View Source Registry (Elixir v1.15.4)
A local, decentralized and scalable key-value process storage.
It allows developers to lookup one or more processes with a given key.
If the registry has :unique keys, a key points to 0 or 1 process.
If the registry allows :duplicate keys, a single key may point to any
number of processes. In both cases, different keys could identify the
same process.
Each entry in the registry is associated to the process that has
registered the key. If the process crashes, the keys associated to that
process are automatically removed. All key comparisons in the registry
are done using the match operation (===/2).
The registry can be used for different purposes, such as name lookups (using
the :via option), storing properties, custom dispatching rules, or a pubsub
implementation. We explore some of those use cases below.
The registry may also be transparently partitioned, which provides more scalable behaviour for running registries on highly concurrent environments with thousands or millions of entries.
Using in :via
Once the registry is started with a given name using
Registry.start_link/1, it can be used to register and access named
processes using the {:via, Registry, {registry, key}} tuple:
{:ok, _} = Registry.start_link(keys: :unique, name: Registry.ViaTest)
name = {:via, Registry, {Registry.ViaTest, "agent"}}
{:ok, _} = Agent.start_link(fn -> 0 end, name: name)
Agent.get(name, & &1)
#=> 0
Agent.update(name, &(&1 + 1))
Agent.get(name, & &1)
#=> 1In the previous example, we were not interested in associating a value to the process:
Registry.lookup(Registry.ViaTest, "agent")
#=> [{self(), nil}]However, in some cases it may be desired to associate a value to the process
using the alternate {:via, Registry, {registry, key, value}} tuple:
{:ok, _} = Registry.start_link(keys: :unique, name: Registry.ViaTest)
name = {:via, Registry, {Registry.ViaTest, "agent", :hello}}
{:ok, agent_pid} = Agent.start_link(fn -> 0 end, name: name)
Registry.lookup(Registry.ViaTest, "agent")
#=> [{agent_pid, :hello}]To this point, we have been starting Registry using start_link/1.
Typically the registry is started as part of a supervision tree though:
{Registry, keys: :unique, name: Registry.ViaTest}Only registries with unique keys can be used in :via. If the name is
already taken, the case-specific start_link function (Agent.start_link/2
in the example above) will return {:error, {:already_started, current_pid}}.
Using as a dispatcher
Registry has a dispatch mechanism that allows developers to implement custom
dispatch logic triggered from the caller. For example, let's say we have a
duplicate registry started as so:
{:ok, _} = Registry.start_link(keys: :duplicate, name: Registry.DispatcherTest)By calling register/3, different processes can register under a given key
and associate any value under that key. In this case, let's register the
current process under the key "hello" and attach the {IO, :inspect} tuple
to it:
{:ok, _} = Registry.register(Registry.DispatcherTest, "hello", {IO, :inspect})Now, an entity interested in dispatching events for a given key may call
dispatch/3 passing in the key and a callback. This callback will be invoked
with a list of all the values registered under the requested key, alongside
the PID of the process that registered each value, in the form of {pid, value} tuples. In our example, value will be the {module, function} tuple
in the code above:
Registry.dispatch(Registry.DispatcherTest, "hello", fn entries ->
for {pid, {module, function}} <- entries, do: apply(module, function, [pid])
end)
# Prints #PID<...> where the PID is for the process that called register/3 above
#=> :okDispatching happens in the process that calls dispatch/3 either serially or
concurrently in case of multiple partitions (via spawned tasks). The
registered processes are not involved in dispatching unless involving them is
done explicitly (for example, by sending them a message in the callback).
Furthermore, if there is a failure when dispatching, due to a bad registration, dispatching will always fail and the registered process will not be notified. Therefore let's make sure we at least wrap and report those errors:
require Logger
Registry.dispatch(Registry.DispatcherTest, "hello", fn entries ->
for {pid, {module, function}} <- entries do
try do
apply(module, function, [pid])
catch
kind, reason ->
formatted = Exception.format(kind, reason, __STACKTRACE__)
Logger.error("Registry.dispatch/3 failed with #{formatted}")
end
end
end)
# Prints #PID<...>
#=> :okYou could also replace the whole apply system by explicitly sending
messages. That's the example we will see next.
