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This manual documents MIT/GNU Scheme Pucked GLib 0.14.
Copyright © 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 Matthew Birkholz
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”
| • Introduction: | ||
| • API Reference: | ||
| • Implementation Notes: | This is for Scheme widget developers. | |
| • GNU Free Documentation License: |
Next: API Reference, Previous: Top, Up: Top
The GLib system is a collection of Scheme data types and procedures providing a Schemely interface to the GLib, GObject and GIO libraries. It is used by the GStreamer and Gtk plugins. Very little of the libraries’ APIs has been wrapped — just what is listed herein. As one might expect of a “Schemely” interface, all toolkit resources are protected from “leaking” by the garbage collector. When Scheme’s representative of a toolkit resource is dropped and collected, the toolkit resource is freed, just as the C/Unix FFI’s malloced aliens are automatically freed.
The GLib library, and thus libraries build “on top” of GLib, are not
ready for multiple threads. This is not an issue in single-processing
worlds, but future multi-processing worlds will need to ensure that
just one Scheme thread is “in” the toolkits. As of version 0.7, the
with-glib-lock procedure is provided. It serializes access to
the toolkits by locking a mutex. If the current thread has not used
this procedure to lock GLib, every callout to the toolkits will write
a warning line to stderr.
Callbacks occur during callouts and execute while GLib is locked
(assuming GLib was locked when the callout was made). Thus using
with-glib-lock in a callback will cause a deadlock.
Locks GLib’s mutex for the duration of thunk. Thus this procedure cannot be used inside thunk or the current thread will deadlock in the attempt to lock GLib’s mutex twice.
Invokes thunk after releasing the current thread’s lock on GLib’s mutex, and acquires a lock again before returning.
| • API Reference: | ||
| • GObject: | ||
| • GIO: | ||
| • Debugging Facilities: |
Next: Implementation Notes, Previous: Introduction, Up: Top
Most of the GLib system’s public bindings are in the (glib)
package — not exported to the global environment. It is assumed
that other systems will import bindings from (glib) or create
child packages (e.g. a GLib child that exports its entry points by
adding procedures to generics imported from a more abstract package).
| • GObject: | ||
| • GIO: | ||
| • Debugging Facilities: |
Next: GIO, Previous: API Reference, Up: API Reference
An instance of <gobject> represents a reference to a toolkit
object, typically one created by Scheme. The instance is “live”
while Scheme holds the reference. gobject-unref! kills it,
releasing Scheme’s reference. Once dead to Scheme, the toolkit may
dispose and finalize the GObject.
Callbacks can be "connected" to gobjects — one callback per signal name. The procedures run without-interrupts (or at least without-preemption, or perhaps just without-toolkit). Connecting a second callback disconnects the first.
All connected callbacks are “pinned” by the
registered-callbacks vector; they cannot be GCed until they are
explicitly de-registered. The callback and its closure are
pinned. If the closure references the instance, the instance is
also pinned and the garbage collector will never free the corresponding
toolkit resources. Thus a callback might want to avoid closing over
its instance, use its first parameter to reference the instance, and
have no other binding through which the instance is reachable.
The base class for all toolkit objects.
The alien address of the toolkit object. This address may be null if the object has not yet been allocated, or if it is no longer alive.
#t while gobject is alive, #f after it has been killed.
Kills gobject. Disconnects all signal callbacks and releases Scheme’s reference to the toolkit object. This procedure may be called multiple times; the reference will only be released once.
Arrange for callback to be applied to gobject and other arguments whenever gobject emits the signal with the same name as alien-function. alien-function should be a callback trampoline, as in this example:
(g-signal-connect window (C-callback "delete_event") callback)
Note that callback should reference window via parameter only. See pinned-objects.
name should be a string, e.g.:
(g-signal-disconnect window "delete_event")
The gobject-get-property and gobject-set-properties
procedures are an attempt to use GLib’s introspection facilities to
automatically determine the type of a property’s value and construct
an appropriate reflection of its value in Scheme. They have not been
tested at all.
The (default) value of gobject’s property. Property may be a string or symbol. If there is no such property, an error is signaled.
Property-list should be an even-length list of alternating names (symbols or strings) and values.
The GQuark (integer) associated with string.
The string associated with gquark (an integer). If gquark
has not been interned by gquark-from-string, an error is
signaled.
Next: Debugging Facilities, Previous: GObject, Up: API Reference
The basic interface to the GIO library is three procedures taking a
URI argument and returning either a Scheme port or a list of strings.
