pg2

Distributed named process groups.

This module implements process groups. Each message can be sent to one, some, or all group members.

A group of processes can be accessed by a common name. For example, if there is a group named foobar, there can be a set of processes (which can be located on different nodes) that are all members of the group foobar. There are no special functions for sending a message to the group. Instead, client functions are to be written with the functions get_members/1 and get_local_members/1 to determine which processes are members of the group. Then the message can be sent to one or more group members.

If a member terminates, it is automatically removed from the group.

Warning!

This module is used by module disk_log for managing distributed disk logs. The disk log names are used as group names, which means that some action can be needed to avoid name clashes.

Types

name() = any()

The name of a process group.

Functions

create(Name :: name()) -> ok

Creates a new, empty process group. The group is globally visible on all nodes. If the group exists, nothing happens.

delete(Name :: name()) -> ok

Deletes a process group.

get_closest_pid(Name) -> pid() | {error, Reason}

  • Name = name()
  • Reason = {no_process, Name} | {no_such_group, Name}

A useful dispatch function that can be used from client functions. It returns a process on the local node, if such a process exists. Otherwise, it selects one randomly.

get_local_members(Name) ->
                     [pid()] | {error, {no_such_group, Name}}

Returns all processes running on the local node in the group Name. This function is to be used from within a client function that accesses the group. It is therefore optimized for speed.

get_members(Name) -> [pid()] | {error, {no_such_group, Name}}

Returns all processes in the group Name. This function is to be used from within a client function that accesses the group. It is therefore optimized for speed.

join(Name, Pid :: pid()) -> ok | {error, {no_such_group, Name}}

Joins the process Pid to the group Name. A process can join a group many times and must then leave the group the same number of times.

leave(Name, Pid :: pid()) -> ok | {error, {no_such_group, Name}}

Makes the process Pid leave the group Name. If the process is not a member of the group, ok is returned.

start() -> {ok, pid()} | {error, any()}

start_link() -> {ok, pid()} | {error, any()}

Starts the pg2 server. Normally, the server does not need to be started explicitly, as it is started dynamically if it is needed. This is useful during development, but in a target system the server is to be started explicitly. Use the configuration parameters for kernel(6) for this.

which_groups() -> [Name :: name()]

Returns a list of all known groups.

See Also

kernel(6)