Using as a PubSub
Registries can also be used to implement a local, non-distributed, scalable
PubSub by relying on the dispatch/3 function, similarly to the previous
section: in this case, however, we will send messages to each associated
process, instead of invoking a given module-function.
In this example, we will also set the number of partitions to the number of schedulers online, which will make the registry more performant on highly concurrent environments:
{:ok, _} =
Registry.start_link(
keys: :duplicate,
name: Registry.PubSubTest,
partitions: System.schedulers_online()
)
{:ok, _} = Registry.register(Registry.PubSubTest, "hello", [])
Registry.dispatch(Registry.PubSubTest, "hello", fn entries ->
for {pid, _} <- entries, do: send(pid, {:broadcast, "world"})
end)
#=> :okThe example above broadcasted the message {:broadcast, "world"} to all
processes registered under the "topic" (or "key" as we called it until now)
"hello".
The third argument given to register/3 is a value associated to the
current process. While in the previous section we used it when dispatching,
in this particular example we are not interested in it, so we have set it
to an empty list. You could store a more meaningful value if necessary.
Registrations
Looking up, dispatching and registering are efficient and immediate at the cost of delayed unsubscription. For example, if a process crashes, its keys are automatically removed from the registry but the change may not propagate immediately. This means certain operations may return processes that are already dead. When such may happen, it will be explicitly stated in the function documentation.
However, keep in mind those cases are typically not an issue. After all, a
process referenced by a PID may crash at any time, including between getting
the value from the registry and sending it a message. Many parts of the standard
library are designed to cope with that, such as Process.monitor/1 which will
deliver the :DOWN message immediately if the monitored process is already dead
and send/2 which acts as a no-op for dead processes.
ETS
Note that the registry uses one ETS table plus two ETS tables per partition.
Summary
Types
A pattern used to representing the output format part of a match spec
A guard to be evaluated when matching on objects in a registry
A list of guards to be evaluated when matching on objects in a registry
The type of keys allowed on registration
The type of the registry
The message that the registry sends to listeners when a process registers or unregisters.
A pattern to match on objects in a registry
The type of registry metadata keys
The type of registry metadata values
The registry identifier
A full match spec used when selecting objects in the registry
Options used for child_spec/1 and start_link/1
The type of values allowed on registration
Functions
Returns a specification to start a registry under a supervisor.
Returns the number of registered keys in a registry. It runs in constant time.
Returns the number of {pid, value} pairs under the given key in registry
that match pattern.
Works like select/2, but only returns the number of matching records.
Deletes registry metadata for the given key in registry.
Invokes the callback with all entries under key in each partition
for the given registry.
Returns the known keys for the given pid in registry in no particular order.
Finds the {pid, value} pair for the given key in registry in no particular order.
Returns {pid, value} pairs under the given key in registry that match pattern.
Reads registry metadata given on start_link/1.
Stores registry metadata.
Registers the current process under the given key in registry.
Select key, pid, and values registered using full match specs.
Starts the registry as a supervisor process.
Unregisters all entries for the given key associated to the current
process in registry.
Unregisters entries for keys matching a pattern associated to the current
process in registry.
Updates the value for key for the current process in the unique registry.
Reads the values for the given key for pid in registry.
Types
@type body() :: [term()]
A pattern used to representing the output format part of a match spec
A guard to be evaluated when matching on objects in a registry
@type guards() :: [guard()]
A list of guards to be evaluated when matching on objects in a registry
@type key() :: term()
The type of keys allowed on registration
@type keys() :: :unique | :duplicate
The type of the registry
@type listener_message() :: {:register, registry(), key(), registry_partition :: pid(), value()} | {:unregister, registry(), key(), registry_partition :: pid()}
The message that the registry sends to listeners when a process registers or unregisters.
See the :listeners option in start_link/1.
A pattern to match on objects in a registry
The type of registry metadata keys
@type meta_value() :: term()
The type of registry metadata values
@type registry() :: atom()
The registry identifier
@type spec() :: [{match_pattern(), guards(), body()}]
A full match spec used when selecting objects in the registry
@type start_option() :: {:keys, keys()} | {:name, registry()} | {:partitions, pos_integer()} | {:listeners, [atom()]} | {:meta, [{meta_key(), meta_value()}]}
Options used for child_spec/1 and start_link/1
@type value() :: term()
The type of values allowed on registration
Functions
@spec child_spec([start_option()]) :: Supervisor.child_spec()
Returns a specification to start a registry under a supervisor.
