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<?xml version="1.0" encoding="latin1" ?>
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<!DOCTYPE cref SYSTEM "cref.dtd">
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<holder>Ericsson AB, All Rights Reserved</holder>
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The contents of this file are subject to the Erlang Public License,
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Version 1.1, (the "License"); you may not use this file except in
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compliance with the License. You should have received a copy of the
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Erlang Public License along with this software. If not, it can be
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retrieved online at http://www.erlang.org/.
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Software distributed under the License is distributed on an "AS IS"
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basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
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the License for the specific language governing rights and limitations
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The Initial Developer of the Original Code is Ericsson AB.
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<title>registry</title>
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<prepared>Gordon Beaton</prepared>
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<responsible>Gordon Beaton</responsible>
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<approved>Gordon Beaton</approved>
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<checked>Gordon Beaton</checked>
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<file>registry.sgml</file>
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<libsummary>Store and backup key-value pairs</libsummary>
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<p>This module provides support for storing key-value
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pairs in a table known as a registry, backing up registries to
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Mnesia in an atomic manner, and later restoring the contents of a
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registry from Mnesia.</p>
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<name><ret>ei_reg *</ret><nametext>ei_reg_open(size)</nametext></name>
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<fsummary>Create and open a registry</fsummary>
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<p>Open (create) a registry. The registry will be
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initially empty. Use <c><![CDATA[ei_reg_close()]]></c> to close the registry
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<p><c><![CDATA[size]]></c> is the approximate number of objects you intend
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to store in the registry. Since the registry uses a hash table
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with collision chaining, there is no absolute upper limit on the
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number of objects that can be stored in it. However for reasons
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of efficiency, it is a good idea to choose a number that is
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appropriate for your needs. It is possible to use
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<c><![CDATA[ei_reg_resize()]]></c> to change the size later. Note that the
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number you provide will be increased to the nearest larger prime
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<p>On success, an empty registry will be returned. On failure, NULL
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<name><ret>int</ret><nametext>ei_reg_resize(reg,newsize)</nametext></name>
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<fsummary>Resize a registry</fsummary>
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<p>Change the size of a registry.
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<p><c><![CDATA[newsize]]></c> is the new size to make the registry. The
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number will be increased to the nearest larger prime number.
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<p>On success, the registry will be resized, all contents
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rehashed, and the function will return 0. On failure, the
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registry will be left unchanged and the function will return -1.</p>
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<name><ret>int</ret><nametext>ei_reg_close(reg)</nametext></name>
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<fsummary>Close a registry </fsummary>
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<p>A registry that has previously been created with
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<c><![CDATA[ei_reg_open()]]></c> is closed, and all the objects it contains
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<p><c><![CDATA[reg]]></c> is the registry to close.
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<p>The function returns 0.</p>
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<name><ret>int</ret><nametext>ei_reg_setival(reg,key,i)</nametext></name>
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<fsummary>Assign an integer object</fsummary>
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<v>const char *key;</v>
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<p>Create a key-value pair with the specified <c><![CDATA[key]]></c> and integer
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value <c><![CDATA[i]]></c>. If an object already existed with the same
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<c><![CDATA[key]]></c>, the new value replaces the old one. If the previous
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value was a binary or string, it is freed with <c><![CDATA[free()]]></c>.
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<p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
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<p><c><![CDATA[key]]></c> is the name of the object.
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<p><c><![CDATA[i]]></c> is the integer value to assign.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_setfval(reg,key,f)</nametext></name>
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<fsummary>Assign a floating point object</fsummary>
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<v>const char *key;</v>
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<p>Create a key-value pair with the specified <c><![CDATA[key]]></c> and
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floating point value <c><![CDATA[f]]></c>. If an object already existed with
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the same <c><![CDATA[key]]></c>, the new value replaces the old one. If the
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previous value was a binary or string, it is freed with <c><![CDATA[free()]]></c>.
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<p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
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<p><c><![CDATA[key]]></c> is the name of the object.
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<p><c><![CDATA[f]]></c> is the floating point value to assign.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_setsval(reg,key,s)</nametext></name>
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<fsummary>Assign a string object</fsummary>
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<v>const char *key;</v>
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<v>const char *s;</v>
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<p>Create a key-value pair with the specified <c><![CDATA[key]]></c> whose
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"value" is the specified string <c><![CDATA[s]]></c>. If an object already
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existed with the same <c><![CDATA[key]]></c>, the new value replaces the old
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one. If the previous value was a binary or string, it is freed
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with <c><![CDATA[free()]]></c>.
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<p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
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<p><c><![CDATA[key]]></c> is the name of the object.
