Kernel

Reference Manual

Version 6.5.1

Table of Contents

pg2

Module

pg2

Module Summary

Distributed named process groups.

Description

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.

Data Types

name() = any()

The name of a process group.

Exports

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}

Types

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}}

Types

Name = 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}}

Types

Name = 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}}

Types

Name = 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}}

Types

Name = 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