See Supervisor.
@spec count(registry()) :: non_neg_integer()
Returns the number of registered keys in a registry. It runs in constant time.
Examples
In the example below we register the current process and ask for the number of keys in the registry:
iex> Registry.start_link(keys: :unique, name: Registry.UniqueCountTest)
iex> Registry.count(Registry.UniqueCountTest)
0
iex> {:ok, _} = Registry.register(Registry.UniqueCountTest, "hello", :world)
iex> {:ok, _} = Registry.register(Registry.UniqueCountTest, "world", :world)
iex> Registry.count(Registry.UniqueCountTest)
2The same applies to duplicate registries:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateCountTest)
iex> Registry.count(Registry.DuplicateCountTest)
0
iex> {:ok, _} = Registry.register(Registry.DuplicateCountTest, "hello", :world)
iex> {:ok, _} = Registry.register(Registry.DuplicateCountTest, "hello", :world)
iex> Registry.count(Registry.DuplicateCountTest)
2@spec count_match(registry(), key(), match_pattern(), guards()) :: non_neg_integer()
Returns the number of {pid, value} pairs under the given key in registry
that match pattern.
Pattern must be an atom or a tuple that will match the structure of the
value stored in the registry. The atom :_ can be used to ignore a given
value or tuple element, while the atom :"$1" can be used to temporarily assign part
of pattern to a variable for a subsequent comparison.
Optionally, it is possible to pass a list of guard conditions for more precise matching.
Each guard is a tuple, which describes checks that should be passed by assigned part of pattern.
For example the $1 > 1 guard condition would be expressed as the {:>, :"$1", 1} tuple.
Please note that guard conditions will work only for assigned
variables like :"$1", :"$2", and so forth.
Avoid usage of special match variables :"$_" and :"$$", because it might not work as expected.
Zero will be returned if there is no match.
For unique registries, a single partition lookup is necessary. For duplicate registries, all partitions must be looked up.
Examples
In the example below we register the current process under the same key in a duplicate registry but with different values:
iex> Registry.start_link(keys: :duplicate, name: Registry.CountMatchTest)
iex> {:ok, _} = Registry.register(Registry.CountMatchTest, "hello", {1, :atom, 1})
iex> {:ok, _} = Registry.register(Registry.CountMatchTest, "hello", {2, :atom, 2})
iex> Registry.count_match(Registry.CountMatchTest, "hello", {1, :_, :_})
1
iex> Registry.count_match(Registry.CountMatchTest, "hello", {2, :_, :_})
1
iex> Registry.count_match(Registry.CountMatchTest, "hello", {:_, :atom, :_})
2
iex> Registry.count_match(Registry.CountMatchTest, "hello", {:"$1", :_, :"$1"})
2
iex> Registry.count_match(Registry.CountMatchTest, "hello", {:_, :_, :"$1"}, [{:>, :"$1", 1}])
1
iex> Registry.count_match(Registry.CountMatchTest, "hello", {:_, :"$1", :_}, [{:is_atom, :"$1"}])
2@spec count_select(registry(), spec()) :: non_neg_integer()
Works like select/2, but only returns the number of matching records.
Examples
In the example below we register the current process under different keys in a unique registry but with the same value:
iex> Registry.start_link(keys: :unique, name: Registry.CountSelectTest)
iex> {:ok, _} = Registry.register(Registry.CountSelectTest, "hello", :value)
iex> {:ok, _} = Registry.register(Registry.CountSelectTest, "world", :value)
iex> Registry.count_select(Registry.CountSelectTest, [{{:_, :_, :value}, [], [true]}])
2Deletes registry metadata for the given key in registry.
Examples
iex> Registry.start_link(keys: :unique, name: Registry.DeleteMetaTest)
iex> Registry.put_meta(Registry.DeleteMetaTest, :custom_key, "custom_value")
:ok
iex> Registry.meta(Registry.DeleteMetaTest, :custom_key)
{:ok, "custom_value"}
iex> Registry.delete_meta(Registry.DeleteMetaTest, :custom_key)
:ok
iex> Registry.meta(Registry.DeleteMetaTest, :custom_key)
:error@spec dispatch(registry(), key(), dispatcher, keyword()) :: :ok when dispatcher: (entries :: [{pid(), value()}] -> term()) | {module(), atom(), [any()]}
Invokes the callback with all entries under key in each partition
for the given registry.
