update-interval / 10
updates-enabled if false, cache updates are disabled (except for the first one if !first-update-fail-ok) true
first-update-fail-ok whether first update failure is non-fatal false
task-processor the name of the TaskProcessor for running DoWork main-task-processor
config-settings enables dynamic reconfiguration with CacheConfigSet true
exception-interval Used instead of update-interval in case of exception update_interval
additional-cleanup-interval how often to run background RCU garbage collector 10 seconds
is-strong-period whether to include Update execution time in update-interval false
testsuite-force-periodic-update override testsuite-periodic-update-enabled in TestsuiteSupport component config
failed-updates-before-expiration the number of consecutive failed updates for data expiration
has-pre-assign-check enables the check before changing the value in the cache, by default it is the check that the new value is not empty false
alert-on-failing-to-update-times fire an alert if the cache update failed specified amount of times in a row. If zero - alerts are disabled. Value from dynamic config takes priority over static 0
dump.* Manages cache behavior after dump load -
dump.first-update-mode Behavior of update after successful load from dump. See info on modes below skip
dump.first-update-type Update type after successful load from dump (full, incremental or incremental-then-async-full) full

Update types

  • full-and-incremental: both update-interval and full-update-interval must be specified. Updates with UpdateType::kIncremental will be triggered each update-interval (adjusted by jitter) unless full-update-interval has passed and UpdateType::kFull is triggered.
  • only-full: only update-interval must be specified. UpdateType::kFull will be triggered each update-interval (adjusted by jitter).
  • only-incremental: only update-interval must be specified. UpdateType::kFull is triggered on the first update, afterwards UpdateType::kIncremental will be triggered each update-interval (adjusted by jitter).

Avoiding memory leaks

If you don't implement the deletion of objects that are deleted from the data source and don't use full updates, you may get an effective memory leak, because garbage objects will pile up in the cached data.

Calculation example:

  • size of database: 1000 objects
  • removal rate: 30 objects per minute (0.5 objects per second)

Let's say we allow 20% extra garbage objects in cache in addition to the actual objects from the database. In this case we need:

full-update-interval = (size-of-database * 20% / removal-rate) = 400s

first-update-mode modes

Mode Description
skip after successful load from dump, do nothing
required make a synchronous update of type first-update-type, stop the service on failure
best-effort make a synchronous update of type first-update-type, keep working and use data from dump on failure

testsuite-force-periodic-update

use it to enable periodic cache update for a component in testsuite environment where testsuite-periodic-update-enabled from TestsuiteSupport config is false

By default, update types are guessed based on update intervals presence. If both update-interval and full-update-interval are present, full-and-incremental types is assumed. Otherwise only-full is used.

See also
dump::Dumper for more info on persistent cache dumps and corresponding config options.
Basics of Caches. pytest_userver.client.Client.invalidate_caches() for a function to force cache update from testsuite.
Examples
samples/http_caching/http_caching.cpp.

Definition at line 125 of file caching_component_base.hpp.

+ Inheritance diagram for components::CachingComponentBase< T >:
+ Collaboration diagram for components::CachingComponentBase< T >:

Public Types

using DataType = T
 

Public Member Functions

 CachingComponentBase (const ComponentConfig &config, const ComponentContext &)
 
utils::SharedReadablePtr< T > Get () const
 
utils::SharedReadablePtr< T > GetUnsafe () const
 
template<class Class >
concurrent::AsyncEventSubscriberScope UpdateAndListen (Class *obj, std::string name, void(Class::*func)(const std::shared_ptr< const T > &))
 
concurrent::AsyncEventChannel< const std::shared_ptr< const T > & > & GetEventChannel ()
 
- Public Member Functions inherited from components::ComponentBase
 ComponentBase (const ComponentConfig &, const ComponentContext &)
 
 ComponentBase (ComponentBase &&)=delete
 
 ComponentBase (const ComponentBase &)=delete
 
 ~ComponentBase () override=default
 
ComponentHealth GetComponentHealth () const override
 
void OnLoadingCancelled () override
 
void OnAllComponentsLoaded () override
 
void OnAllComponentsAreStopping () override
 
- Public Member Functions inherited from components::RawComponentBase
 RawComponentBase (RawComponentBase &&)=delete
 
 RawComponentBase (const RawComponentBase &)=delete
 

Static Public Member Functions

static yaml_config::Schema GetStaticConfigSchema ()
 
- Static Public Member Functions inherited from components::ComponentBase
static yaml_config::Schema GetStaticConfigSchema ()
 
- Static Public Member Functions inherited from components::RawComponentBase
static yaml_config::Schema GetStaticConfigSchema ()
 

Protected Member Functions

void Set (std::unique_ptr< const T > value_ptr)
 
void Set (T &&value)
 This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
 
template<typename... Args>
void Emplace (Args &&... args)
 
void Clear ()
 Clears the content of the cache by string a default constructed T.
 
virtual bool MayReturnNull () const
 
virtual void PreAssignCheck (const T *old_value_ptr, const T *new_value_ptr) const
 If the option has-pre-assign-check is set true in static config, this function is called before assigning the new value to the cache.
 
virtual void WriteContents (dump::Writer &writer, const T &contents) const
 
virtual std::unique_ptr< const T > ReadContents (dump::Reader &reader) const
 
- Protected Member Functions inherited from cache::CacheUpdateTrait
AllowedUpdateTypes GetAllowedUpdateTypes () const
 Update types configured for the cache.
 
void StartPeriodicUpdates (utils::Flags< Flag > flags={})
 Starts periodic updates.
 
void StopPeriodicUpdates ()
 Stops periodic updates.
 
void AssertPeriodicUpdateStarted ()
 
void OnCacheModified ()
 
virtual void Update (UpdateType type, const std::chrono::system_clock::time_point &last_update, const std::chrono::system_clock::time_point &now, UpdateStatisticsScope &stats_scope)=0
 Should be overridden in a derived class to align the stored data with some data source.
 
