gtk2/docs/reference/gdk-pixbuf/tmpl/refcounting.sgml

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Reference Counting and Memory Mangement

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Functions to perform reference counting and memory management on a
#GdkPixbuf.

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  <para>
    #GdkPixbuf structures are reference counted.  This means that
    an application can share a single pixbuf among many parts of the
    code.  When a piece of the program needs to keep a pointer to a
    pixbuf, it should add a reference to it.  When it no longer needs
    the pixbuf, it should subtract a reference.  The pixbuf will be
    destroyed when its reference count drops to zero.  Newly-created
    #GdkPixbuf structures start with a reference count of one.
  </para>

  <para>
    <emphasis>Finalizing</emphasis> a pixbuf means to free its pixel
    data and to free the #GdkPixbuf structure itself.  Most of the
    library functions that create #GdkPixbuf structures create the
    pixel data by themselves and define the way it should be freed;
    you do not need to worry about those.  The only function that lets
    you specify how to free the pixel data is
    gdk_pixbuf_new_from_data().  Since you pass it a pre-allocated
    pixel buffer, you must also specify a way to free that data.  This
    is done with a function of type #GdkPixbufDestroyNotify.  When a
    pixbuf created with gdk_pixbuf_new_from_data() is finalized, your
    destroy notification function will be called, and it is its
    responsibility to free the pixel array.
  </para>

  <para>
    As an extension to traditional reference counting, #GdkPixbuf
    structures support defining a handler for the last unref
    operation.  If gdk_pixbuf_unref() is called on a #GdkPixbuf
    structure that has a reference count of 1, i.e. its last
    reference, then the pixbuf's last unref handler function will be
    called.  It is up to this function to determine whether to
    finalize the pixbuf using gdk_pixbuf_finalize() or to just
    continue execution.  This can be used to implement a pixbuf cache
    efficiently; please see the programmer's documentation for
    details.
  </para>

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  <para>
    #GdkPixbuf, gdk_pixbuf_new_from_data().
  </para>