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>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions 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>1998-07-07</date>
    <rev>A</rev>
    <file>registry.xml</file>
  </header>
  <lib>registry</lib>
  <libsummary>Store and back up 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
      <seealso marker="mnesia:mnesia">Mnesia</seealso>
      in an atomic manner, and later restoring the contents of a
      registry from <c>Mnesia</c>.</p>
  </description>

  <funcs>
    <func>
      <name since=""><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>ei_reg_open()</c> is closed, and all the objects it
          contains are freed.</p>
        <p><c>reg</c> is the registry to close.</p>
        <p>Returns <c>0</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Deletes an object from the registry. The object is not
          removed from the registry, it is only marked for later
          removal so that on later backups to <c>Mnesia</c>, the
          corresponding object can be removed from the <c>Mnesia</c> table as
          well. If another object is later created with the same key, the
          object will be reused. </p>
        <p>The object is removed from the registry after a call to
          <c>ei_reg_dump()</c> or <c>ei_reg_purge()</c>.
        </p>
        <list type="bulleted">
          <item><c>reg</c> is the registry containing
            <c>key</c>.</item>
          <item><c>key</c> is the object to remove.</item>
        </list>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Dumps the contents of a registry to a <c>Mnesia</c> table in an
          atomic manner, that is, either all data or no data is updated.
          If any errors are encountered while backing up
          the data, the entire operation is aborted.</p>
        <list type="bulleted">
          <item><c>fd</c> is an open connection to Erlang.
            <c>Mnesia</c> 3.0 or later must be running on the Erlang node.
          </item>
          <item><c>reg</c> is the registry to back up.</item>
          <item><c>mntab</c> is the name of the <c>Mnesia</c> table
            where the backed up data is to be placed. If the table does not
            exist, it is created automatically using configurable defaults.
            For information about configuring this behavior, see
            <seealso marker="mnesia:mnesia"><c>Mnesia</c></seealso>.</item>
        </list>
        <p>If <c>flags</c> is <c>0</c>, the backup includes only
          those objects that have been created, modified, or deleted since the
          last backup or restore (that is, 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 <c>EI_FORCE</c> causes a full
          backup to be done, and <c>EI_NOPURGE</c> causes the deleted objects
          to be left in the registry afterwards. These can be bitwise OR'ed
          together if both behaviors are desired. If <c>EI_NOPURGE</c> was
          specified, <c>ei_reg_purge()</c> can be used to
          explicitly remove the deleted items from the registry later.</p>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Gets the value associated with <c>key</c> in the
          registry. The value must be a floating point type.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object will be
            looked up.</item>
          <item><c>key</c> is the name of the object to look up.
          </item>
        </list>
        <p>On success, the function returns the value associated with
          <c>key</c>.
          If the object is not found or if it is not a floating point
          object, <c>-1.0</c> is returned. To avoid problems with in-band error
          reporting (that is, if you cannot distinguish between <c>-1.0</c> and
          a valid result), use the more general function
          <c>ei_reg_getval()</c> instead.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Gets the value associated with <c>key</c> in the
          registry. The value must be an integer.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object will be
            looked up.</item>
          <item><c>key</c> is the name of the object to look up.
          </item>
        </list>
        <p>On success, the function returns the value associated with
          <c>key</c>.
          If the object is not found or if it is not an integer
          object, <c>-1</c> is returned. To avoid problems with in-band error
          reporting (that is, if you cannot distinguish between <c>-1</c> and a
          valid result), use the more general function
          <c>ei_reg_getval()</c> instead.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Gets the value associated with <c>key</c> in the
          registry. The value must be a binary (pointer) type.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object will be
            looked up.</item>
          <item><c>key</c> is the name of the object to look up.
          </item>
          <item><c>size</c> is initialized to contain the length in
            bytes of the object, if it is found.</item>
        </list>
        <p>On success, the function returns the value associated with
          <c>key</c> and indicates its length in
          <c>size</c>.
          If the object is not found or if it is not a binary object,
          <c>NULL</c> is returned. To avoid problems with in-band error
          reporting (that is, if you cannot distinguish between <c>NULL</c> and
          a valid result), use the more general function
          <c>ei_reg_getval()</c> instead.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Gets the value associated with <c>key</c> in the
          registry. The value must be a string.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object will be
            looked up.</item>
          <item><c>key</c> is the name of the object to look up.
          </item>
        </list>
        <p>On success, the function returns the value associated with
          <c>key</c>. If the object is not found or if it is not a
          string, <c>NULL</c> is returned. To avoid problems with in-band error
          reporting (that is, if you cannot distinguish between <c>NULL</c> and
          a valid result), use the more general function
          <c>ei_reg_getval()</c> instead.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>A general function for retrieving any kind of
          object from the registry.</p>
        <list type="bulleted">
          <item>
            <p><c>reg</c> is the registry where the object will be
              looked up.</p>
          </item>
          <item>
            <p><c>key</c> is the name of the object to look up.</p>
          </item>
          <item>
            <p><c>flags</c> indicates the type of object that you
              are looking for. If <c>flags</c> is <c>0</c>, any
              kind of object is returned.