The list of entries is a non-empty list of two-element tuples where
the first element is the PID and the second element is the value
associated to the PID. If there are no entries for the given key,
the callback is never invoked.
If the registry is partitioned, the callback is invoked multiple times
per partition. If the registry is partitioned and parallel: true is
given as an option, the dispatching happens in parallel. In both cases,
the callback is only invoked if there are entries for that partition.
See the module documentation for examples of using the dispatch/3
function for building custom dispatching or a pubsub system.
Returns the known keys for the given pid in registry in no particular order.
If the registry is unique, the keys are unique. Otherwise they may contain duplicates if the process was registered under the same key multiple times. The list will be empty if the process is dead or it has no keys in this registry.
Examples
Registering under a unique registry does not allow multiple entries:
iex> Registry.start_link(keys: :unique, name: Registry.UniqueKeysTest)
iex> Registry.keys(Registry.UniqueKeysTest, self())
[]
iex> {:ok, _} = Registry.register(Registry.UniqueKeysTest, "hello", :world)
iex> Registry.register(Registry.UniqueKeysTest, "hello", :later) # registry is :unique
{:error, {:already_registered, self()}}
iex> Registry.keys(Registry.UniqueKeysTest, self())
["hello"]Such is possible for duplicate registries though:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateKeysTest)
iex> Registry.keys(Registry.DuplicateKeysTest, self())
[]
iex> {:ok, _} = Registry.register(Registry.DuplicateKeysTest, "hello", :world)
iex> {:ok, _} = Registry.register(Registry.DuplicateKeysTest, "hello", :world)
iex> Registry.keys(Registry.DuplicateKeysTest, self())
["hello", "hello"]Finds the {pid, value} pair for the given key in registry in no particular order.
An empty list if there is no match.
For unique registries, a single partition lookup is necessary. For duplicate registries, all partitions must be looked up.
Examples
In the example below we register the current process and look it up both from itself and other processes:
iex> Registry.start_link(keys: :unique, name: Registry.UniqueLookupTest)
iex> Registry.lookup(Registry.UniqueLookupTest, "hello")
[]
iex> {:ok, _} = Registry.register(Registry.UniqueLookupTest, "hello", :world)
iex> Registry.lookup(Registry.UniqueLookupTest, "hello")
[{self(), :world}]
iex> Task.async(fn -> Registry.lookup(Registry.UniqueLookupTest, "hello") end) |> Task.await()
[{self(), :world}]The same applies to duplicate registries:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateLookupTest)
iex> Registry.lookup(Registry.DuplicateLookupTest, "hello")
[]
iex> {:ok, _} = Registry.register(Registry.DuplicateLookupTest, "hello", :world)
iex> Registry.lookup(Registry.DuplicateLookupTest, "hello")
[{self(), :world}]
iex> {:ok, _} = Registry.register(Registry.DuplicateLookupTest, "hello", :another)
iex> Enum.sort(Registry.lookup(Registry.DuplicateLookupTest, "hello"))
[{self(), :another}, {self(), :world}]Returns {pid, value} pairs under the given key in registry that match pattern.
Pattern must be an atom or a tuple that will match the structure of the
value stored in the registry. The atom :_ can be used to ignore a given
value or tuple element, while the atom :"$1" can be used to temporarily assign part
of pattern to a variable for a subsequent comparison.
Optionally, it is possible to pass a list of guard conditions for more precise matching.
Each guard is a tuple, which describes checks that should be passed by assigned part of pattern.
For example the $1 > 1 guard condition would be expressed as the {:>, :"$1", 1} tuple.
Please note that guard conditions will work only for assigned
variables like :"$1", :"$2", and so forth.
Avoid usage of special match variables :"$_" and :"$$", because it might not work as expected.
An empty list will be returned if there is no match.
For unique registries, a single partition lookup is necessary. For duplicate registries, all partitions must be looked up.