The URI can specify file, http and sftp protocols (and perhaps more,
depending on support in the GIO library). If an SFTP URI requires a
password, Scheme’s call-with-pass-phrase procedure is called.
If the ports are GCed or the stack unwound, pending operations are
cancelled. Re-winding the stack is an error.
These procedures do not require you to lock GLib first. They seek to acquire the lock and so cannot be used while the current thread holds the lock; it will deadlock.
Returns an input port that reads from uri.
Returns an output port that writes a new file replacing uri.
Returns a list of strings — the names of the “children” of uri, a directory resource.
A more direct interface to GIO’s GFile operations is provided by the following 8 classes and 18 operations. These procedures do require that the current thread lock GLib (see with-glib-lock).
<gfile>
make-gfile
<gfile-info>
gfile-query-info
gfile-info-list-attributes
gfile-info-get-attribute-status
gfile-info-get-attribute-value
<gfile-enumerator>
gfile-enumerate-children
gfile-enumerator-next-files
gfile-enumerator-close
<g-stream>
<g-input-stream>
g-input-stream-read
g-input-stream-skip
g-input-stream-close
<gfile-input-stream>
gfile-read
<g-output-stream>
g-output-stream-write
g-output-stream-flush
g-output-stream-close
<gfile-output-stream>
gfile-append-to
gfile-create
gfile-replace
Represents a GFile toolkit object.
Constructs a gfile for the given uri. This operation never fails, but the returned object might not support any I/O if uri is malformed or if the uri type is not supported.
Represents a GFileInfo toolkit object containing key-value
attributes (such as the type or size of a gfile).
Gets the requested information about gfile. The result is a gfile-info instance.
Attributes should be a string specifying the file attributes to
be gathered. It is not an error if it’s not possible to read a
particular requested attribute from a file — it just won’t be set.
Attributes should be a comma-separated list of attributes or
attribute wildcards. The wildcard * means all attributes, and
a wildcard like standard::* means all attributes in the
standard namespace. An example attribute query is
standard::*,owner::user.
Normally information about the target of a symlink
is returned, rather than information about the symlink itself. However
if follow-symlinks? is #f, information about the
symlink itself will be returned. If the target does not exist,
information about the symlink itself will be returned.
There are many gfile attributes. Most have boolean or integer values.
Some are enum constants. For example the standard::type
attribute’s value is a GFileType member, e.g. (C-enum
"G_FILE_TYPE_UNKNOWN"). For a complete list of GFileType members and
other GIO constants, see your gioenums.h header file.
Here are the 76 keys listed in the gfileinfo.h header:
standard::type,
standard::is-hidden,
standard::is-backup,
standard::is-symlink,
standard::is-virtual,
standard::name,
standard::display-name,
standard::edit-name,
standard::copy-name,
standard::description,
standard::icon,
standard::content-type,
standard::fast-content-type,
standard::size,
standard::allocated-size,
standard::symlink-target,
standard::target-uri,
standard::sort-order,
etag::value,
id::file,
id::filesystem,
access::can-read,
access::can-write,
access::can-execute,
access::can-delete,
access::can-trash,
access::can-rename,
mountable::can-mount,
mountable::can-unmount,
mountable::can-eject,
mountable::unix-device,
mountable::unix-device-file,
mountable::hal-udi,
mountable::can-start,
mountable::can-start-degraded,
mountable::can-stop,
mountable::start-stop-type,
mountable::can-poll,
mountable::is-media-check-automatic,
time::modified,
time::modified-usec,
time::access,
time::access-usec,
time::changed,
time::changed-usec,
time::created,
time::created-usec,
unix::device,
unix::inode,
unix::mode,
unix::nlink,
unix::uid,
unix::gid,
unix::rdev,
unix::block-size,
unix::blocks,
unix::is-mountpoint,
dos::is-archive,
dos::is-system,
owner::user,
owner::user-real,
owner::group,
thumbnail::path,
thumbnail::failed,
preview::icon,
filesystem::size,
filesystem::free,
filesystem::used,
filesystem::type,
filesystem::readonly,
filesystem::use-preview,
gvfs::backend,
selinux::context,
trash::item-count,
trash::orig-path, or
trash::deletion-date.
Lists the gfile-info attribute keys.
Namespace should be e.g. standard or *.
Returns set if the key attribute in ginfo has
been set. Returns unset if not. Returns error-setting
if there was an error collecting the value.