              If <c>flags</c> is <c>EI_INT</c>, <c>EI_FLT</c>,
              <c>EI_STR</c>, or <c>EI_BIN</c>, then only values of
              that kind are returned.</p>
            <p>The buffer pointed to by <c>v</c>
              must be large enough to hold the return data, that is, it must be
              a pointer to one of <c>int</c>,
              <c>double</c>, <c>char*</c>, or
              <c>void*</c>, respectively.</p>
            <p>If <c>flags</c> is <c>EI_BIN</c>, a fifth argument
              <c>int *size</c> is required, so that the size of the
              object can be returned.</p>
          </item>
        </list>
        <p>On success, <c>v</c> (and <c>size</c> if the
          object is binary) is initialized with the value associated
          with <c>key</c>, and the function returns <c>EI_INT</c>,
          <c>EI_FLT</c>, <c>EI_STR</c>, or <c>EI_BIN</c>, indicating the type
          of object. On failure, <c>-1</c> is returned and the
          arguments are not updated.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Marks a registry object as dirty. This ensures that
          it is included in the next backup to <c>Mnesia</c>. Normally this
          operation is not necessary, as 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 is
          invisible to the registry and the object is assumed to be
          unmodified. This function allows you to make such modifications
          and then let the registry know about them.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry containing the object.
          </item>
          <item><c>key</c> is the name of the object to mark.
          </item>
        </list>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Opens (creates) a registry, which initially is empty. To
          close the registry later, use <c>ei_reg_close()</c>.</p>
        <p><c>size</c> is the approximate number of objects you
          intend to store in the registry. As the registry uses a hash table
          with collision chaining, no absolute upper limit exists 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. To change the size later, use
          <c>ei_reg_resize()</c>. Notice that the number
          you provide is increased to the nearest larger prime number.</p>
        <p>Returns an empty registry on success, otherwise <c>NULL</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><ret>int</ret><nametext>ei_reg_purge(reg)</nametext></name>
      <fsummary>Remove deleted objects.</fsummary>
      <type>
        <v>ei_reg *reg;</v>
      </type>
      <desc>
        <p>Removes all objects marked for deletion. When objects
          are deleted with <c>ei_reg_delete()</c> they are not
          removed from the registry, only marked for later removal.
          On a later backup to <c>Mnesia</c>, the
          objects can also be removed from the <c>Mnesia</c> table. If you are
          not backing up to <c>Mnesia</c>, you may wish to remove the objects
          manually with this function.</p>
        <p><c>reg</c> is a registry containing objects marked for
          deletion.</p>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Changes the size of a registry.</p>
        <p><c>newsize</c> is the new size to make the registry. The
          number is increased to the nearest larger prime number.</p>
        <p>On success, the registry is resized, all contents
          rehashed, and <c>0</c> is returned. On failure, the
          registry is left unchanged and <c>-1</c> is returned.</p>
      </desc>
    </func>

    <func>
      <name since=""><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 <c>Mnesia</c> table are read into the registry.</p>
        <list type="bulleted">
          <item><c>fd</c> is an open connection to Erlang.
            <c>Mnesia</c> 3.0 or later must be running on the Erlang node.
          </item>
          <item><c>reg</c> is the registry where the data is to be
            placed.</item>
          <item><c>mntab</c> is the name of the <c>Mnesia</c> table
            to read data from.</item>
        </list>
        <p>Notice that only tables of a certain format can be
          restored, that is, those that have been created and backed up to
          with <c>ei_reg_dump()</c>. If the registry was not empty
          before the operation, 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
          are overwritten with the new values. If the registry
          contains objects that were not in the table, they are
          unchanged by this operation.</p>
        <p>After the restore operation, the entire contents of the
          registry is marked as unmodified. Notice that this includes any
          objects that were modified before the restore and not
          overwritten by the restore.</p>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Creates a key-value pair with the specified <c>key</c>
          and floating point value <c>f</c>. If an object already
          exists with the same <c>key</c>, the new value replaces
          the old one. If the previous value was a binary or string, it is
          freed with <c>free()</c>.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object is to be
            placed.</item>
          <item><c>key</c> is the object name.</item>
          <item><c>f</c> is the floating point value to assign.
          </item>
        </list>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Creates a key-value pair with the specified <c>key</c>
          and integer value <c>i</c>. If an object already exists
          with the same <c>key</c>, the new value replaces the old
          one. If the previous value was a binary or string, it is freed with
          <c>free()</c>.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object is to be
            placed.</item>
          <item><c>key</c> is the object name.</item>
          <item><c>i</c> is the integer value to assign.</item>
        </list>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Creates a key-value pair with the specified <c>key</c>
          whose "value" is the binary object pointed to by <c>p</c>.
