<?xml version="1.0"?>
<!DOCTYPE gsdoc PUBLIC "-//GNUstep//DTD gsdoc 1.0.3//EN" "http://www.gnustep.org/gsdoc-1_0_3.dtd">
<gsdoc base="GSFIFO">
  <head>
    <title>GSFIFO class documentation</title>
    <author name="Richard Frith-Macdonald">
      <email address="rfm@gnu.org">
        rfm@gnu.org
      </email>
    </author>
    <copy>2011 Free Software Foundation, Inc.</copy>
  </head>
  <body>
    <front><contents /></front>
    <chapter>
      <heading>
        Software documentation for the GSFIFO class
      </heading>
      <class name="GSFIFO" super="NSObject">
        <declared>GSFIFO.h</declared>
        <desc>
          GSFIFO manages a first-in-first-out queue of items.
          <br /> Items in the queue are <em>NOT</em> retained
          objects... memory management is not the job of this
          class and it is not intended to be treated as a
          'collection', rather its role is intended to be
          that of an inter-thread coordination mechanism. <br />
          Instances of the GSFIFO class are intended to
          support the producer-consumer model of processing.
          The ideal example is that of a production line, where you
          have a stream of items to be processed and while that
          processing can be broken down into separate
          stages, they must be done in a particular order. The
          FIFO is used as the link betwen those stages, ensuring
          that the required ordering is maintained even when
          separate threads handle each stage. <br /> Where
          there is a single producer and a single consumer
          thread, a fast lock-free algorthm is used to get/pu
          items from the FIFO. <br /> To minimise the overheads
          of using the FIFO, we provide inline functions to support
          the addition of items in the single producer thread case
          and to support the removal of items in the single
          consumer thread case. When operating that way, the
          overhead of using the FIFO is only a few CPU cycles
          and it becomes reasonable to split sequentional
          processing into a <strong>long</strong> series of
          small operations each handled by a separate thread
          (making effective use of a multi-cpu machine). <br />
          The FIFO may also be useful where you don't have a
          strictly sequential process to manage, but some
          parts need to be sequential... in these cases it may
          make sense to have multiple consumers and/or producers.
          In these cases, some locking is required and the use of
          the inline functions is not allowed (you must call the
          <ref type="method" id="-get">
            -get
          </ref>
          and <ref type="method" id="-put:">-put:</ref> methods.
          <br /> It is recommended that you create FIFOs using
          the
          <ref type="method" id="-initWithName:">
            -initWithName:
          </ref>
          method so that you can easily use the NSUserDefaults
          system to adjust their configurations to tests/tweak
          performance.
        </desc>
        <ivariable type="uint32_t" name="_capacity" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="uint64_t" name="_getTryFailure" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="uint64_t" name="_getTrySuccess" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="volatile uint64_t" name="_head" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="void**" name="_items" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="uint64_t" name="_putTryFailure" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="uint64_t" name="_putTrySuccess" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <ivariable type="volatile uint64_t" name="_tail" validity="public">
          <desc>
            <em>Warning</em> the underscore at the start of the
            name of this instance variable indicates that, even
            though it is not technically <em>private</em>, it is
            intended for internal use within the package, and
            you should not use the variable in other code.
          </desc>
        </ivariable>
        <method type="NSString*" factory="yes">
          <sel>stats</sel>
          <desc>
            Return statistics for all current GSFIFO instances.
            <br /> Statistics for FIFOs which are configued to
            be lock-free are empty (listing the name only) except
            where we can safely obtain get or put stats because
            the FIFOs consumer/producer thread is the same as the
            current thread.
          </desc>
        </method>
        <method type="NSUInteger">
          <sel>count</sel>
          <desc>
            Returns the approximate number of items in the
            FIFO.
