path: root/lib/erl_interface/doc/src/registry.xml

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<!DOCTYPE cref SYSTEM "cref.dtd">

<cref>
  <header>
    <copyright>
      <year>1998</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.
    
      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.
    
    </legalnotice>

    <title>registry</title>
    <prepared>Gordon Beaton</prepared>
    <responsible>Gordon Beaton</responsible>
    <docno></docno>
    <approved>Gordon Beaton</approved>
    <checked>Gordon Beaton</checked>
    <date>980707</date>
    <rev>A</rev>
    <file>registry.sgml</file>
  </header>
  <lib>registry</lib>
  <libsummary>Store and backup key-value pairs</libsummary>
  <description>
    <p>This module provides support for storing key-value
      pairs in a table known as a registry, backing up registries to
      Mnesia in an atomic manner, and later restoring the contents of a
      registry from Mnesia.</p>
  </description>
  <funcs>
    <func>
      <name><ret>ei_reg *</ret><nametext>ei_reg_open(size)</nametext></name>
      <fsummary>Create and open a registry</fsummary>
      <type>
        <v>int size;</v>
      </type>
      <desc>
        <p>Open (create) a registry. The registry will be
          initially empty. Use <c><![CDATA[ei_reg_close()]]></c> to close the registry
          later.
          </p>
        <p><c><![CDATA[size]]></c> is the approximate number of objects you intend
          to store in the registry. Since the registry uses a hash table
          with collision chaining, there is no absolute upper limit on the
          number of objects that can be stored in it. However for reasons
          of efficiency, it is a good idea to choose a number that is
          appropriate for your needs. It is possible to use
          <c><![CDATA[ei_reg_resize()]]></c> to change the size later. Note that the
          number you provide will be increased to the nearest larger prime
          number.
          </p>
        <p>On success, an empty registry will be returned. On failure, NULL
          will be returned.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_resize(reg,newsize)</nametext></name>
      <fsummary>Resize a registry</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>int newsize;</v>
      </type>
      <desc>
        <p>Change the size of a registry.
          </p>
        <p><c><![CDATA[newsize]]></c> is the new size to make the registry. The
          number will be increased to the nearest larger prime number.
          </p>
        <p>On success, the registry will be resized, all contents
          rehashed, and the function will return 0. On failure, the
          registry will be left unchanged and the function will return -1.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_close(reg)</nametext></name>
      <fsummary>Close a registry </fsummary>
      <type>
        <v>ei_reg *reg;</v>
      </type>
      <desc>
        <p>A registry that has previously been created with
          <c><![CDATA[ei_reg_open()]]></c> is closed, and all the objects it contains
          are freed.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry to close.
          </p>
        <p>The function returns 0.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_setival(reg,key,i)</nametext></name>
      <fsummary>Assign an integer object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>int i;</v>
      </type>
      <desc>
        <p>Create a key-value pair with the specified <c><![CDATA[key]]></c> and integer
          value <c><![CDATA[i]]></c>. If an object already existed with the same
          <c><![CDATA[key]]></c>, the new value replaces the old one. If the previous
          value was a binary or string, it is freed with <c><![CDATA[free()]]></c>.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object.
          </p>
        <p><c><![CDATA[i]]></c> is the integer value to assign.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_setfval(reg,key,f)</nametext></name>
      <fsummary>Assign a floating point object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>double f;</v>
      </type>
      <desc>
        <p>Create a key-value pair with the specified <c><![CDATA[key]]></c> and
          floating point value <c><![CDATA[f]]></c>. If an object already existed with
          the same <c><![CDATA[key]]></c>, the new value replaces the old one. If the
          previous value was a binary or string, it is freed with <c><![CDATA[free()]]></c>.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object.
          </p>
        <p><c><![CDATA[f]]></c> is the floating point value to assign.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_setsval(reg,key,s)</nametext></name>
      <fsummary>Assign a string object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>const char *s;</v>
      </type>
      <desc>
        <p>Create a key-value pair with the specified <c><![CDATA[key]]></c> whose
          "value" is the specified string <c><![CDATA[s]]></c>. If an object already
          existed with the same <c><![CDATA[key]]></c>, the new value replaces the old
          one. If the previous value was a binary or string, it is freed
          with <c><![CDATA[free()]]></c>.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object.
          </p>
        <p><c><![CDATA[s]]></c> is the string to assign. The string itself
          must have been created through a single call to <c><![CDATA[malloc()]]></c> or
          similar function, so that the registry can later delete it if
          necessary by calling <c><![CDATA[free()]]></c>.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_setpval(reg,key,p,size)</nametext></name>
      <fsummary>Assign a binary object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>const void *p;</v>
        <v>int size;</v>
      </type>
      <desc>
        <p>Create a key-value pair with the specified <c><![CDATA[key]]></c> whose
          "value" is the binary object pointed to by <c><![CDATA[p]]></c>. If an
          object already existed with the same <c><![CDATA[key]]></c>, the new value
          replaces the old one. If the previous value was a binary or
          string, it is freed with <c><![CDATA[free()]]></c>.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object.