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<p><c><![CDATA[s]]></c> is the string to assign. The string itself
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must have been created through a single call to <c><![CDATA[malloc()]]></c> or
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similar function, so that the registry can later delete it if
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necessary by calling <c><![CDATA[free()]]></c>.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_setpval(reg,key,p,size)</nametext></name>
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<fsummary>Assign a binary object</fsummary>
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<v>const char *key;</v>
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<v>const void *p;</v>
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<p>Create a key-value pair with the specified <c><![CDATA[key]]></c> whose
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"value" is the binary object pointed to by <c><![CDATA[p]]></c>. If an
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object already existed with the same <c><![CDATA[key]]></c>, the new value
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replaces the old one. If the previous value was a binary or
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string, it is freed with <c><![CDATA[free()]]></c>.
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<p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
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<p><c><![CDATA[key]]></c> is the name of the object.
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<p><c><![CDATA[p]]></c> is a pointer to the binary object. The object itself
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must have been created through a single call to <c><![CDATA[malloc()]]></c> or
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similar function, so that the registry can later delete it if
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necessary by calling <c><![CDATA[free()]]></c>.
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<p><c><![CDATA[size]]></c> is the length in bytes of the binary object.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_setval(reg,key,flags,v,...)</nametext></name>
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<fsummary>Assign a value to any object type</fsummary>
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<v>const char *key;</v>
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<p>Create a key-value pair with the specified <c><![CDATA[key]]></c> whose
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value is specified by <c><![CDATA[v]]></c>. If an object already
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existed with the same <c><![CDATA[key]]></c>, the new value replaces the old
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one. If the previous value was a binary or string, it is freed
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with <c><![CDATA[free()]]></c>.
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<p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
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<p><c><![CDATA[key]]></c> is the name of the object.
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<p><c><![CDATA[flags]]></c> indicates the type of the object specified by
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<c><![CDATA[v]]></c>. Flags must be one of EI_INT, EI_FLT, EI_STR and
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EI_BIN, indicating whether <c><![CDATA[v]]></c> is <c><![CDATA[int]]></c>, <c><![CDATA[double]]></c>,
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<c><![CDATA[char*]]></c> or <c><![CDATA[void*]]></c>. If <c><![CDATA[flags]]></c> is EI_BIN, then a
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fifth argument <c><![CDATA[size]]></c> is required, indicating the size
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in bytes of the object pointed to by <c><![CDATA[v]]></c>.
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<p>If you wish to store an arbitrary pointer in the registry,
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specify a <c><![CDATA[size]]></c> of 0. In this case, the object itself will
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not be transferred by an <c><![CDATA[ei_reg_dump()]]></c> operation, just
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_getival(reg,key)</nametext></name>
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<fsummary>Get an integer object</fsummary>
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<v>const char *key;</v>
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<p>Get the value associated with <c><![CDATA[key]]></c> in the
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registry. The value must be an integer.
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<p><c><![CDATA[reg]]></c> is the registry where the object will be looked
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<p><c><![CDATA[key]]></c> is the name of the object to look up.
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<p>On success, the function returns the value associated with <c><![CDATA[key]]></c>.
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If the object was not found or it was not an integer
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object, -1 is returned. To avoid problems with in-band error
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reporting (i.e. if you cannot distinguish between -1 and a
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valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
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<name><ret>double</ret><nametext>ei_reg_getfval(reg,key)</nametext></name>
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<fsummary>Get a floating point object</fsummary>
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<v>const char *key;</v>
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<p>Get the value associated with <c><![CDATA[key]]></c> in the
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registry. The value must be a floating point type.
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<p><c><![CDATA[reg]]></c> is the registry where the object will be looked
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<p><c><![CDATA[key]]></c> is the name of the object to look up.
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<p>On success, the function returns the value associated with <c><![CDATA[key]]></c>.
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If the object was not found or it was not a floating point
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object, -1.0 is returned. To avoid problems with in-band error
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reporting (i.e. if you cannot distinguish between -1.0 and a
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valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
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<name><ret>const char *</ret><nametext>ei_reg_getsval(reg,key)</nametext></name>
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<fsummary>Get a string object</fsummary>
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<v>const char *key;</v>
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<p>Get the value associated with <c><![CDATA[key]]></c> in the
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registry. The value must be a string.
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<p><c><![CDATA[reg]]></c> is the registry where the object will be looked
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<p><c><![CDATA[key]]></c> is the name of the object to look up.
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<p>On success, the function returns the value associated with
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<c><![CDATA[key]]></c>. If the object was not found or it was not a string,
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NULL is returned. To avoid problems with in-band error
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reporting (i.e. if you cannot distinguish between NULL and a
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valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
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<name><ret>const void *</ret><nametext>ei_reg_getpval(reg,key,size)</nametext></name>
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<fsummary>Get a binary object</fsummary>
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<v>const char *key;</v>
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<p>Get the value associated with <c><![CDATA[key]]></c> in the
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registry. The value must be a binary (pointer) type.
