1pool(3)                    Erlang Module Definition                    pool(3)
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NAME

6       pool - Load distribution facility.
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DESCRIPTION

9       This  module can be used to run a set of Erlang nodes as a pool of com‐
10       putational processors. It is organized as a master and a set  of  slave
11       nodes and includes the following features:
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13         * The slave nodes send regular reports to the master about their cur‐
14           rent load.
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16         * Queries can be sent to the master to determine which node will have
17           the least load.
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19       The  BIF  statistics(run_queue) is used for estimating future loads. It
20       returns the length of the queue of ready to run processes in the Erlang
21       runtime system.
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23       The slave nodes are started with the slave(3) module. This effects ter‐
24       minal I/O, file I/O, and code loading.
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26       If the master node fails, the entire pool exits.
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EXPORTS

29       attach(Node) -> already_attached | attached
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31              Types:
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33                 Node = node()
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35              Ensures that a pool master is running and includes Node  in  the
36              pool master's pool of nodes.
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38       get_node() -> node()
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40              Returns the node with the expected lowest future load.
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42       get_nodes() -> [node()]
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44              Returns a list of the current member nodes of the pool.
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46       pspawn(Mod, Fun, Args) -> pid()
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48              Types:
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50                 Mod = module()
51                 Fun = atom()
52                 Args = [term()]
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54              Spawns  a  process on the pool node that is expected to have the
55              lowest future load.
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57       pspawn_link(Mod, Fun, Args) -> pid()
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59              Types:
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61                 Mod = module()
62                 Fun = atom()
63                 Args = [term()]
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65              Spawns and links to a process on the pool node that is  expected
66              to have the lowest future load.
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68       start(Name) -> Nodes
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70       start(Name, Args) -> Nodes
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72              Types:
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74                 Name = atom()
75                 Args = string()
76                 Nodes = [node()]
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78              Starts  a  new pool. The file .hosts.erlang is read to find host
79              names where the pool nodes can be started;  see  section  Files.
80              The startup procedure fails if the file is not found.
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82              The  slave nodes are started with slave:start/2,3, passing along
83              Name and, if provided, Args. Name is used as the first  part  of
84              the node names, Args is used to specify command-line arguments.
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86              Access rights must be set so that all nodes in the pool have the
87              authority to access each other.
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89              The function is synchronous and all the nodes, and all the  sys‐
90              tem servers, are running when it returns a value.
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92       stop() -> stopped
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94              Stops the pool and kills all the slave nodes.
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FILES

97       .hosts.erlang is used to pick hosts where nodes can be started. For in‐
98       formation   about   format   and   location   of   this    file,    see
99       net_adm:host_file/0.
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101       $HOME/.erlang.slave.out.HOST  is  used  for all extra I/O that can come
102       from the slave nodes on standard I/O. If the startup procedure does not
103       work, this file can indicate the reason.
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107Ericsson AB                       stdlib 4.2                           pool(3)