          </p>
        <p><c><![CDATA[p]]></c> is a pointer to the binary object. The object itself
          must have been created through a single call to <c><![CDATA[malloc()]]></c> or
          similar function, so that the registry can later delete it if
          necessary by calling <c><![CDATA[free()]]></c>.
          </p>
        <p><c><![CDATA[size]]></c> is the length in bytes of the binary object.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_setval(reg,key,flags,v,...)</nametext></name>
      <fsummary>Assign a value to any object type</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>int flags;</v>
        <v>v (see below)</v>
      </type>
      <desc>
        <p>Create a key-value pair with the specified <c><![CDATA[key]]></c> whose
          value is specified by <c><![CDATA[v]]></c>. If an object already
          existed with the same <c><![CDATA[key]]></c>, the new value replaces the old
          one. If the previous value was a binary or string, it is freed
          with <c><![CDATA[free()]]></c>. 
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object should be placed.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object.
          </p>
        <p><c><![CDATA[flags]]></c> indicates the type of the object specified by
          <c><![CDATA[v]]></c>. Flags must be one of EI_INT, EI_FLT, EI_STR and
          EI_BIN, indicating whether <c><![CDATA[v]]></c> is <c><![CDATA[int]]></c>, <c><![CDATA[double]]></c>,
          <c><![CDATA[char*]]></c> or <c><![CDATA[void*]]></c>. If <c><![CDATA[flags]]></c> is EI_BIN, then a
          fifth argument <c><![CDATA[size]]></c> is required, indicating the size
          in bytes of the object pointed to by <c><![CDATA[v]]></c>.
          </p>
        <p>If you wish to store an arbitrary pointer in the registry,
          specify a <c><![CDATA[size]]></c> of 0. In this case, the object itself will
          not be transferred by an <c><![CDATA[ei_reg_dump()]]></c> operation, just
          the pointer value.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_getival(reg,key)</nametext></name>
      <fsummary>Get an integer object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
      </type>
      <desc>
        <p>Get the value associated with <c><![CDATA[key]]></c> in the
          registry. The value must be an integer.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object will be looked
          up.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object to look up.
          </p>
        <p>On success, the function returns the value associated with <c><![CDATA[key]]></c>.
          If the object was not found or it was not an integer
          object, -1 is returned. To avoid problems with in-band error
          reporting (i.e. if you cannot distinguish between -1 and a
          valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
          instead.</p>
      </desc>
    </func>
    <func>
      <name><ret>double</ret><nametext>ei_reg_getfval(reg,key)</nametext></name>
      <fsummary>Get a floating point object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
      </type>
      <desc>
        <p>Get the value associated with <c><![CDATA[key]]></c> in the
          registry. The value must be a floating point type.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object will be looked
          up.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object to look up.
          </p>
        <p>On success, the function returns the value associated with <c><![CDATA[key]]></c>.
          If the object was not found or it was not a floating point
          object, -1.0 is returned. To avoid problems with in-band error
          reporting (i.e. if you cannot distinguish between -1.0 and a
          valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
          instead.</p>
      </desc>
    </func>
    <func>
      <name><ret>const char *</ret><nametext>ei_reg_getsval(reg,key)</nametext></name>
      <fsummary>Get a string object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
      </type>
      <desc>
        <p>Get the value associated with <c><![CDATA[key]]></c> in the
          registry. The value must be a string.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object will be looked
          up.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object to look up.
          </p>
        <p>On success, the function returns the value associated with
          <c><![CDATA[key]]></c>. If the object was not found or it was not a string,
          NULL is returned. To avoid problems with in-band error
          reporting (i.e. if you cannot distinguish between NULL and a
          valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
          instead.</p>
      </desc>
    </func>
    <func>
      <name><ret>const void *</ret><nametext>ei_reg_getpval(reg,key,size)</nametext></name>
      <fsummary>Get a binary object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>int size;</v>
      </type>
      <desc>
        <p>Get the value associated with <c><![CDATA[key]]></c> in the
          registry. The value must be a binary (pointer) type.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object will be looked
          up.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object to look up.
          </p>
        <p><c><![CDATA[size]]></c> will be initialized to contain the length in
          bytes of the object, if it is found.
          </p>
        <p>On success, the function returns the value associated with
          <c><![CDATA[key]]></c> and indicates its length in <c><![CDATA[size]]></c>.
