## Hook Functions

Hook Functions — support for manipulating lists of hook functions.

## Synopsis

    #include <glib.h>

    struct      GHookList;
    void        (*GHookFinalizeFunc)            (GHookList *hook_list,
                                                 GHook *hook);
    struct      GHook;
    void        (*GHookFunc)                    (gpointer data);
    gboolean    (*GHookCheckFunc)               (gpointer data);

    void        g_hook_list_init                (GHookList *hook_list,
                                                 guint hook_size);
    void        g_hook_list_invoke              (GHookList *hook_list,
                                                 gboolean may_recurse);
    void        g_hook_list_invoke_check        (GHookList *hook_list,
                                                 gboolean may_recurse);
    void        g_hook_list_marshal             (GHookList *hook_list,
                                                 gboolean may_recurse,
                                                 GHookMarshaller marshaller,
                                                 gpointer marshal_data);
    void        (*GHookMarshaller)              (GHook *hook,
                                                 gpointer marshal_data);
    void        g_hook_list_marshal_check       (GHookList *hook_list,
                                                 gboolean may_recurse,
                                                 GHookCheckMarshaller marshaller,
                                                 gpointer marshal_data);
    gboolean    (*GHookCheckMarshaller)         (GHook *hook,
                                                 gpointer marshal_data);
    void        g_hook_list_clear               (GHookList *hook_list);

    GHook*      g_hook_alloc                    (GHookList *hook_list);
    #define     g_hook_append                   ( hook_list, hook )
    void        g_hook_prepend                  (GHookList *hook_list,
                                                 GHook *hook);
    void        g_hook_insert_before            (GHookList *hook_list,
                                                 GHook *sibling,
                                                 GHook *hook);
    void        g_hook_insert_sorted            (GHookList *hook_list,
                                                 GHook *hook,
                                                 GHookCompareFunc func);
    gint        (*GHookCompareFunc)             (GHook *new_hook,
                                                 GHook *sibling);
    gint        g_hook_compare_ids              (GHook *new_hook,
                                                 GHook *sibling);

    GHook*      g_hook_get                      (GHookList *hook_list,
                                                 gulong hook_id);
    GHook*      g_hook_find                     (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 GHookFindFunc func,
                                                 gpointer data);
    gboolean    (*GHookFindFunc)                (GHook *hook,
                                                 gpointer data);
    GHook*      g_hook_find_data                (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 gpointer data);
    GHook*      g_hook_find_func                (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 gpointer func);
    GHook*      g_hook_find_func_data           (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 gpointer func,
                                                 gpointer data);

    GHook*      g_hook_first_valid              (GHookList *hook_list,
                                                 gboolean may_be_in_call);
    GHook*      g_hook_next_valid               (GHookList *hook_list,
                                                 GHook *hook,
                                                 gboolean may_be_in_call);
    enum        GHookFlagMask;
    #define     G_HOOK_FLAGS                    (hook)
    #define     G_HOOK_FLAG_USER_SHIFT

    #define     G_HOOK                          (hook)
    #define     G_HOOK_IS_VALID                 (hook)
    #define     G_HOOK_ACTIVE                   (hook)
    #define     G_HOOK_IN_CALL                  (hook)
    #define     G_HOOK_IS_UNLINKED              (hook)

    void        g_hook_ref                      (GHookList *hook_list,
                                                 GHook *hook);
    void        g_hook_unref                    (GHookList *hook_list,
                                                 GHook *hook);
    void        g_hook_free                     (GHookList *hook_list,
                                                 GHook *hook);
    gboolean    g_hook_destroy                  (GHookList *hook_list,
                                                 gulong hook_id);
    void        g_hook_destroy_link             (GHookList *hook_list,
                                                 GHook *hook);

## Description

The GHookList, GHook and their related functions provide support for lists of hook functions. Functions can be added and removed from the lists, and the list of hook functions can be invoked.

## Details

### struct GHookList

    struct GHookList {

      gulong	    seq_id;
      guint		    hook_size : 16;
      guint		    is_setup : 1;
      GHook		   *hooks;
      GMemChunk	   *hook_memchunk;
      GHookFinalizeFunc finalize_hook;
      gpointer	    dummy[2];
    };

The GHookList struct represents a list of hook functions.

gulong `seq_id` | the next free GHook id.
guint `hook_size` : 16 | the size of the GHookList elements, in bytes.
guint `is_setup` : 1 | 1 if the GHookList has been initialized.
GHook *`hooks` | the first GHook element in the list.
GMemChunk *`hook_memchunk` | the GMemChunk used for allocating the GHook elements.
GHookFinalizeFunc `finalize_hook` | the function to call to finalize a GHook element. The default behaviour is to call the hooks `destroy` function.
gpointer `dummy`[2] |

### GHookFinalizeFunc ()

    void        (*GHookFinalizeFunc)            (GHookList *hook_list,
                                                 GHook *hook);

Defines the type of function to be called when a hook in a list of hooks gets finalized.