Examples
In the example below we register the current process under the same key in a duplicate registry but with different values:
iex> Registry.start_link(keys: :duplicate, name: Registry.MatchTest)
iex> {:ok, _} = Registry.register(Registry.MatchTest, "hello", {1, :atom, 1})
iex> {:ok, _} = Registry.register(Registry.MatchTest, "hello", {2, :atom, 2})
iex> Registry.match(Registry.MatchTest, "hello", {1, :_, :_})
[{self(), {1, :atom, 1}}]
iex> Registry.match(Registry.MatchTest, "hello", {2, :_, :_})
[{self(), {2, :atom, 2}}]
iex> Registry.match(Registry.MatchTest, "hello", {:_, :atom, :_}) |> Enum.sort()
[{self(), {1, :atom, 1}}, {self(), {2, :atom, 2}}]
iex> Registry.match(Registry.MatchTest, "hello", {:"$1", :_, :"$1"}) |> Enum.sort()
[{self(), {1, :atom, 1}}, {self(), {2, :atom, 2}}]
iex> guards = [{:>, :"$1", 1}]
iex> Registry.match(Registry.MatchTest, "hello", {:_, :_, :"$1"}, guards)
[{self(), {2, :atom, 2}}]
iex> guards = [{:is_atom, :"$1"}]
iex> Registry.match(Registry.MatchTest, "hello", {:_, :"$1", :_}, guards) |> Enum.sort()
[{self(), {1, :atom, 1}}, {self(), {2, :atom, 2}}]@spec meta(registry(), meta_key()) :: {:ok, meta_value()} | :error
Reads registry metadata given on start_link/1.
Atoms and tuples are allowed as keys.
Examples
iex> Registry.start_link(keys: :unique, name: Registry.MetaTest, meta: [custom_key: "custom_value"])
iex> Registry.meta(Registry.MetaTest, :custom_key)
{:ok, "custom_value"}
iex> Registry.meta(Registry.MetaTest, :unknown_key)
:error@spec put_meta(registry(), meta_key(), meta_value()) :: :ok
Stores registry metadata.
Atoms and tuples are allowed as keys.
Examples
iex> Registry.start_link(keys: :unique, name: Registry.PutMetaTest)
iex> Registry.put_meta(Registry.PutMetaTest, :custom_key, "custom_value")
:ok
iex> Registry.meta(Registry.PutMetaTest, :custom_key)
{:ok, "custom_value"}
iex> Registry.put_meta(Registry.PutMetaTest, {:tuple, :key}, "tuple_value")
:ok
iex> Registry.meta(Registry.PutMetaTest, {:tuple, :key})
{:ok, "tuple_value"}Registers the current process under the given key in registry.
A value to be associated with this registration must also be given. This value will be retrieved whenever dispatching or doing a key lookup.
This function returns {:ok, owner} or {:error, reason}.
The owner is the PID in the registry partition responsible for
the PID. The owner is automatically linked to the caller.
If the registry has unique keys, it will return {:ok, owner} unless
the key is already associated to a PID, in which case it returns
{:error, {:already_registered, pid}}.
If the registry has duplicate keys, multiple registrations from the current process under the same key are allowed.
If the registry has listeners specified via the :listeners option in start_link/1,
those listeners will be notified of the registration and will receive a
message of type listener_message/0.
Examples
Registering under a unique registry does not allow multiple entries:
iex> Registry.start_link(keys: :unique, name: Registry.UniqueRegisterTest)
iex> {:ok, _} = Registry.register(Registry.UniqueRegisterTest, "hello", :world)
iex> Registry.register(Registry.UniqueRegisterTest, "hello", :later)
{:error, {:already_registered, self()}}
iex> Registry.keys(Registry.UniqueRegisterTest, self())
["hello"]Such is possible for duplicate registries though:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateRegisterTest)
iex> {:ok, _} = Registry.register(Registry.DuplicateRegisterTest, "hello", :world)
iex> {:ok, _} = Registry.register(Registry.DuplicateRegisterTest, "hello", :world)
iex> Registry.keys(Registry.DuplicateRegisterTest, self())
["hello", "hello"]Select key, pid, and values registered using full match specs.
The spec consists of a list of three part tuples, in the shape of [{match_pattern, guards, body}].
