MediaWiki  master
docs/injection.txt File Reference

Functions

injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency 
injection (DI) refers to a pattern on object oriented programming that tries to improve modularity by reducing strong coupling between classes.In practical terms
 
Further assume MyExt::onFoo
needs service which is already
known to 
MediaWikiServices (if not, see above).*Create a non-static doFoo($x) method in MyExtHooks that has the same signature as onFoo($x).Move the code from onFoo() into doFoo()
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning 
of (MW version 1.27)
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by thereby
bootstrapping the DI framework
Per $wgServiceWiringFiles
lists includes ServiceWiring
which defines all default
service and specifies how they
depend on each 
other ("wiring").When a new service is added to MediaWiki core
 

Variables

injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by 
$wgServiceWiringFiles
 
Further assume MyExt::onFoo
needs service 
Bar
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by thereby
bootstrapping the DI framework
Per 
default
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by thereby
bootstrapping the DI framework
Per $wgServiceWiringFiles
lists includes ServiceWiring
which defines all default
service and specifies how they
depend on each an instantiator
function that will create the
appropriate default instance
for that service must be added
to ServiceWiring php This
makes the service available
through the generic getService()
method on the service locator
returned by MediaWikiServices 
Eventually
 
the only code that
instantiates Foo are
implementations of 
FooFactory
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback 
function
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency 
graph
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by thereby
bootstrapping the DI framework
Per $wgServiceWiringFiles
lists includes ServiceWiring
which defines all default
service 
implementations
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct 
instantiation
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow 
interfaces
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency 
MediaWikiServices
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of 
objects
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the 
outside
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by thereby
bootstrapping the DI framework
Per $wgServiceWiringFiles
lists includes ServiceWiring 
php
 
injection txt This is an
overview of how MediaWiki
makes use of dependency
injection The design described
here grew from the discussion
of RFC T384 The term
dependency this means that
anything an object needs to
operate should be injected
from the the object itself
should only know narrow no
concrete implementation of the
logic it relies on The
requirement to inject
everything typically results
in an architecture that based
on two main types of and
essentially stateless service
objects that use other service
objects to operate on the
value objects As of the
beginning MediaWiki is only
starting to use the DI
approach Much of the code
still relies on global state
or direct resulting in a
highly cyclical dependency
which acts as the top level
factory for services in
MediaWiki which can be used to
gain access to default
instances of various services
MediaWikiServices however also
allows new services to be
defined and default services
to be redefined Services are
defined or redefined by
providing a callback the
instantiator that will return
a new instance of the service
When it will create an
instance of MediaWikiServices
and populate it with the
services defined in the files
listed by thereby
bootstrapping the DI framework
Per $wgServiceWiringFiles
lists includes ServiceWiring
which defines all default
service and specifies how they
depend on each an instantiator
function that will create the
appropriate default instance
for that service must be added
to ServiceWiring php This
makes the service available
through the generic getService()
method on the service locator
returned by MediaWikiServices
the only code that
instantiates Foo is the
instantiator in ServiceWiring
php *As an intermediate 
step
 

Function Documentation

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency injection ( DI  )
Further assume MyExt::onFoo needs service which is already known to MediaWikiServices ( if  not,
see  above 
)
injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning of ( MW version 1.  27)
injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator that will return a new instance of the service When it will create an instance of MediaWikiServices and populate it with the services defined in the files listed by thereby bootstrapping the DI framework Per $wgServiceWiringFiles lists includes ServiceWiring which defines all default service and specifies how they depend on each other ( "wiring"  )
new

Variable Documentation

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator that will return a new instance of the service When it will create an instance of MediaWikiServices and populate it with the services defined in the files listed by $wgServiceWiringFiles

Definition at line 35 of file injection.txt.

Further assume MyExt::onFoo needs service Bar

Definition at line 214 of file injection.txt.

Referenced by SideBarTest::testTrickyPipe().

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator that will return a new instance of the service When it will create an instance of MediaWikiServices and populate it with the services defined in the files listed by thereby bootstrapping the DI framework Per default

Definition at line 35 of file injection.txt.

Eventually

Definition at line 43 of file injection.txt.

the only code that instantiates Foo are implementations of FooFactory

Definition at line 164 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator function