`hook_list` : | a GHookList.
`hook` : | the hook in `hook_list` that gets finalized.

### struct GHook

    struct GHook {

      gpointer	 data;
      GHook		*next;
      GHook		*prev;
      guint		 ref_count;
      gulong	 hook_id;
      guint		 flags;
      gpointer	 func;
      GDestroyNotify destroy;
    };

The GHook struct represents a single hook function in a GHookList.

gpointer `data` | data which is passed to func when this hook is invoked.
GHook *`next` | pointer to the next hook in the list.
GHook *`prev` | pointer to the previous hook in the list.
guint `ref_count` | the reference count of this hook.
gulong `hook_id` | the id of this hook, which is unique within its list.
guint `flags` | flags which are set for this hook. See GHookFlagMask for predefined flags.
gpointer `func` | the function to call when this hook is invoked. The possible signatures for this function are GHookFunc and GHookCheckFunc.
GDestroyNotify `destroy` | the default `finalize_hook` function of a GHookList calls this member of the hook that is being finalized.

### GHookFunc ()

    void        (*GHookFunc)                    (gpointer data);

Defines the type of a hook function that can be invoked by `g_hook_list_invoke()`.

`data` : | the data field of the GHook is passed to the hook function here.

### GHookCheckFunc ()

    gboolean    (*GHookCheckFunc)               (gpointer data);

Defines the type of a hook function that can be invoked by `g_hook_list_invoke_check()`.

`data` : | the data field of the GHook is passed to the hook function here.
Returns : | `FALSE` if the GHook should be destroyed.

### g_hook_list_init ()

    void        g_hook_list_init                (GHookList *hook_list,
                                                 guint hook_size);

Initializes a GHookList. This must be called before the GHookList is used.

`hook_list` : | a GHookList.
`hook_size` : | the size of each element in the GHookList, typically `sizeof (GHook)`.

### g_hook_list_invoke ()

    void        g_hook_list_invoke              (GHookList *hook_list,
                                                 gboolean may_recurse);

Calls all of the GHook functions in a GHookList.

`hook_list` : | a GHookList.
`may_recurse` : | `TRUE` if functions which are already running (e.g. in another thread) can be called. If set to `FALSE`, these are skipped.

### g_hook_list_invoke_check ()

    void        g_hook_list_invoke_check        (GHookList *hook_list,
                                                 gboolean may_recurse);

Calls all of the GHook functions in a GHookList. Any function which returns `TRUE` is removed from the GHookList.

`hook_list` : | a GHookList.
`may_recurse` : | `TRUE` if functions which are already running (e.g. in another thread) can be called. If set to `FALSE`, these are skipped.

### g_hook_list_marshal ()

    void        g_hook_list_marshal             (GHookList *hook_list,
                                                 gboolean may_recurse,
                                                 GHookMarshaller marshaller,
                                                 gpointer marshal_data);

Calls a function on each valid GHook.

`hook_list` : | a GHookList.
`may_recurse` : | `TRUE` if hooks which are currently running (e.g. in another thread) are considered valid. If set to `FALSE`, these are skipped.
`marshaller` : | the function to call for each GHook.
`marshal_data` : | data to pass to `marshaller`.

### GHookMarshaller ()

    void        (*GHookMarshaller)              (GHook *hook,
                                                 gpointer marshal_data);

Defines the type of function used by `g_hook_list_marshal()`.

`hook` : | a GHook.
`marshal_data` : | user data.

### g_hook_list_marshal_check ()

    void        g_hook_list_marshal_check       (GHookList *hook_list,
                                                 gboolean may_recurse,
                                                 GHookCheckMarshaller marshaller,
                                                 gpointer marshal_data);

Calls a function on each valid GHook and destroys it if the function returns `FALSE`.

`hook_list` : | a GHookList.
`may_recurse` : | `TRUE` if hooks which are currently running (e.g. in another thread) are considered valid. If set to `FALSE`, these are skipped.
`marshaller` : | the function to call for each GHook.
`marshal_data` : | data to pass to `marshaller`.

### GHookCheckMarshaller ()

    gboolean    (*GHookCheckMarshaller)         (GHook *hook,
                                                 gpointer marshal_data);

Defines the type of function used by `g_hook_list_marshal_check()`.

`hook` : | a GHook.
`marshal_data` : | user data.
Returns : | `FALSE` if `hook` should be destroyed.

### g_hook_list_clear ()

    void        g_hook_list_clear               (GHookList *hook_list);

Removes all the GHook elements from a GHookList.

`hook_list` : | a GHookList.

### g_hook_alloc ()

    GHook*      g_hook_alloc                    (GHookList *hook_list);

Allocates space for a GHook and initializes it.

