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<TITLE>pool</TITLE>
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<H1>pool</H1>
</CENTER>
<H3>MODULE</H3>
<DIV CLASS=REFBODY>
pool
</DIV>
<H3>MODULE SUMMARY</H3>
<DIV CLASS=REFBODY>
Load Distribution Facility
</DIV>
<H3>DESCRIPTION</H3>
<DIV CLASS=REFBODY>
<P><CODE>pool</CODE> 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:
<P>
<UL>
<LI>
The slave nodes send regular reports to the master about
their current load.
</LI>
<LI>
Queries can be sent to the master to determine which node
will have the least load.
</LI>
</UL>
<P>The BIF <CODE>statistics(run_queue)</CODE> is used for estimating
future loads. It returns the length of the queue of ready to run
processes in the Erlang runtime system.
<P>The slave nodes are started with the <CODE>slave</CODE> module. This
effects, tty IO, file IO, and code loading.
<P>If the master node fails, the entire pool will exit.
</DIV>
<H3>EXPORTS</H3>
<P><A NAME="start/1"><STRONG><CODE>start(Name) -></CODE></STRONG></A><BR>
<A NAME="start/2"><STRONG><CODE>start(Name, Args) -> Nodes</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Name = atom()</CODE></STRONG><BR>
<STRONG><CODE>Args = string()</CODE></STRONG><BR>
<STRONG><CODE>Nodes = [node()]</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Starts a new pool. The file <CODE>.hosts.erlang</CODE> is read to
find host names where the pool nodes can be started. See
section <A HREF="#files">Files</A> below. The
start-up procedure fails if the file is not found.
<P>The slave nodes are started with <CODE>slave:start/2,3</CODE>,
passing along <CODE>Name</CODE> and, if provided, <CODE>Args</CODE>.
<CODE>Name</CODE> is used as the first part of the node names,
<CODE>Args</CODE> is used to specify command line arguments. See
<A HREF="slave.html#start/2">slave(3)</A>.
<P>Access rights must be set so that all nodes in the pool have
the authority to access each other.
<P>The function is synchronous and all the nodes, as well as
all the system servers, are running when it returns a value.
</DIV>
<P><A NAME="attach/1"><STRONG><CODE>attach(Node) -> allready_attached | attached</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Node = node()</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>This function ensures that a pool master is running and
includes <CODE>Node</CODE> in the pool master's pool of nodes.
</DIV>
<P><A NAME="stop/0"><STRONG><CODE>stop() -> stopped</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY>
<P>Stops the pool and kills all the slave nodes.
</DIV>
<P><A NAME="get_nodes/0"><STRONG><CODE>get_nodes() -> Nodes</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Nodes = [node()]</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Returns a list of the current member nodes of the pool.
</DIV>
<P><A NAME="pspawn/3"><STRONG><CODE>pspawn(Mod, Fun, Args) -> pid()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Mod = Fun = atom()</CODE></STRONG><BR>
<STRONG><CODE>Args = [term()]</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Spawns a process on the pool node which is expected to have
the lowest future load.
</DIV>
<P><A NAME="pspawn_link/3"><STRONG><CODE>pspawn_link(Mod, Fun, Args) -> pid()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY><P>Types:
<DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Mod = Fun = atom()</CODE></STRONG><BR>
<STRONG><CODE>Args = [term()]</CODE></STRONG><BR>
</DIV>
</DIV>
<DIV CLASS=REFBODY>
<P>Spawn links a process on the pool node which is expected to
have the lowest future load.
</DIV>
<P><A NAME="get_node/0"><STRONG><CODE>get_node() -> node()</CODE></STRONG></A><BR>
<DIV CLASS=REFBODY>
<P>Returns the node with the expected lowest future load.
</DIV>
<A NAME="files"><!-- Empty --></A>
<H3>Files</H3>
<DIV CLASS=REFBODY>
<P><CODE>.hosts.erlang</CODE> is used to pick hosts where nodes can
be started. See
<A HREF="javascript:erlhref('../../../../', 'kernel', 'net_adm.html#host_file/0');">net_adm(3)</A>
for information about format and location of this file.
<P><CODE>$HOME/.erlang.slave.out.HOST</CODE> is used for all additional IO
that may come from the slave nodes on standard IO. If the start-up
procedure does not work, this file may indicate the reason.
</DIV>
<H3>AUTHORS</H3>
<DIV CLASS=REFBODY>
Claes Wikstrom - support@erlang.ericsson.se<BR>
</DIV>
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<HR>
<SMALL>stdlib 1.14.2<BR>
Copyright © 1991-2006
<A HREF="http://www.erlang.se">Ericsson AB</A><BR>
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