The first part, the match pattern, must be a tuple that will match the structure of the
the data stored in the registry, which is {key, pid, value}. The atom :_ can be used to
ignore a given value or tuple element, while the atom :"$1" can be used to temporarily
assign part of pattern to a variable for a subsequent comparison. This can be combined
like {:"$1", :_, :_}.
The second part, the guards, is a list of conditions that allow filtering the results.
Each guard is a tuple, which describes checks that should be passed by assigned part of pattern.
For example the $1 > 1 guard condition would be expressed as the {:>, :"$1", 1} tuple.
Please note that guard conditions will work only for assigned
variables like :"$1", :"$2", and so forth.
The third part, the body, is a list of shapes of the returned entries. Like guards, you have access to
assigned variables like :"$1", which you can combine with hardcoded values to freely shape entries
Note that tuples have to be wrapped in an additional tuple. To get a result format like
%{key: key, pid: pid, value: value}, assuming you bound those variables in order in the match part,
you would provide a body like [%{key: :"$1", pid: :"$2", value: :"$3"}]. Like guards, you can use
some operations like :element to modify the output format.
Do not use special match variables :"$_" and :"$$", because they might not work as expected.
Note that for large registries with many partitions this will be costly as it builds the result by concatenating all the partitions.
Examples
This example shows how to get everything from the registry:
iex> Registry.start_link(keys: :unique, name: Registry.SelectAllTest)
iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "hello", :value)
iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "world", :value)
iex> Registry.select(Registry.SelectAllTest, [{{:"$1", :"$2", :"$3"}, [], [{{:"$1", :"$2", :"$3"}}]}])
[{"world", self(), :value}, {"hello", self(), :value}]Get all keys in the registry:
iex> Registry.start_link(keys: :unique, name: Registry.SelectAllTest)
iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "hello", :value)
iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "world", :value)
iex> Registry.select(Registry.SelectAllTest, [{{:"$1", :_, :_}, [], [:"$1"]}])
["world", "hello"]@spec start_link([start_option()]) :: {:ok, pid()} | {:error, term()}
Starts the registry as a supervisor process.
Manually it can be started as:
Registry.start_link(keys: :unique, name: MyApp.Registry)In your supervisor tree, you would write:
Supervisor.start_link([
{Registry, keys: :unique, name: MyApp.Registry}
], strategy: :one_for_one)For intensive workloads, the registry may also be partitioned (by specifying
the :partitions option). If partitioning is required then a good default is to
set the number of partitions to the number of schedulers available:
Registry.start_link(
keys: :unique,
name: MyApp.Registry,
partitions: System.schedulers_online()
)or:
Supervisor.start_link([
{Registry, keys: :unique, name: MyApp.Registry, partitions: System.schedulers_online()}
], strategy: :one_for_one)Options
The registry requires the following keys:
:keys- chooses if keys are:uniqueor:duplicate:name- the name of the registry and its tables
The following keys are optional:
:partitions- the number of partitions in the registry. Defaults to1.:listeners- a list of named processes which are notified of register and unregister events. The registered process must be monitored by the listener if the listener wants to be notified if the registered process crashes. Messages sent to listeners are of typelistener_message/0.:meta- a keyword list of metadata to be attached to the registry.
Unregisters all entries for the given key associated to the current
process in registry.
Always returns :ok and automatically unlinks the current process from
the owner if there are no more keys associated to the current process. See
also register/3 to read more about the "owner".
If the registry has listeners specified via the :listeners option in start_link/1,
those listeners will be notified of the unregistration and will receive a
message of type listener_message/0.
Examples
For unique registries:
iex> Registry.start_link(keys: :unique, name: Registry.UniqueUnregisterTest)
iex> Registry.register(Registry.UniqueUnregisterTest, "hello", :world)
iex> Registry.keys(Registry.UniqueUnregisterTest, self())
["hello"]
iex> Registry.unregister(Registry.UniqueUnregisterTest, "hello")
:ok
iex> Registry.keys(Registry.UniqueUnregisterTest, self())
[]For duplicate registries:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateUnregisterTest)
iex> Registry.register(Registry.DuplicateUnregisterTest, "hello", :world)
iex> Registry.register(Registry.DuplicateUnregisterTest, "hello", :world)
iex> Registry.keys(Registry.DuplicateUnregisterTest, self())
["hello", "hello"]
iex> Registry.unregister(Registry.DuplicateUnregisterTest, "hello")
:ok
iex> Registry.keys(Registry.DuplicateUnregisterTest, self())
[]unregister_match(registry, key, pattern, guards \\ [])
View Source (since 1.5.0)@spec unregister_match(registry(), key(), match_pattern(), guards()) :: :ok
Unregisters entries for keys matching a pattern associated to the current
process in registry.