`hook_list` : | a GHookList.
Returns : | a new GHook.

### g_hook_append()

    #define     g_hook_append( hook_list, hook )

Appends a GHook onto the end of a GHookList.

`hook_list` : | a GHookList.
`hook` : | the GHook to add to the end of `hook_list`.

### g_hook_prepend ()

    void        g_hook_prepend                  (GHookList *hook_list,
                                                 GHook *hook);

Prepends a GHook on the start of a GHookList.

`hook_list` : | a GHookList.
`hook` : | the GHook to add to the start of `hook_list`.

### g_hook_insert_before ()

    void        g_hook_insert_before            (GHookList *hook_list,
                                                 GHook *sibling,
                                                 GHook *hook);

Inserts a GHook into a GHookList, before a given GHook.

`hook_list` : | a GHookList.
`sibling` : | the GHook to insert the new GHook before.
`hook` : | the GHook to insert.

### g_hook_insert_sorted ()

    void        g_hook_insert_sorted            (GHookList *hook_list,
                                                 GHook *hook,
                                                 GHookCompareFunc func);

Inserts a GHook into a GHookList, sorted by the given function.

`hook_list` : | a GHookList.
`hook` : | the GHook to insert.
`func` : | the comparison function used to sort the GHook elements.

### GHookCompareFunc ()

    gint        (*GHookCompareFunc)             (GHook *new_hook,
                                                 GHook *sibling);

Defines the type of function used to compare GHook elements in `g_hook_insert_sorted()`.

`new_hook` : | the GHook being inserted.
`sibling` : | the GHook to compare with `new_hook`.
Returns : | a value <= 0 if `new_hook` should be before `sibling`.

### g_hook_compare_ids ()

    gint        g_hook_compare_ids              (GHook *new_hook,
                                                 GHook *sibling);

Compares the ids of two GHook elements, returning a negative value if the second id is greater than the first.

`new_hook` : | a GHook.
`sibling` : | a GHook to compare with `new_hook`.
Returns : | a value <= 0 if the id of `sibling` is >= the id of `new_hook`.

### g_hook_get ()

    GHook*      g_hook_get                      (GHookList *hook_list,
                                                 gulong hook_id);

Returns the GHook with the given id, or `NULL` if it is not found.

`hook_list` : | a GHookList.
`hook_id` : | a hook id.
Returns : | the GHook with the given id, or `NULL` if it is not found.

### g_hook_find ()

    GHook*      g_hook_find                     (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 GHookFindFunc func,
                                                 gpointer data);

Finds a GHook in a GHookList using the given function to test for a match.

`hook_list` : | a GHookList.
`need_valids` : | `TRUE` if GHook elements which have been destroyed should be skipped.
`func` : | the function to call for each GHook, which should return `TRUE` when the GHook has been found.
`data` : | the data to pass to `func`.
Returns : | the found GHook or `NULL` if no matching GHook is found.

### GHookFindFunc ()

    gboolean    (*GHookFindFunc)                (GHook *hook,
                                                 gpointer data);

Defines the type of the function passed to `g_hook_find()`.

`hook` : | a GHook.
`data` : | user data passed to `g_hook_find_func()`.
Returns : | `TRUE` if the required GHook has been found.

### g_hook_find_data ()

    GHook*      g_hook_find_data                (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 gpointer data);

Finds a GHook in a GHookList with the given data.

`hook_list` : | a GHookList.
`need_valids` : | `TRUE` if GHook elements which have been destroyed should be skipped.
`data` : | the data to find.
Returns : | the GHook with the given `data` or `NULL` if no matching GHook is found.

### g_hook_find_func ()

    GHook*      g_hook_find_func                (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 gpointer func);

Finds a GHook in a GHookList with the given function.

`hook_list` : | a GHookList.
`need_valids` : | `TRUE` if GHook elements which have been destroyed should be skipped.
`func` : | the function to find.
Returns : | the GHook with the given `func` or `NULL` if no matching GHook is found.

### g_hook_find_func_data ()

    GHook*      g_hook_find_func_data           (GHookList *hook_list,
                                                 gboolean need_valids,
                                                 gpointer func,
                                                 gpointer data);

Finds a GHook in a GHookList with the given function and data.

`hook_list` : | a GHookList.
`need_valids` : | `TRUE` if GHook elements which have been destroyed should be skipped.
`func` : | the function to find.
`data` : | the data to find.
Returns : | the GHook with the given `func` and `data` or `NULL` if no matching GHook is found.

### g_hook_first_valid ()

    GHook*      g_hook_first_valid              (GHookList *hook_list,
                                                 gboolean may_be_in_call);

Returns the first GHook in a GHookList which has not been destroyed. The reference count for the GHook is incremented, so you must call `g_hook_unref()` to restore it when no longer needed. (Or call `g_hook_next_valid()` if you are stepping through the GHookList.)