          If the object was not found or it was not a binary object,
          NULL is returned. To avoid problems with in-band error
          reporting (i.e. if you cannot distinguish between NULL and a
          valid result) use the more general function <c><![CDATA[ei_reg_getval()]]></c>
          instead.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_getval(reg,key,flags,v,...)</nametext></name>
      <fsummary>Get any object</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>int flags;</v>
        <v>void *v (see below)</v>
      </type>
      <desc>
        <p>This is a general function for retrieving any kind of
          object from the registry. 
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the object will be looked
          up.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object to look up.
          </p>
        <p><c><![CDATA[flags]]></c> indicates the type of object that you are
          looking for. If <c><![CDATA[flags]]></c> is 0, then any kind of object will
          be returned. If <c><![CDATA[flags]]></c> is one of EI_INT, EI_FLT, EI_STR or
          EI_BIN, then only values of that kind will be returned. The
          buffer pointed to by <c><![CDATA[v]]></c> must be large enough to hold the return
          data, i.e. it must be a pointer to one of <c><![CDATA[int]]></c>,
          <c><![CDATA[double]]></c>, <c><![CDATA[char*]]></c> or <c><![CDATA[void*]]></c>, respectively. Also,
          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
          returned.
          </p>
        <p>If the function succeeds, <c><![CDATA[v]]></c> (and <c><![CDATA[size]]></c> if the
          object is binary) will be initialized with the value associated
          with <c><![CDATA[key]]></c>, and the function will return one of EI_INT,
          EI_FLT, EI_STR or EI_BIN, indicating the type of object. On failure the
          function will return -1 and the arguments will not be updated.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_markdirty(reg,key)</nametext></name>
      <fsummary>Mark an object as dirty </fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
      </type>
      <desc>
        <p>Mark a registry object as dirty. This will ensure that
          it is included in the next backup to Mnesia. Normally this
          operation will not be necessary since all of the normal registry
          'set' functions do this automatically. However if you have
          retrieved the value of a string or binary object from the
          registry and modified the contents, then the change will be
          invisible to the registry and the object will be assumed to be
          unmodified. This function allows you to make such modifications
          and then let the registry know about them. 
          </p>
        <p><c><![CDATA[reg]]></c> is the registry containing the object.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object to mark.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_delete(reg,key)</nametext></name>
      <fsummary>Delete an object from the registry</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
      </type>
      <desc>
        <p>Delete an object from the registry. The object is not
          actually removed from the registry, it is only marked for later
          removal so that on subsequent backups to Mnesia, the
          corresponding object can be removed from the Mnesia table as
          well. If another object is later created with the same key, the
          object will be reused. 
          </p>
        <p>The object will be removed from the registry after a call to
          <c><![CDATA[ei_reg_dump()]]></c> or <c><![CDATA[ei_reg_purge()]]></c>.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry containing <c><![CDATA[key]]></c>.
          </p>
        <p><c><![CDATA[key]]></c> is the object to remove.
          </p>
        <p>If the object was found, the function returns 0 indicating
          success. Otherwise the function returns -1.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_stat(reg,key,obuf)</nametext></name>
      <fsummary>Get object information</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>const char *key;</v>
        <v>struct ei_reg_stat *obuf;</v>
      </type>
      <desc>
        <p>Return information about an object.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry containing the object.
          </p>
        <p><c><![CDATA[key]]></c> is the name of the object.
          </p>
        <p><c><![CDATA[obuf]]></c> is a pointer to an <c><![CDATA[ei_reg_stat]]></c> structure,
          defined below:
          </p>
        <code type="none"><![CDATA[
struct ei_reg_stat {
  int attr;
  int size;
};
        ]]></code>
        <p>In <c><![CDATA[attr]]></c> the object's attributes are stored as the logical
          OR of its type (one of EI_INT, EI_FLT, EI_BIN and EI_STR),
          whether it is marked for deletion (EI_DELET) and whether it has
          been modified since the last backup to Mnesia (EI_DIRTY). 
          </p>
        <p>The <c><![CDATA[size]]></c> field indicates the size in bytes required to store
          EI_STR (including the terminating 0) and EI_BIN objects, or 0
          for EI_INT and EI_FLT.
          </p>
        <p>The function returns 0 and initializes <c><![CDATA[obuf]]></c> on
          success, or returns -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_tabstat(reg,obuf)</nametext></name>
      <fsummary>Get registry information</fsummary>
      <type>
        <v>ei_reg *reg;</v>
        <v>struct ei_reg_tabstat *obuf;</v>
      </type>
      <desc>
        <p>Return information about a registry. Using information
          returned by this function, you can see whether the size of the
          registry is suitable for the amount of data it contains.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry to return information about.