Examples
For unique registries it can be used to conditionally unregister a key on the basis of whether or not it matches a particular value.
iex> Registry.start_link(keys: :unique, name: Registry.UniqueUnregisterMatchTest)
iex> Registry.register(Registry.UniqueUnregisterMatchTest, "hello", :world)
iex> Registry.keys(Registry.UniqueUnregisterMatchTest, self())
["hello"]
iex> Registry.unregister_match(Registry.UniqueUnregisterMatchTest, "hello", :foo)
:ok
iex> Registry.keys(Registry.UniqueUnregisterMatchTest, self())
["hello"]
iex> Registry.unregister_match(Registry.UniqueUnregisterMatchTest, "hello", :world)
:ok
iex> Registry.keys(Registry.UniqueUnregisterMatchTest, self())
[]For duplicate registries:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateUnregisterMatchTest)
iex> Registry.register(Registry.DuplicateUnregisterMatchTest, "hello", :world_a)
iex> Registry.register(Registry.DuplicateUnregisterMatchTest, "hello", :world_b)
iex> Registry.register(Registry.DuplicateUnregisterMatchTest, "hello", :world_c)
iex> Registry.keys(Registry.DuplicateUnregisterMatchTest, self())
["hello", "hello", "hello"]
iex> Registry.unregister_match(Registry.DuplicateUnregisterMatchTest, "hello", :world_a)
:ok
iex> Registry.keys(Registry.DuplicateUnregisterMatchTest, self())
["hello", "hello"]
iex> Registry.lookup(Registry.DuplicateUnregisterMatchTest, "hello")
[{self(), :world_b}, {self(), :world_c}]@spec update_value(registry(), key(), (value() -> value())) :: {new_value :: term(), old_value :: term()} | :error
Updates the value for key for the current process in the unique registry.
Returns a {new_value, old_value} tuple or :error if there
is no such key assigned to the current process.
If a non-unique registry is given, an error is raised.
Examples
iex> Registry.start_link(keys: :unique, name: Registry.UpdateTest)
iex> {:ok, _} = Registry.register(Registry.UpdateTest, "hello", 1)
iex> Registry.lookup(Registry.UpdateTest, "hello")
[{self(), 1}]
iex> Registry.update_value(Registry.UpdateTest, "hello", &(&1 + 1))
{2, 1}
iex> Registry.lookup(Registry.UpdateTest, "hello")
[{self(), 2}]Reads the values for the given key for pid in registry.
For unique registries, it is either an empty list or a list with a single element. For duplicate registries, it is a list with zero, one, or multiple elements.
Examples
In the example below we register the current process and look it up both from itself and other processes:
iex> Registry.start_link(keys: :unique, name: Registry.UniqueLookupTest)
iex> Registry.values(Registry.UniqueLookupTest, "hello", self())
[]
iex> {:ok, _} = Registry.register(Registry.UniqueLookupTest, "hello", :world)
iex> Registry.values(Registry.UniqueLookupTest, "hello", self())
[:world]
iex> Task.async(fn -> Registry.values(Registry.UniqueLookupTest, "hello", self()) end) |> Task.await()
[]
iex> parent = self()
iex> Task.async(fn -> Registry.values(Registry.UniqueLookupTest, "hello", parent) end) |> Task.await()
[:world]The same applies to duplicate registries:
iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateLookupTest)
iex> Registry.values(Registry.DuplicateLookupTest, "hello", self())
[]
iex> {:ok, _} = Registry.register(Registry.DuplicateLookupTest, "hello", :world)
iex> Registry.values(Registry.DuplicateLookupTest, "hello", self())
[:world]
iex> {:ok, _} = Registry.register(Registry.DuplicateLookupTest, "hello", :another)
iex> Enum.sort(Registry.values(Registry.DuplicateLookupTest, "hello", self()))
[:another, :world]