## gnome-vfs-module-callback gnome-vfs-module-callback — functions used by apps if they want to answer to callback invocations by gnome-vfs modules |

## Synopsis

    void        (*GnomeVFSModuleCallback)       (gconstpointer in,
                                                 gsize in_size,
                                                 gpointer out,
                                                 gsize out_size,
                                                 gpointer callback_data);
    void        (*GnomeVFSModuleCallbackResponse)
                                                (gpointer response_data);
    void        (*GnomeVFSAsyncModuleCallback)  (gconstpointer in,
                                                 gsize in_size,
                                                 gpointer out,
                                                 gsize out_size,
                                                 gpointer callback_data,
                                                 GnomeVFSModuleCallbackResponse response,
                                                 gpointer response_data);
    void        gnome_vfs_module_callback_set_default
                                                (const char *callback_name,
                                                 GnomeVFSModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);
    void        gnome_vfs_module_callback_push  (const char *callback_name,
                                                 GnomeVFSModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);
    void        gnome_vfs_module_callback_pop   (const char *callback_name);
    void        gnome_vfs_async_module_callback_set_default
                                                (const char *callback_name,
                                                 GnomeVFSAsyncModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);
    void        gnome_vfs_async_module_callback_push
                                                (const char *callback_name,
                                                 GnomeVFSAsyncModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);
    void        gnome_vfs_async_module_callback_pop
                                                (const char *callback_name);

## Description

## Details

### GnomeVFSModuleCallback ()

    void        (*GnomeVFSModuleCallback)       (gconstpointer in,
                                                 gsize in_size,
                                                 gpointer out,
                                                 gsize out_size,
                                                 gpointer callback_data);

This is the type of a callback function that gets set for a module callback.

When the callback is invoked, the user function is called with an `in` argument, the exact type of which depends on the specific callback. It is generally a pointer to a struct with several fields that provide information to the callback.

The `out` argument is used to return a value from the callback. Once again the exact type depends on the specific callback. It is generally a pointer to a pre-allocated struct with several fields that the callback function should fill in before returning.

`in` : | in argument for this callback; the exact type depends on the specific callback.
`in_size` : | size of the in argument; useful for sanity-checking.
`out` : | out argument for this callback; the exact type depends on the specific callback.
`out_size` : | size of the out argument; useful for sanity-checking.
`callback_data` : | callback data specified when this callback was set.

### GnomeVFSModuleCallbackResponse ()

    void        (*GnomeVFSModuleCallbackResponse)
                                                (gpointer response_data);

This is the type of the response function passed to a `GnomeVFSAsyncModuleCallback()`. It should be called when the async callback has completed.

`response_data` : | pass the response data argument originally passed to the async callback.

### GnomeVFSAsyncModuleCallback ()

    void        (*GnomeVFSAsyncModuleCallback)  (gconstpointer in,
                                                 gsize in_size,
                                                 gpointer out,
                                                 gsize out_size,
                                                 gpointer callback_data,
                                                 GnomeVFSModuleCallbackResponse response,
                                                 gpointer response_data);

This is the type of a callback function that gets set for an async module callback.

Such callbacks are useful when you are using the API and want callbacks to be handled from the main thread, for instance if they need to put up a dialog.

Like a `GnomeVFSModuleCallback()`, an async callback has `in` and `out` arguments for passing data into and out of the callback. However, an async callback does not need to fill in the `out` argument before returning. Instead, it can arrange to have the work done from a callback on the main loop, from another thread, etc. The `response` function should be called by whatever code finishes the work of the callback with `response_data` as an argument once the `out` argument is filled in and the callback is done.

The `in` and `out` arguments are guaranteed to remain valid until the `response` function is called.

`in` : | in argument for this callback; the exact type depends on the specific callback.
`in_size` : | size of the in argument; useful for sanity-checking.
`out` : | out argument for this callback; the exact type depends on the specific callback.
`out_size` : | size of the out argument; useful for sanity-checking.
`callback_data` : | The `callback_data` specified when this callback was set.
`response` : | response function to call when the callback is completed.
`response_data` : | argument to pass to `response`.

### gnome_vfs_module_callback_set_default ()

    void        gnome_vfs_module_callback_set_default
                                                (const char *callback_name,
                                                 GnomeVFSModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);

Set the default callback for `callback_name` to `callback`. `callback` will be called with `callback_data` on the same thread as the gnome-vfs operation that invokes it. The default value is shared for all threads, but setting it is thread-safe.