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<p><c><![CDATA[reg]]></c> is the registry where the object will be looked
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<p><c><![CDATA[key]]></c> is the name of the object to look up.
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<p><c><![CDATA[size]]></c> will be initialized to contain the length in
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bytes of the object, if it is found.
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<p>On success, the function returns the value associated with
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<c><![CDATA[key]]></c> and indicates its length in <c><![CDATA[size]]></c>.
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If the object was not found or it was not a binary object,
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NULL is returned. To avoid problems with in-band error
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reporting (i.e. if you cannot distinguish between NULL and a
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valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
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<name><ret>int</ret><nametext>ei_reg_getval(reg,key,flags,v,...)</nametext></name>
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<fsummary>Get any object</fsummary>
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<v>const char *key;</v>
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<v>void *v (see below)</v>
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<p>This is a general function for retrieving any kind of
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object from the registry.
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<p><c><![CDATA[reg]]></c> is the registry where the object will be looked
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<p><c><![CDATA[key]]></c> is the name of the object to look up.
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<p><c><![CDATA[flags]]></c> indicates the type of object that you are
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looking for. If <c><![CDATA[flags]]></c> is 0, then any kind of object will
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be returned. If <c><![CDATA[flags]]></c> is one of EI_INT, EI_FLT, EI_STR or
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EI_BIN, then only values of that kind will be returned. The
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buffer pointed to by <c><![CDATA[v]]></c> must be large enough to hold the return
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data, i.e. it must be a pointer to one of <c><![CDATA[int]]></c>,
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<c><![CDATA[double]]></c>, <c><![CDATA[char*]]></c> or <c><![CDATA[void*]]></c>, respectively. Also,
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if <c><![CDATA[flags]]></c> is EI_BIN, then a fifth argument <c><![CDATA[int *size]]></c> is required, so that the size of the object can be
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<p>If the function succeeds, <c><![CDATA[v]]></c> (and <c><![CDATA[size]]></c> if the
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object is binary) will be initialized with the value associated
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with <c><![CDATA[key]]></c>, and the function will return one of EI_INT,
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EI_FLT, EI_STR or EI_BIN, indicating the type of object. On failure the
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function will return -1 and the arguments will not be updated.</p>
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<name><ret>int</ret><nametext>ei_reg_markdirty(reg,key)</nametext></name>
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<fsummary>Mark an object as dirty </fsummary>
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<v>const char *key;</v>
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<p>Mark a registry object as dirty. This will ensure that
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it is included in the next backup to Mnesia. Normally this
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operation will not be necessary since all of the normal registry
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'set' functions do this automatically. However if you have
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retrieved the value of a string or binary object from the
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registry and modified the contents, then the change will be
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invisible to the registry and the object will be assumed to be
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unmodified. This function allows you to make such modifications
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and then let the registry know about them.
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<p><c><![CDATA[reg]]></c> is the registry containing the object.
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<p><c><![CDATA[key]]></c> is the name of the object to mark.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_delete(reg,key)</nametext></name>
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<fsummary>Delete an object from the registry</fsummary>
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<v>const char *key;</v>
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<p>Delete an object from the registry. The object is not
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actually removed from the registry, it is only marked for later
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removal so that on subsequent backups to Mnesia, the
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corresponding object can be removed from the Mnesia table as
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well. If another object is later created with the same key, the
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object will be reused.
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<p>The object will be removed from the registry after a call to
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<c><![CDATA[ei_reg_dump()]]></c> or <c><![CDATA[ei_reg_purge()]]></c>.
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<p><c><![CDATA[reg]]></c> is the registry containing <c><![CDATA[key]]></c>.
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<p><c><![CDATA[key]]></c> is the object to remove.
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<p>If the object was found, the function returns 0 indicating
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success. Otherwise the function returns -1.</p>
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<name><ret>int</ret><nametext>ei_reg_stat(reg,key,obuf)</nametext></name>
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<fsummary>Get object information</fsummary>
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<v>const char *key;</v>
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<v>struct ei_reg_stat *obuf;</v>
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<p>Return information about an object.
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<p><c><![CDATA[reg]]></c> is the registry containing the object.
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<p><c><![CDATA[key]]></c> is the name of the object.
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<p><c><![CDATA[obuf]]></c> is a pointer to an <c><![CDATA[ei_reg_stat]]></c> structure,
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<code type="none"><![CDATA[
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<p>In <c><![CDATA[attr]]></c> the object's attributes are stored as the logical
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OR of its type (one of EI_INT, EI_FLT, EI_BIN and EI_STR),
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whether it is marked for deletion (EI_DELET) and whether it has
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been modified since the last backup to Mnesia (EI_DIRTY).
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<p>The <c><![CDATA[size]]></c> field indicates the size in bytes required to store
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EI_STR (including the terminating 0) and EI_BIN objects, or 0
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for EI_INT and EI_FLT.