          If an object already exists with the same <c>key</c>,
          the new value replaces the old one. If the previous value was a
          binary or string, it is freed with <c>free()</c>.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object is to be
            placed.</item>
          <item><c>key</c> is the object name.</item>
          <item><c>p</c> is a pointer to the binary object. The
            object itself must have been created through a single call to
            <c>malloc()</c> or a similar function, so that the
            registry can later delete it if necessary by calling
            <c>free()</c>.</item>
          <item><c>size</c> is the length in bytes of the binary
            object.</item>
        </list>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Creates a key-value pair with the specified <c>key</c>
          whose "value" is the specified string <c>s</c>. If an
          object already exists with the same <c>key</c>, the new
          value replaces the old one. If the previous value was a binary or
          string, it is freed with <c>free()</c>.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry where the object is to be
            placed.</item>
          <item><c>key</c> is the object name.</item>
          <item><c>s</c> is the string to assign. The string itself
            must have been created through a single call to
            <c>malloc()</c> or similar a function,
            so that the registry can later delete it if
            necessary by calling <c>free()</c>.</item>
        </list>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Creates a key-value pair with the specified <c>key</c>
          whose value is specified by <c>v</c>. If an object already
          exists with the same <c>key</c>, the new value replaces
          the old one. If the previous value was a binary or string, it is freed
          with <c>free()</c>.</p>
        <list type="bulleted">
          <item>
            <p><c>reg</c> is the registry where the object is to be
              placed.</p>
          </item>
          <item>
            <p><c>key</c> is the object name.</p>
          </item>
          <item>
            <p><c>flags</c> indicates the type of the object
              specified by <c>v</c>. Flags must be one of
              <c>EI_INT</c>, <c>EI_FLT</c>, <c>EI_STR</c>, and <c>EI_BIN</c>,
              indicating whether
              <c>v</c> is <c>int</c>,
              <c>double</c>, <c>char*</c>, or
              <c>void*</c>.</p>
            <p>If <c>flags</c> is <c>EI_BIN</c>, a fifth argument
              <c>size</c> is required, indicating the size
              in bytes of the object pointed to by <c>v</c>.</p>
          </item>
        </list>
        <p>If you wish to store an arbitrary pointer in the registry,
          specify a <c>size</c> of <c>0</c>. In this case, the
          object itself is not transferred by an
          <c>ei_reg_dump()</c> operation, only the pointer
          value.</p>
        <p>Returns <c>0</c> on success, otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Returns information about an object.</p>
        <list type="bulleted">
          <item><c>reg</c> is the registry containing the object.
          </item>
          <item><c>key</c> is the object name.</item>
          <item><c>obuf</c> is a pointer to an
            <c>ei_reg_stat</c> structure, defined as follows:</item>
        </list>
        <code type="none"><![CDATA[
struct ei_reg_stat {
  int attr;
  int size;
};
        ]]></code>
        <p>In <c>attr</c> the attributes of the object are stored
          as the logical <em>OR</em> of its type (one of <c>EI_INT</c>,
          <c>EI_FLT</c>, <c>EI_BIN</c>, and <c>EI_STR</c>),
          whether it is marked for deletion (<c>EI_DELET</c>), and whether it
          has been modified since the last backup to <c>Mnesia</c>
          (<c>EI_DIRTY</c>).</p>
        <p>Field <c>size</c> indicates the size in bytes required
          to store <c>EI_STR</c> (including the terminating <c>0</c>) and
          <c>EI_BIN</c> objects, or <c>0</c> for <c>EI_INT</c> and
          <c>EI_FLT</c>.</p>
        <p>Returns <c>0</c> and initializes <c>obuf</c> on success,
          otherwise <c>-1</c>.</p>
      </desc>
    </func>

    <func>
      <name since=""><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>Returns 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>
        <list type="bulleted">
          <item><c>reg</c> is the registry to return information
            about.</item>
          <item><c>obuf</c> is a pointer to an
            <c>ei_reg_tabstat</c> structure, defined as follows:
          </item>
        </list>
        <code type="none"><![CDATA[
struct ei_reg_tabstat {
  int size;  
  int nelem; 
  int npos;  
  int collisions; 
};
        ]]></code>
        <p>Field <c>size</c> 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 number.</p>
        <list type="bulleted">
          <item><c>nelem</c> indicates the number of elements stored
            in the registry. It includes objects that are deleted but not
            purged.</item>
          <item><c>npos</c> indicates the number of unique positions
            that are occupied in the registry.</item>
          <item><c>collisions</c> indicates how many elements are
            sharing positions in the registry.</item>
        </list>
        <p>On success, <c>0</c> is returned and
          <c>obuf</c> is initialized to contain table statistics,
          otherwise <c>-1</c> is returned.</p>
      </desc>
    </func>
  </funcs>
</cref>