          </desc>
        </method>
        <method type="void*">
          <sel>get</sel>
          <desc>
            Gets the next item from the FIFO, blocking if
            necessary until an item is available. Raises an
            exception if the FIFO is configured with a
            timeout and it is exceeded. <br /> Implemented
            using
            <ref type="method" id="-get:count:shouldBlock:">
              -get:count:shouldBlock:
            </ref>
          </desc>
        </method>
        <method type="unsigned">
          <sel>get:</sel>
          <arg type="void**">buf</arg>
          <sel>count:</sel>
          <arg type="unsigned">count</arg>
          <sel>shouldBlock:</sel>
          <arg type="BOOL">block</arg>
          <desc>
            Reads up to <var>count</var> items from the FIFO into
            <var>buf</var>. If <var>block</var> is
            <code>YES</code>, this blocks if necessary until at
            least one item is available, and raises an exception
            if the FIFO is configured with a timeout and it is
            exceeded. <br /> Returns the number of items
            actually read.
          </desc>
        </method>
        <method type="id" init="yes">
          <sel>initWithCapacity:</sel>
          <arg type="uint32_t">c</arg>
          <sel>granularity:</sel>
          <arg type="uint16_t">g</arg>
          <sel>timeout:</sel>
          <arg type="uint16_t">t</arg>
          <sel>multiProducer:</sel>
          <arg type="BOOL">mp</arg>
          <sel>multiConsumer:</sel>
          <arg type="BOOL">mc</arg>
          <sel>boundaries:</sel>
          <arg type="NSArray*">a</arg>
          <sel>name:</sel>
          <arg type="NSString*">n</arg>
          <desc>
            Initialises the receiver with the specified
            capacity (buffer size). <br /> The capacity must
            lie in the range from one to <var>a</var> million,
            othewrwise the receiver is deallocated and this
            method returns <code>nil</code>. <br /> If the
            granularity value is non-zero, it is treated as
            the maximum time in milliseconds for which <var>a</var>
            <ref type="method" id="-get">
              -get
            </ref>
            or <ref type="method" id="-put:">-put:</ref> operation
            will pause between successive attempts. <br /> If the
            timeout value is non-zero, it is treated as the
            total time in milliseconds for which <var>a</var>
            <ref type="method" id="-get">
              -get
            </ref>
            or <ref type="method" id="-put:">-put:</ref> operation
            may block, and <var>a</var> longer delay will cause
            those methods to raise an exception. <br /> If the
            multiProducer or multiConsumer flag is
            <code>YES</code>, the FIFO is configured to support
            multiple producer/consumer threads using locking.
            <br /> The boundaries array is an ordered list of
            NSNumber objects containing time intervals found
            boundaries of bands into which to categorise
            wait time stats. Any wait whose duration is less than
            the interval specified in the Nth element is counted in
            the stat's for the Nth band. If this is
            <code>nil</code>, <var>a</var> default set of
            bundaries is used. If it is an empty array then
            no time based stats are recorded. <br /> The name string
            is <var>a</var> unique identifier for the receiver and
            is used when printing diagnostics and statistics. If an
            instance with the same name already exists, the
            receiveris deallocated and an exception is
            raised.
          </desc>
        </method>
        <method type="id">
          <sel>initWithCapacity:</sel>
          <arg type="uint32_t">c</arg>
          <sel>name:</sel>
          <arg type="NSString*">n</arg>
          <desc>
            Initialises the receiver as a multi-producer,
            multi-consumer FIFO with no timeout and with
            default stats gathering enabled. <br /> However,
            these values (including the supplied capacity) may be
            overridden as specified in
            <ref type="method" id="-initWithName:">
              -initWithName:
            </ref>
          </desc>
        </method>
        <method type="id">
          <sel>initWithName:</sel>
          <arg type="NSString*">n</arg>
          <desc>
            Initialises the receiver using the specified
            name and obtaining other details from the
            NSUserDefaults system using defaults keys
            where 'NNN' is the supplied name. <br /> The
            GSFIFOCapacityNNN default specifies the
            capacity for the FIFO, and if missing a capacity
            of 1000 is assumed. <br /> The GSFIFOGranularityNNN
            integer is zero by default. <br /> The
            GSFIFOTimeoutNNN integer is zero by
            default. <br /> The GSFIFOSingleConsumerNNN
            boolean is <code>NO</code> by default. <br /> The
            GSFIFOSingleProducerNNN boolean is
            <code>NO</code> by default. <br /> The
            GSFIFOBoundariesNNN array is missing by
            default. <br />
          </desc>
        </method>
        <method type="void">
          <sel>put:</sel>
          <arg type="void*">item</arg>
          <desc>
            Adds an <var>item</var> to the FIFO, blocking if
            necessary until there is space in the buffer.