          </p>
        <p><c><![CDATA[obuf]]></c> is a pointer to an <c><![CDATA[ei_reg_tabstat]]></c> structure,
          defined below:
          </p>
        <code type="none"><![CDATA[
struct ei_reg_tabstat {
  int size;  
  int nelem; 
  int npos;  
  int collisions; 
};
        ]]></code>
        <p>The <c><![CDATA[size]]></c> field indicates the number of hash positions
          in the registry. This is the number you provided when you
          created or last resized the registry, rounded up to the nearest
          prime.
          </p>
        <p><c><![CDATA[nelem]]></c> indicates the number of elements stored in the
          registry. It includes objects that are deleted but not purged.
          </p>
        <p><c><![CDATA[npos]]></c> indicates the number of unique positions that are
          occupied in the registry. 
          </p>
        <p><c><![CDATA[collisions]]></c> indicates how many elements are sharing
          positions in the registry.
          </p>
        <p>On success, the function returns 0 and <c><![CDATA[obuf]]></c> is
          initialized to contain table statistics. On failure, the function
          returns -1.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_dump(fd,reg,mntab,flags)</nametext></name>
      <fsummary>Back up a registry to Mnesia</fsummary>
      <type>
        <v>int fd;</v>
        <v>ei_reg *reg;</v>
        <v>const char *mntab;</v>
        <v>int flags;</v>
      </type>
      <desc>
        <p>Dump the contents of a registry to a Mnesia table in an
          atomic manner, i.e. either all data will be updated, or none of
          it will. If any errors are encountered while backing up
          the data, the entire operation is aborted.
          </p>
        <p><c><![CDATA[fd]]></c> is an open connection to Erlang.
          Mnesia 3.0 or later must be running on the Erlang node.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry to back up.
          </p>
        <p><c><![CDATA[mntab]]></c> is the name of the Mnesia table where the backed
          up data should be placed. If the table does not exist, it will
          be created automatically using configurable defaults. See your
          Mnesia documentation for information about configuring this
          behaviour. 
          </p>
        <p>If <c><![CDATA[flags]]></c> is 0, the backup will include only those
          objects which have been created, modified or deleted since the
          last backup or restore (i.e. an incremental backup). After the
          backup, any objects that were marked dirty are now clean, and any
          objects that had been marked for deletion are deleted.
          </p>
        <p>Alternatively, setting flags to EI_FORCE will cause a full
          backup to be done, and EI_NOPURGE will cause the deleted objects
          to be left in the registry afterwards. These can be bitwise ORed
          together if both behaviours are desired. If EI_NOPURGE was
          specified, you can use <c><![CDATA[ei_reg_purge()]]></c> to explicitly remove
          the deleted items from the registry later. 
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_restore(fd,reg,mntab)</nametext></name>
      <fsummary>Restore a registry from Mnesia</fsummary>
      <type>
        <v>int fd;</v>
        <v>ei_reg *reg;</v>
        <v>const char *mntab;</v>
      </type>
      <desc>
        <p>The contents of a Mnesia table are read into the
          registry. 
          </p>
        <p><c><![CDATA[fd]]></c> is an open connection to Erlang.
          Mnesia 3.0 or later must be running on the Erlang node.
          </p>
        <p><c><![CDATA[reg]]></c> is the registry where the data should be placed.
          </p>
        <p><c><![CDATA[mntab]]></c> is the name of the Mnesia table to read data
          from. 
          </p>
        <p>Note that only tables of a certain format can be
          restored, i.e. those that have been created and backed up to
          with <c><![CDATA[ei_reg_dump()]]></c>. If the registry was not empty before
          the operation, then the contents of the table are added to the
          contents of the registry. If the table contains objects with the
          same keys as those already in the registry, the registry objects
          will be overwritten with the new values. If the registry
          contains objects that were not in the table, they will be
          unchanged by this operation.
          </p>
        <p>After the restore operation, the entire contents of the
          registry is marked as unmodified. Note that this includes any
          objects that were modified before the restore and not
          overwritten by the restore.  
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
    <func>
      <name><ret>int</ret><nametext>ei_reg_purge(reg)</nametext></name>
      <fsummary>Remove deleted objects</fsummary>
      <type>
        <v>ei_reg *reg;</v>
      </type>
      <desc>
        <p>Remove all objects marked for deletion. When objects
          are deleted with <c><![CDATA[ei_reg_delete()]]></c> they are not actually
          removed from the registry, only marked for later removal. This
          is so that on a subsequent backup to Mnesia, the
          objects can also be removed from the Mnesia table. If you are
          not backing up to Mnesia then you may wish to remove the objects
          manually with this function.
          </p>
        <p><c><![CDATA[reg]]></c> is a registry containing objects marked for
          deletion.
          </p>
        <p>The function returns 0 on success, or -1 on failure.</p>
      </desc>
    </func>
  </funcs>
</cref>