`hook_list` : | a GHookList.
`may_be_in_call` : | `TRUE` if hooks which are currently running (e.g. in another thread) are considered valid. If set to `FALSE`, these are skipped.
Returns : | the first valid GHook, or `NULL` if none are valid.

### g_hook_next_valid ()

    GHook*      g_hook_next_valid               (GHookList *hook_list,
                                                 GHook *hook,
                                                 gboolean may_be_in_call);

Returns the next GHook in a GHookList which has not been destroyed. The reference count for the GHook is incremented, so you must call `g_hook_unref()` to restore it when no longer needed. (Or continue to call `g_hook_next_valid()` until `NULL` is returned.)

`hook_list` : | a GHookList.
`hook` : | the current GHook.
`may_be_in_call` : | `TRUE` if hooks which are currently running (e.g. in another thread) are considered valid. If set to `FALSE`, these are skipped.
Returns : | the next valid GHook, or `NULL` if none are valid.

### enum GHookFlagMask

    typedef enum
    {
      G_HOOK_FLAG_ACTIVE	    = 1 << 0,
      G_HOOK_FLAG_IN_CALL	    = 1 << 1,
      G_HOOK_FLAG_MASK	    = 0x0f
    } GHookFlagMask;

Flags used internally in the GHook implementation.

`G_HOOK_FLAG_ACTIVE` | set if the hook has not been destroyed.
`G_HOOK_FLAG_IN_CALL` | set if the hook is currently being run.
`G_HOOK_FLAG_MASK` |

### G_HOOK_FLAGS()

    #define	G_HOOK_FLAGS(hook)		(G_HOOK (hook)->flags)

Returns the flags of a hook.

`hook` : | a GHook.

### G_HOOK_FLAG_USER_SHIFT

    #define G_HOOK_FLAG_USER_SHIFT	(4)

The position of the first bit which is not reserved for internal use be the GHook implementation, i.e. `1 << G_HOOK_FLAG_USER_SHIFT` is the first bit which can be used for application-defined flags.

### G_HOOK()

    #define	G_HOOK(hook)			((GHook*) (hook))

Casts a pointer to a `GHook*`.

`hook` : | a pointer.

### G_HOOK_IS_VALID()

    #define     G_HOOK_IS_VALID(hook)

Returns `TRUE` if the GHook is valid, i.e. it is in a GHookList, it is active and it has not been destroyed.

`hook` : | a GHook.
Returns : | `TRUE` if the GHook is valid.

### G_HOOK_ACTIVE()

    #define     G_HOOK_ACTIVE(hook)

Returns `TRUE` if the GHook is active, which is normally `TRUE` until the GHook is destroyed.

`hook` : | a GHook.
Returns : | `TRUE` if the GHook is active.

### G_HOOK_IN_CALL()

    #define     G_HOOK_IN_CALL(hook)

Returns `TRUE` if the GHook function is currently executing.

`hook` : | a GHook.
Returns : | `TRUE` if the GHook function is currently executing.

### G_HOOK_IS_UNLINKED()

    #define     G_HOOK_IS_UNLINKED(hook)

Returns `TRUE` if the GHook is not in a GHookList.

`hook` : | a GHook.
Returns : | `TRUE` if the GHook is not in a GHookList.

### g_hook_ref ()

    void        g_hook_ref                      (GHookList *hook_list,
                                                 GHook *hook);

Increments the reference count for a GHook.

`hook_list` : | a GHookList.
`hook` : | the GHook to increment the reference count of.

### g_hook_unref ()

    void        g_hook_unref                    (GHookList *hook_list,
                                                 GHook *hook);

Decrements the reference count of a GHook. If the reference count falls to 0, the GHook is removed from the GHookList and `g_hook_free()` is called to free it.

`hook_list` : | a GHookList.
`hook` : | the GHook to unref.

### g_hook_free ()

    void        g_hook_free                     (GHookList *hook_list,
                                                 GHook *hook);

Calls the GHookList `hook_free` function if it exists, and frees the memory allocated for the GHook.

`hook_list` : | a GHookList.
`hook` : | the GHook to free.

### g_hook_destroy ()

    gboolean    g_hook_destroy                  (GHookList *hook_list,
                                                 gulong hook_id);

Destroys a GHook, given its ID.

`hook_list` : | a GHookList.
`hook_id` : | a hook ID.
Returns : | `TRUE` if the GHook was found in the GHookList and destroyed.

### g_hook_destroy_link ()

    void        g_hook_destroy_link             (GHookList *hook_list,
                                                 GHook *hook);

Removes one GHook from a GHookList, marking it inactive and calling `g_hook_unref()` on it.

`hook_list` : | a GHookList.
`hook` : | the GHook to remove.