93 lines
2.6 KiB
Plaintext
93 lines
2.6 KiB
Plaintext
How ref counting works within Gdk and Gtk
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=========================================
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Each data structure that provides ref counting offers a bunch of
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functions that follow these conventions:
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*_new: Create a new structure with a reference count of 1.
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*_ref: Increase ref count by one.
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*_unref: Decrease ref count by one. If the count drops to zero,
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free the memory. No user visible actions should take place,
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like destryoing windows, etc.
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Some structures also provide a *_destroy function.
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GdkWindow
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---------
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A GdkWindow has to be explicitely destroyed with gdk_window_destroy.
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This will send out a request to destroy this window and all its
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children, and will decrement the ref_count of the GdkWindow by one.
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Thus, it releases the inital reference created by gdk_window_new.
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All GdkWindows are kept in a hash table to translate from their XId to
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the actual structure and the pointer in the hash table is reflected in
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the reference count. When a DestroyNotify event is received for a
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particular GdkWindow, it is removed from the hash table and the
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ref_count is updated accordingly.
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You can call gdk_window_destroy more than once on a particular
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GdkWindow, it will only be destroyed when it hasn't been yet. The
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ref_count is *always* decremented, tho.
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GdkPixmap
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---------
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There is no gdk_pixmap_destroy function. The Pixmap is destroyed when
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the last reference to it vanishes.
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GdkPixmaps are kept in the same hash table as GdkWindows but the
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pointer in the hash table is *not* reflected in the ref_count.
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This works only when Pixmaps never get XEvents. I'm not sure if this
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is the case.
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GdkBitmap
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---------
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A GdkBitmap is only another name for a special use of GdkPixmap.
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GdkVisual
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---------
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There are no *_new or *_destroy functions and the *_ref and *_unref
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functions are noops. GdkVisuals are static structures and thus do not
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need reference counting. The ref counting functions are only there
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for extra defensive programming.
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GdkColormap
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-----------
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Nothing special. There is no gdk_colormap_destroy function.
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GdkFont / GdkFontSet
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--------------------
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GdkFont and GdkFontSet are equivalent as far as ref counting is
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concerned. Use gdk_font_ref and gdk_font_unref for both.
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There is no gdk_font_free or gdk_fontset_free function.
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GtkAcceleratorTable
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-------------------
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There is no gtk_accelerator_table_destroy function.
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GtkTooltips
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-----------
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There is no gtk_tooltips_destroy function.
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GtkStyle
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--------
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There is no gtk_style_destroy function.
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GtkObject
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---------
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This one is the most tricky and I'm still meditating over it.
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- Marius Vollmer <mvo@zagadka.ping.de>
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