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<p>The function returns 0 and initializes <c><![CDATA[obuf]]></c> on
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success, or returns -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_tabstat(reg,obuf)</nametext></name>
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<fsummary>Get registry information</fsummary>
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<v>struct ei_reg_tabstat *obuf;</v>
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<p>Return information about a registry. Using information
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returned by this function, you can see whether the size of the
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registry is suitable for the amount of data it contains.
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<p><c><![CDATA[reg]]></c> is the registry to return information about.
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<p><c><![CDATA[obuf]]></c> is a pointer to an <c><![CDATA[ei_reg_tabstat]]></c> structure,
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<code type="none"><![CDATA[
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struct ei_reg_tabstat {
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<p>The <c><![CDATA[size]]></c> field indicates the number of hash positions
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in the registry. This is the number you provided when you
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created or last resized the registry, rounded up to the nearest
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<p><c><![CDATA[nelem]]></c> indicates the number of elements stored in the
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registry. It includes objects that are deleted but not purged.
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<p><c><![CDATA[npos]]></c> indicates the number of unique positions that are
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occupied in the registry.
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<p><c><![CDATA[collisions]]></c> indicates how many elements are sharing
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positions in the registry.
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<p>On success, the function returns 0 and <c><![CDATA[obuf]]></c> is
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initialized to contain table statistics. On failure, the function
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<name><ret>int</ret><nametext>ei_reg_dump(fd,reg,mntab,flags)</nametext></name>
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<fsummary>Back up a registry to Mnesia</fsummary>
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<v>const char *mntab;</v>
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<p>Dump the contents of a registry to a Mnesia table in an
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atomic manner, i.e. either all data will be updated, or none of
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it will. If any errors are encountered while backing up
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the data, the entire operation is aborted.
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<p><c><![CDATA[fd]]></c> is an open connection to Erlang.
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Mnesia 3.0 or later must be running on the Erlang node.
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<p><c><![CDATA[reg]]></c> is the registry to back up.
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<p><c><![CDATA[mntab]]></c> is the name of the Mnesia table where the backed
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up data should be placed. If the table does not exist, it will
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be created automatically using configurable defaults. See your
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Mnesia documentation for information about configuring this
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<p>If <c><![CDATA[flags]]></c> is 0, the backup will include only those
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objects which have been created, modified or deleted since the
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last backup or restore (i.e. an incremental backup). After the
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backup, any objects that were marked dirty are now clean, and any
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objects that had been marked for deletion are deleted.
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<p>Alternatively, setting flags to EI_FORCE will cause a full
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backup to be done, and EI_NOPURGE will cause the deleted objects
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to be left in the registry afterwards. These can be bitwise ORed
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together if both behaviours are desired. If EI_NOPURGE was
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specified, you can use <c><![CDATA[ei_reg_purge()]]></c> to explicitly remove
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the deleted items from the registry later.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_restore(fd,reg,mntab)</nametext></name>
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<fsummary>Restore a registry from Mnesia</fsummary>
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<v>const char *mntab;</v>
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<p>The contents of a Mnesia table are read into the
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<p><c><![CDATA[fd]]></c> is an open connection to Erlang.
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Mnesia 3.0 or later must be running on the Erlang node.
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<p><c><![CDATA[reg]]></c> is the registry where the data should be placed.
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<p><c><![CDATA[mntab]]></c> is the name of the Mnesia table to read data
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<p>Note that only tables of a certain format can be
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restored, i.e. those that have been created and backed up to
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with <c><![CDATA[ei_reg_dump()]]></c>. If the registry was not empty before
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the operation, then the contents of the table are added to the
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contents of the registry. If the table contains objects with the
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same keys as those already in the registry, the registry objects
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will be overwritten with the new values. If the registry
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contains objects that were not in the table, they will be
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unchanged by this operation.
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<p>After the restore operation, the entire contents of the
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registry is marked as unmodified. Note that this includes any
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objects that were modified before the restore and not
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overwritten by the restore.
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<p>The function returns 0 on success, or -1 on failure.</p>
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<name><ret>int</ret><nametext>ei_reg_purge(reg)</nametext></name>
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<fsummary>Remove deleted objects</fsummary>
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<p>Remove all objects marked for deletion. When objects
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are deleted with <c><![CDATA[ei_reg_delete()]]></c> they are not actually
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removed from the registry, only marked for later removal. This
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is so that on a subsequent backup to Mnesia, the
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objects can also be removed from the Mnesia table. If you are
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not backing up to Mnesia then you may wish to remove the objects
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manually with this function.
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<p><c><![CDATA[reg]]></c> is a registry containing objects marked for
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<p>The function returns 0 on success, or -1 on failure.</p>
added
removed
lib/erl_interface/doc/src/registry.xml