            Raises an exception if the FIFO is configured with a
            timeout and it is exceeded.br /> Implemented using
            <ref type="method" id="-put:count:shouldBlock:">
              -put:count:shouldBlock:
            </ref>
          </desc>
        </method>
        <method type="unsigned">
          <sel>put:</sel>
          <arg type="void**">buf</arg>
          <sel>count:</sel>
          <arg type="unsigned">count</arg>
          <sel>shouldBlock:</sel>
          <arg type="BOOL">block</arg>
          <desc>
            Writes up to <var>count</var> items from
            <var>buf</var> into the FIFO. If <var>block</var> is
            <code>YES</code>, this blocks if necessary until at
            least one item can be written, and raises an
            exception if the FIFO is configured with a
            timeout and it is exceeded. <br /> Returns the
            number of items actually written.
          </desc>
        </method>
        <method type="NSString*">
          <sel>stats</sel>
          <desc>
            Return any available statistics for the receiver.
            <br />
          </desc>
        </method>
        <method type="NSString*">
          <sel>statsGet</sel>
          <desc>
            Return statistics on get operations for the
            receiver. <br /> NB. If the recever is not
            configured for multiple consumers, this method
            may only be called from the single consumer thread.
          </desc>
        </method>
        <method type="NSString*">
          <sel>statsPut</sel>
          <desc>
            Return statistics on put operations for the
            receiver. <br /> NB. If the recever is not
            configured for multiple producers, this method
            may only be called from the single producer thread.
          </desc>
        </method>
        <method type="void*">
          <sel>tryGet</sel>
          <desc>
            Checks the FIFO and returns the first available item
            or NULL if the FIFO is empty. <br /> Implemented using
            <ref type="method" id="-get:count:shouldBlock:">
              -get:count:shouldBlock:
            </ref>
          </desc>
        </method>
        <method type="BOOL">
          <sel>tryPut:</sel>
          <arg type="void*">item</arg>
          <desc>
            Attempts to put an <var>item</var> into the FIFO,
            returning <code>YES</code> on success or
            <code>NO</code> if the FIFO is full. <br />
            Implemented using
            <ref type="method" id="-put:count:shouldBlock:">
              -put:count:shouldBlock:
            </ref>
          </desc>
        </method>
      </class>
    </chapter>
    <chapter>
      <heading>GSFIFO functions</heading>
      <p></p>
      <function type="void*" name="GSGetFastFIFO">
        <arg type="GSFIFO*">receiver</arg>
        <desc>
          Function to efficiently get an item from a fast
          FIFO, blocking if necessary until an item is available
          or the timeout occurs. <br /> Warning... only for use if
          the FIFO is NOT configured for multiple consumers.
        </desc>
      </function>
      <function type="void*" name="GSGetFastNonBlockingFIFO">
        <arg type="GSFIFO*">receiver</arg>
        <desc>
          Function to efficiently get an item from a fast
          FIFO. <br /> Returns NULL if the FIFO is empty. <br />
          Warning... only for use if the FIFO is NOT configured
          for multiple consumers.
        </desc>
      </function>
      <function type="void" name="GSPutFastFIFO">
        <arg type="GSFIFO*">receiver</arg>
        <arg type="void*">item</arg>
        <desc>
          Function to efficiently put an <var>item</var> to a
          fast FIFO, blocking if necessary until there is space in
          the FIFO or until the timeout occurs. <br /> Warning...
          only for use if the FIFO is NOT configured for multiple
          producers.
        </desc>
      </function>
      <function type="BOOL" name="GSPutFastNonBlockingFIFO">
        <arg type="GSFIFO*">receiver</arg>
        <arg type="void*">item</arg>
        <desc>
          Function to efficiently put an <var>item</var> to a
          fast FIFO. <br /> Returns <code>YES</code> on success,
          <code>NO</code> on failure (FIFO is full). <br />
          Warning... only for use if the FIFO is NOT configured
          for multiple producers.
        </desc>
      </function>
    </chapter>
  </body>
</gsdoc>
