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

Detailed Description

Base class for mongo-based distlock worker components.

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

Mongo might not perform well on a high load, so you might want to use postgres-based distlock storages::postgres::DistLockComponentBase instead.

See also: storages::postgres::DistLockComponentBase

Cancellation checks

Functions engine::current_task::ShouldCancel(), engine::InterruptibleSleepFor(), engine::InterruptibleSleepUntil() and engine::current_task::CancellationPoint() check for task cancellation. Overridden DistLockComponentBase::DoWork must use the above functions to honour task cancellation and stop ASAP when it is cancelled.

Static configuration example:

example-distlock:
    lockname: master
    mongo-timeout: 1s
    lock-ttl: 10s

Static options:

name	Description	Default value
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	–
mongo-timeout	timeout, must be less than lock-ttl / 2	–
restart-delay	how much time to wait after failed task restart	100ms
task-processor	the name of the TaskProcessor for running DoWork	main-task-processor
testsuite-support	Enable testsuite support	false

See also: Periodics and DistLocks

Definition at line 61 of file dist_lock_component_base.hpp.

Inheritance diagram for storages::mongo::DistLockComponentBase:

Collaboration diagram for storages::mongo::DistLockComponentBase:

Public Member Functions
	DistLockComponentBase (const components::ComponentConfig &, const components::ComponentContext &, storages::mongo::Collection)

dist_lock::DistLockedWorker &	GetWorker ()

Public Member Functions inherited from components::LoggableComponentBase
	LoggableComponentBase (const ComponentConfig &, const ComponentContext &)

	LoggableComponentBase (LoggableComponentBase &&)=delete

	LoggableComponentBase (const LoggableComponentBase &)=delete

	~LoggableComponentBase () override=default

ComponentHealth	GetComponentHealth () const override

void	OnLoadingCancelled () override

void	OnAllComponentsLoaded () override

void	OnAllComponentsAreStopping () override

Static Public Member Functions
static yaml_config::Schema	GetStaticConfigSchema ()

Static Public Member Functions inherited from components::LoggableComponentBase
static yaml_config::Schema	GetStaticConfigSchema ()

Protected Member Functions
virtual void	DoWork ()=0

virtual void	DoWorkTestsuite ()
	Override this function to provide custom testsuite handler.

void	Start ()
	Must be called in constructor.

void	Stop ()
	Must be called in destructor.

Member Function Documentation

◆ DoWork()

virtual void storages::mongo::DistLockComponentBase::DoWork ( )

protectedpure virtual

Override this function with anything that must be done under the mongo 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::mongo::DistLockComponentBase::DoWorkTestsuite ( )

inlineprotectedvirtual

Override this function to provide custom testsuite handler.

Definition at line 107 of file dist_lock_component_base.hpp.

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

userver/storages/mongo/dist_lock_component_base.hpp