userver: storages::postgres::DistLockComponentBase Class Reference
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storages::postgres::DistLockComponentBase Class Referenceabstract

#include <userver/storages/postgres/dist_lock_component_base.hpp>

Detailed Description

Base class for postgres-based distlock worker components.

A component that implements a distlock with lock in Postgres. Inherit from DistLockComponentBase and implement DoWork(). Lock options are configured in static config.

The class must be used for infinite loop jobs. If you want a distributed periodic, you should look at locked_periodiccomponents::PgLockedPeriodic.

See also
dist_lock::DistLockedTask
locked_periodiccomponents::PgLockedPeriodic

Static configuration example:

example-distlock:
cluster: postgresql-service
table: service.distlocks
lockname: master
pg-timeout: 1s
lock-ttl: 10s
autostart: true

Static options:

name Description Default value
cluster postgres cluster name
table table name to store distlocks
lockname name of the lock
lock-ttl TTL of the lock; must be at least as long as the duration between subsequent cancellation checks, otherwise brain split is possible
pg-timeout timeout, must be less than lock-ttl/2
restart-delay how much time to wait after failed task restart 100ms
autostart if true, start automatically after component load false
task-processor the name of the TaskProcessor for running DoWork main-task-processor
testsuite-support Enable testsuite support false

Migration example

You have to create a SQL table for distlocks. An example of the migration script is as following:

CREATE TABLE service.distlocks
(
key TEXT PRIMARY KEY,
owner TEXT,
expiration_time TIMESTAMPTZ
);
See also
Periodics and DistLocks

Definition at line 74 of file dist_lock_component_base.hpp.

+ Inheritance diagram for storages::postgres::DistLockComponentBase:
+ Collaboration diagram for storages::postgres::DistLockComponentBase:

Public Member Functions

 DistLockComponentBase (const components::ComponentConfig &, const components::ComponentContext &)
 
dist_lock::DistLockedWorkerGetWorker ()
 
- 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

virtual void DoWork ()=0
 
virtual void DoWorkTestsuite ()
 Override this function to provide custom testsuite handler.
 
void AutostartDistLock ()
 Must be called in ctr.
 
void StopDistLock ()
 Must be called in dtr.
 

Additional Inherited Members

- Protected Types inherited from components::ComponentBase
using LoggableComponentBase = ComponentBase
 Legacy alias, use ComponentBase instead.
 

Member Function Documentation

◆ DoWork()

virtual void storages::postgres::DistLockComponentBase::DoWork ( )
protectedpure virtual

Override this function with anything that must be done under the pg lock.

Example implementation

void MyDistLockComponent::DoWork()
{
while (!engine::ShouldCancel())
{
// Start a new trace_id
auto span = tracing::Span::MakeRootSpan("my-dist-lock");
// If Foo() or other function in DoWork() throws an exception,
// DoWork() will be restarted in `restart-delay` seconds.
Foo();
// Check for cancellation after cpu-intensive Foo().
// You must check for cancellation at least every `lock-ttl`
// seconds to have time to notice lock prolongation failure.
if (engine::ShouldCancel()) break;
Bar();
}
}
Note
DoWork must honour task cancellation and stop ASAP when it is cancelled, otherwise brain split is possible (IOW, two different users do work assuming both of them hold the lock, which is not true).

◆ DoWorkTestsuite()

virtual void storages::postgres::DistLockComponentBase::DoWorkTestsuite ( )
inlineprotectedvirtual

Override this function to provide custom testsuite handler.

Definition at line 118 of file dist_lock_component_base.hpp.


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