 CacheUpdateTrait (CacheUpdateTrait &&)=delete
 
CacheUpdateTraitoperator= (CacheUpdateTrait &&)=delete
 
void InvalidateAsync (UpdateType update_type)
 Non-blocking forced cache update of specified type.
 
void UpdateSyncDebug (UpdateType update_type)
 Forces a cache update of specified type.
 
const std::string & Name () const
 

Additional Inherited Members

- Protected Types inherited from components::ComponentBase
using LoggableComponentBase = ComponentBase
 Legacy alias, use ComponentBase instead.
 
- Protected Types inherited from cache::CacheUpdateTrait
enum class  Flag {
  kNone = 0 ,
  kNoFirstUpdate = 1 << 0
}
 Periodic update flags. More...
 

Member Typedef Documentation

◆ DataType

template<typename T >
using components::CachingComponentBase< T >::DataType = T

Definition at line 133 of file caching_component_base.hpp.

Constructor & Destructor Documentation

◆ CachingComponentBase()

template<typename T >
components::CachingComponentBase< T >::CachingComponentBase ( const ComponentConfig & config,
const ComponentContext & context )

Definition at line 206 of file caching_component_base.hpp.

◆ ~CachingComponentBase()

template<typename T >
components::CachingComponentBase< T >::~CachingComponentBase ( )
override

Definition at line 219 of file caching_component_base.hpp.

Member Function Documentation

◆ Clear()

template<typename T >
void components::CachingComponentBase< T >::Clear ( )
protected

Clears the content of the cache by string a default constructed T.

Definition at line 299 of file caching_component_base.hpp.

◆ Emplace()

template<typename T >
template<typename... Args>
void components::CachingComponentBase< T >::Emplace ( Args &&... args)
protected

Definition at line 294 of file caching_component_base.hpp.

◆ Get()

template<typename T >
utils::SharedReadablePtr< T > components::CachingComponentBase< T >::Get ( ) const
Returns
cache contents. May be nullptr if and only if MayReturnNull() returns true.

Definition at line 228 of file caching_component_base.hpp.

◆ GetEventChannel()

template<typename T >
concurrent::AsyncEventChannel< const std::shared_ptr< const T > & > & components::CachingComponentBase< T >::GetEventChannel ( )

Definition at line 249 of file caching_component_base.hpp.

◆ GetStaticConfigSchema()

template<typename T >
yaml_config::Schema components::CachingComponentBase< T >::GetStaticConfigSchema ( )
static

Definition at line 369 of file caching_component_base.hpp.

◆ GetUnsafe()

template<typename T >
utils::SharedReadablePtr< T > components::CachingComponentBase< T >::GetUnsafe ( ) const
Returns
cache contents. May be nullptr regardless of MayReturnNull().

Definition at line 254 of file caching_component_base.hpp.

◆ MayReturnNull()

template<typename T >
bool components::CachingComponentBase< T >::MayReturnNull ( ) const
protectedvirtual

Whether Get() is expected to return nullptr. If MayReturnNull() returns false, Get() throws an exception instead of returning nullptr.

Definition at line 304 of file caching_component_base.hpp.

◆ PreAssignCheck()

template<typename T >
void components::CachingComponentBase< T >::PreAssignCheck ( const T * old_value_ptr,
const T * new_value_ptr ) const
protectedvirtual

If the option has-pre-assign-check is set true in static config, this function is called before assigning the new value to the cache.

Note
old_value_ptr and new_value_ptr can be nullptr.

Definition at line 374 of file caching_component_base.hpp.

◆ ReadContents()

template<typename T >
std::unique_ptr< const T > components::CachingComponentBase< T >::ReadContents ( dump::Reader & reader) const
protectedvirtual

Definition at line 337 of file caching_component_base.hpp.

◆ Set() [1/2]

template<typename T >
void components::CachingComponentBase< T >::Set ( std::unique_ptr< const T > value_ptr)
protected

Sets the new value of cache. As a result the Get() member function starts returning the value passed into this function after the Update() finishes.

Warning
Do not forget to update cache::UpdateStatisticsScope, otherwise the behavior is undefined.

Definition at line 259 of file caching_component_base.hpp.

◆ Set() [2/2]

template<typename T >
void components::CachingComponentBase< T >::Set ( T && value)
protected

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Definition at line 288 of file caching_component_base.hpp.

◆ UpdateAndListen()

template<typename T >
template<typename Class >
concurrent::AsyncEventSubscriberScope components::CachingComponentBase< T >::UpdateAndListen ( Class * obj,
std::string name,
void(Class::*)(const std::shared_ptr< const T > &) func )

Subscribes to cache updates using a member function. Also immediately invokes the function with the current cache contents.

Definition at line 238 of file caching_component_base.hpp.

◆ WriteContents()

template<typename T >
void components::CachingComponentBase< T >::WriteContents ( dump::Writer & writer,
const T & contents ) const
protectedvirtual

Override to use custom serialization for cache dumps

Definition at line 327 of file caching_component_base.hpp.


The documentation for this class was generated from the following file: