NAME

       pg2 - 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 are 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 processes 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.

   Warning:
       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.

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}

              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, {no_such_group, Name}}

              Types:

                 Name = name()

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

       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
              should  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 several  times;
              it 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.

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

              Returns a list of all known groups.

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

SEE ALSO

       kernel(7), pg(3erl)