Use this function if you want to set a handler to be used by your whole application. You can use `gnome_vfs_module_callback_push()` to set a callback function that will temporarily override the default on the current thread instead. Or you can also use `gnome_vfs_async_module_callback_set_default()` to set an async callback function.

Note: `destroy_notify` may be called on any thread - it is not guaranteed to be called on the main thread.

`callback_name` : | name of the module callback to set.
`callback` : | function to call when the `callback` is invoked.
`callback_data` : | data to pass to `callback`.
`destroy_notify` : | function to call when `callback_data` is to be freed.

### gnome_vfs_module_callback_push ()

    void        gnome_vfs_module_callback_push  (const char *callback_name,
                                                 GnomeVFSModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);

Set `callback` as a temprary handler for `callback_name`. `callback` will be called with `callback_data` on the same thread as the gnome-vfs operation that invokes it. The temporary handler is set per-thread.

`gnome_vfs_module_callback_pop()` removes the most recently set temporary handler. The temporary handlers are treated as a first-in first-out stack.

Use this function to set a temporary callback handler for a single call or a few calls. You can use `gnome_vfs_module_callback_set_default()` to set a callback function that will establish a permanent global setting for all threads instead.

Note: `destroy_notify` may be called on any thread - it is not guaranteed to be called on the main thread.

`callback_name` : | name of the module callback to set temporarily.
`callback` : | function to call when the `callback` is invoked.
`callback_data` : | data to pass to `callback`.
`destroy_notify` : | function to call when `callback_data` is to be freed.

### gnome_vfs_module_callback_pop ()

    void        gnome_vfs_module_callback_pop   (const char *callback_name);

Remove the temporary handler for `callback_name` most recently set with `gnome_vfs_module_callback_push()`. If another temporary handler was previously set on the same thread, it becomes the current handler. Otherwise, the default handler, if any, becomes current.

The temporary handlers are treated as a first-in first-out stack.

`callback_name` : | name of the module callback to remove a temporary handler for.

### gnome_vfs_async_module_callback_set_default ()

    void        gnome_vfs_async_module_callback_set_default
                                                (const char *callback_name,
                                                 GnomeVFSAsyncModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);

Set the default async callback for `callback_name` to `callback`. `callback` will be called with `callback_data` from a callback on the main thread. It will be passed a response function which should be called to signal completion of the callback. The callback function itself may return in the meantime.

The default value is shared for all threads, but setting it is thread-safe.

Use this function if you want to globally set a callback handler for use with async operations.

You can use `gnome_vfs_async_module_callback_push()` to set an async callback function that will temporarily override the default on the current thread instead. Or you can also use `gnome_vfs_module_callback_set_default()` to set a regular callback function.

Note: `destroy_notify` may be called on any thread - it is not guaranteed to be called on the main thread.

`callback_name` : | name of the async module callback to set.
`callback` : | function to call when `callback` is invoked.
`callback_data` : | data to pass to `callback`.
`destroy_notify` : | function to call when `callback_data` is to be freed.

### gnome_vfs_async_module_callback_push ()

    void        gnome_vfs_async_module_callback_push
                                                (const char *callback_name,
                                                 GnomeVFSAsyncModuleCallback callback,
                                                 gpointer callback_data,
                                                 GDestroyNotify destroy_notify);

Set `callback` as a temprary async handler for `callback_name`. `callback` will be called with `callback_data` from a callback on the main thread. It will be passed a response function which should be called to signal completion of the callback. The callback function itself may return in the meantime.

The temporary async handler is set per-thread.

`gnome_vfs_async_module_callback_pop()` removes the most recently set temporary handler. The temporary async handlers are treated as a first-in first-out stack.

Use this function to set a temporary async callback handler for a single call or a few calls. You can use `gnome_vfs_async_module_callback_set_default()` to set an async callback function that will establish a permanent global setting for all threads instead.

Note: `destroy_notify` may be called on any thread - it is not guaranteed to be called on the main thread.

`callback_name` : | name of the module callback to set temporarily.
`callback` : | function to call when `callback` is invoked.
`callback_data` : | data to pass to `callback`.
`destroy_notify` : | function to call when `callback_data` is to be freed.

### gnome_vfs_async_module_callback_pop ()

    void        gnome_vfs_async_module_callback_pop
                                                (const char *callback_name);

Remove the temporary async handler for `callback_name` most recently set with `gnome_vfs_async_module_callback_push()`. If another temporary async handler was previously set on the same thread, it becomes the current handler. Otherwise, the default async handler, if any, becomes current.

The temporary async handlers are treated as a first-in first-out stack.

`callback_name` : | name of the module callback to remove a temporary handler for.