userver: storages::mongo::DistLockComponentBase Class Reference
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storages::mongo::DistLockComponentBase Class Referenceabstract

#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::DistLockedWorkerGetWorker ()
 
- 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())
{
// Use nullptr to create new trace_id/link for an iteration
tracing::Span span(tracing::Tracer::GetTracer(), "name", nullptr);
// 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: