# pg2

### MODULE

pg2

### MODULE SUMMARY

Distributed Named Process Groups

### DESCRIPTION

This module implements process groups. The groups in this module differ from the groups in the module `pg` in several ways. In `pg`, each message is sent to all members in the group. In this module, each message may be sent to one, some, or all 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) which are all members of the group `foobar`. There is no special functions for sending a message to the group. Instead, client functions should be written with the functions `get_members/1` and `get_local_members/1` to find out which process are members of the group. Then the message can be sent to one or more members of the group.

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

| This module is used by the `disk_log` module for managing distributed disk logs. The disk log names are used as group names, which means that some action may need to be taken to avoid name clashes.

### EXPORTS

`create(Name) -> void()`

Types:

`Name = term()`

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

`delete(Name) -> void()`

Types:

`Name = term()`

Deletes a process group.

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

Types:

`Name = term()`

This is a useful dispatch function which can be used from client functions. It returns a process on the local node, if such a process exist. Otherwise, it chooses one randomly.

`get_members(Name) -> [Pid] | {error, Reason}`

Types:

`Name = term()`

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

`get_local_members(Name) -> [Pid] | {error, Reason}`

Types:

`Name = term()`

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

`join(Name, Pid) -> ok | {error, Reason}`

Types:

`Name = term()`

Joins the process `Pid` to the group `Name`.

`leave(Name, Pid) -> ok | {error, Reason}`

Types:

`Name = term()`

Makes the process `Pid` leave the group `Name`.

`which_groups() -> [Name]`

Types:

`Name = term()`

Returns a list of all known groups.

`start()`
`start_link() -> {ok, Pid} | {error, Reason}`

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 should be started explicitly. Use configuration parameters for `kernel` for this.

### See Also

kernel(6), pg(3)

### AUTHORS

Martin Björklund - support@erlang.ericsson.se

kernel 2.11.2
Copyright © 1991-2006 Ericsson AB