Definition at line 30 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency graph
Initial value:
== Overview ==
The heart of the DI in MediaWiki is the central service locator
We use the convention $dbr for read and $dbw for write to help you keep track of whether the database object is a the world will explode Or to be a subsequent write query which succeeded on the master may fail when replicated to the slave due to a unique key collision Replication on the slave will stop and it may take hours to repair the database and get it back online Setting read_only in my cnf on the slave will avoid this but given the dire we prefer to have as many checks as possible We provide a but the wrapper functions like please read the documentation for except in special pages derived from QueryPage It s a common pitfall for new developers to submit code containing SQL queries which examine huge numbers of rows Remember that COUNT * is(N), counting rows in atable is like counting beans in a bucket.------------------------------------------------------------------------Replication------------------------------------------------------------------------The largest installation of MediaWiki, Wikimedia, uses a large set ofslave MySQL servers replicating writes made to a master MySQL server.Itis important to understand the issues associated with this setup if youwant to write code destined for Wikipedia.It's often the case that the best algorithm to use for a given taskdepends on whether or not replication is in use.Due to our unabashedWikipedia-centrism, we often just use the replication-friendly version, but if you like, you can use wfGetLB() ->getServerCount() > 1 tocheck to see if replication is in use.===Lag===Lag primarily occurs when large write queries are sent to the master.Writes on the master are executed in parallel, but they are executed inserial when they are replicated to the slaves.The master writes thequery to the binlog when the transaction is committed.The slaves pollthe binlog and start executing the query as soon as it appears.They canservice reads while they are performing a write query, but will not readanything more from the binlog and thus will perform no more writes.Thismeans that if the write query runs for a long time, the slaves will lagbehind the master for the time it takes for the write query to complete.Lag can be exacerbated by high read load.MediaWiki's load balancer willstop sending reads to a slave when it is lagged by more than 30 seconds.If the load ratios are set incorrectly, or if there is too much loadgenerally, this may lead to a slave permanently hovering around 30seconds lag.If all slaves are lagged by more than 30 seconds, MediaWiki will stopwriting to the database.All edits and other write operations will berefused, with an error returned to the user.This gives the slaves achance to catch up.Before we had this mechanism, the slaves wouldregularly lag by several minutes, making review of recent editsdifficult.In addition to this, MediaWiki attempts to ensure that the user seesevents occurring on the wiki in chronological order.A few seconds of lagcan be tolerated, as long as the user sees a consistent picture fromsubsequent requests.This is done by saving the master binlog positionin the session, and then at the start of each request, waiting for theslave to catch up to that position before doing any reads from it.Ifthis wait times out, reads are allowed anyway, but the request isconsidered to be in"lagged slave mode".Lagged slave mode can bechecked by calling wfGetLB() ->getLaggedSlaveMode().The onlypractical consequence at present is a warning displayed in the pagefooter.===Lag avoidance===To avoid excessive lag, queries which write large numbers of rows shouldbe split up, generally to write one row at a time.Multi-row INSERT...SELECT queries are the worst offenders should be avoided altogether.Instead do the select first and then the insert.===Working with lag===Despite our best efforts, it's not practical to guarantee a low-lagenvironment.Lag will usually be less than one second, but mayoccasionally be up to 30 seconds.For scalability, it's very importantto keep load on the master low, so simply sending all your queries tothe master is not the answer.So when you have a genuine need forup-to-date data, the following approach is advised:1) Do a quick query to the master for a sequence number or timestamp 2) Run the full query on the slave and check if it matches the data you gotfrom the master 3) If it doesn't, run the full query on the masterTo avoid swamping the master every time the slaves lag, use of thisapproach should be kept to a minimum.In most cases you should just readfrom the slave and let the user deal with the delay.------------------------------------------------------------------------Lock contention------------------------------------------------------------------------Due to the high write rate on Wikipedia(and some other wikis), MediaWiki developers need to be very careful to structure their writesto avoid long-lasting locks.By default, MediaWiki opens a transactionat the first query, and commits it before the output is sent.Locks willbe held from the time when the query is done until the commit.So youcan reduce lock time by doing as much processing as possible before youdo your write queries.Often this approach is not good enough, and it becomes necessary toenclose small groups of queries in their own transaction.Use thefollowing syntax:$dbw=wfGetDB(DB_MASTER
null for the local wiki Added in
Definition: hooks.txt:1584
A helper class for throttling authentication attempts.
injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning of(MW version 1.27)

Definition at line 23 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator that will return a new instance of the service When it will create an instance of MediaWikiServices and populate it with the services defined in the files listed by thereby bootstrapping the DI framework Per $wgServiceWiringFiles lists includes ServiceWiring which defines all default service implementations

Definition at line 35 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct instantiation

Definition at line 20 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow interfaces

Definition at line 10 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency MediaWikiServices
injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of objects

Definition at line 10 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the outside

Definition at line 10 of file injection.txt.

injection txt This is an overview of how MediaWiki makes use of dependency injection The design described here grew from the discussion of RFC T384 The term dependency this means that anything an object needs to operate should be injected from the the object itself should only know narrow no concrete implementation of the logic it relies on The requirement to inject everything typically results in an architecture that based on two main types of and essentially stateless service objects that use other service objects to operate on the value objects As of the beginning MediaWiki is only starting to use the DI approach Much of the code still relies on global state or direct resulting in a highly cyclical dependency which acts as the top level factory for services in MediaWiki which can be used to gain access to default instances of various services MediaWikiServices however also allows new services to be defined and default services to be redefined Services are defined or redefined by providing a callback the instantiator that will return a new instance of the service When it will create an instance of MediaWikiServices and populate it with the services defined in the files listed by thereby bootstrapping the DI framework Per $wgServiceWiringFiles lists includes ServiceWiring php
the only code that instantiates Foo are implementations of and the only code that instantiates FooFactory is the instantiator in ServiceWiring php *As an intermediate step

Definition at line 43 of file injection.txt.