Load distribution facility.
This module can be used to run a set of Erlang nodes as a pool of computational processors. It is organized as a master and a set of slave nodes and includes the following features:
- The slave nodes send regular reports to the master about their current load.
- Queries can be sent to the master to determine which node will have the least load.
The BIF statistics(run_queue)
is used for estimating
future loads. It returns the length of the queue of ready to run
processes in the Erlang runtime system.
The slave nodes are started with the
slave(3)
module. This
effects terminal I/O, file I/O, and code loading.
If the master node fails, the entire pool exits.
Functions
attach(Node) -> already_attached | attached
Node = node()
Ensures that a pool master is running and includes
in the pool master's pool of nodes.
get_node() -> node()
Returns the node with the expected lowest future load.
get_nodes() -> [node()]
Returns a list of the current member nodes of the pool.
pspawn(Mod, Fun, Args) -> pid()
Mod = module()
Fun = atom()
Args = [term()]
Spawns a process on the pool node that is expected to have the lowest future load.
pspawn_link(Mod, Fun, Args) -> pid()
Mod = module()
Fun = atom()
Args = [term()]
Spawns and links to a process on the pool node that is expected to have the lowest future load.
start(Name) -> Nodes
Name = atom()
Nodes = [node()]
start(Name, Args) -> Nodes
Name = atom()
Args = string()
Nodes = [node()]
Starts a new pool. The file .hosts.erlang
is read to
find host names where the pool nodes can be started; see
section Files. The
startup procedure fails if the file is not found.
The slave nodes are started with
slave:start/2,3
,
passing along
and, if provided,
.
is used as the
first part of the node names,
is used to
specify command-line arguments.
Access rights must be set so that all nodes in the pool have the authority to access each other.
The function is synchronous and all the nodes, and all the system servers, are running when it returns a value.
stop() -> stopped
Stops the pool and kills all the slave nodes.
Files
.hosts.erlang
is used to pick hosts where nodes can
be started. For information about format and location of this file, see
net_adm:host_file/0
.
$HOME/.erlang.slave.out.HOST
is used for all extra I/O
that can come from the slave nodes on standard I/O. If the startup
procedure does not work, this file can indicate the reason.