Returns a boolean, integer, string or list of strings depending on the value of key in ginfo.
Represents a GFileEnumerator.
Gets the requested information about the files in gfile — a directory. The result is a gfile-enumerator that produces a gfile-info for each file in the directory. If gfile is not a directory, an error is signaled.
Attributes should be a string specifying the file attributes to
be gathered. It is not an error if it’s not possible to read a
particular requested attribute from a file — it just won’t be set.
Attributes should be a comma-separated list of attributes or
attribute wildcards. The wildcard * means all attributes, and
a wildcard like standard::* means all attributes in the
standard namespace. An example attribute query is
standard::*,owner::user.
Gets up to n more gfile-infos from genum.
Closes genum.
Abstract superclass of GIO streams.
A subclass of g-stream.
Returns the number of bytes read from gstream and written into buffer.
Returns the number of bytes read from gstream and discarded.
Closes gstream.
A subclass of g-input-stream representing input from a file.
Returns a gfile-input-stream opened for reading from gfile.
A subclass of g-stream.
Returns the number of bytes written to gstream. Will return 0 only if start equals end.
Forces a write of all user-space buffered data for gstream.
Closes gstream.
A subclass of g-output-stream representing output to a file.
Returns a gfile-output-stream that overwrites gfile, possibly creating a backup copy of the file first. If the file doesn’t exist, it will be created.
This will try to replace the file in the safest way possible so that any errors during the writing will not affect an already existing copy of the file. For instance, for local files it may write to a temporary file and then atomically rename over the destination when the stream is closed.
By default files are generally created readable by everyone, but if
you include the symbol private in flags the file will be
made readable only to the current user, to the level that is supported
on the target filesystem.
Etag should be zero or false, or an alien. If etag is an
alien, it is compared to the current entity tag of the file, and if
they differ an error is signaled. This generally means that the file
has been changed since you last read it. You can get the etag for a
gfile from the etag::value attribute in
its gfile-info. You can get the gfile-info for a gfile-input-stream
with gfile-input-stream-query-info. The etag for a
gfile-output-stream is available from
gfile-output-stream-get-etag.
Backup? should be #f unless you require a backup of
an existing file to be made. If a backup cannot be made, an error
will be signaled. If you want to replace the file anyway, call
again with backup? #f.
Returns a gfile-output-stream that appends to gfile. If the file doesn’t already exist it is created.
By default files are created readable by everyone, but if you include
the symbol private in flags the file will be made
readable only to the current user, to the level that is supported on
the target filesystem.
Returns a gfile-output-stream that writes to gfile. If the file already exists an error is signaled.
By default files are created readable by everyone, but if you include
the symbol private in flags the file will be made
readable only to the current user, to the level that is supported on
the target filesystem.
Previous: GIO, Up: API Reference
If the current thread does not own GLib’s mutex, emit a warning line on stderr.
A convenient procedure to call in an emergency.
#t if Scheme’s GSource is being traced, else #f.
If trace? is #t, turns on tracing of Scheme’s GSource.
Next: GNU Free Documentation License, Previous: API Reference, Up: Top
This chapter is for the hapless debugger, or potential widget developer. It provides an overview of the mechanisms behind the scenes, like glib-thread.
The procedures implementing the API are thin wrappers, trivial convenience functions that do type checking and conversion, and hide the details of the C API. For example, a GtkLabel’s text is retrieved in two steps: a toolkit function returns an alien address, and the C string at that address is copied into the heap.
(let ((retval (make-alien '|gchar|)))
(C-call "gtk_label_get_text" retval (gobject-alien label))
(c-peek-cstring retval))
⇒ "!dlrow ,olleH"
The gtk-label-get-text wrapper procedure hides these details.
(gtk-label-get-text label) ⇒ "!dlrow ,olleH"
In the example call to gtk-label-get-text above, a Scheme
object represents the GtkLabel. It is a gtk-label instance, whose
class is a specialization of the abstract gtk-object class.
When the GLib system loads, it starts a toolkit main loop with Scheme
attached as an custom idle task. The main loop then re-starts Scheme,
which creates a thread to “run” the toolkit (actually, return to
it). Thus Scheme threads multitask with the toolkit. Scheme runs as
an idle task in the toolkit, and the toolkit runs in a Scheme thread.
A program using the GLib system does not call g_main_loop_run.
It need only create toolkit objects and attach signal handlers to
them.
Each gobject instance is tracked by the weak alist glib-cleanups,
so that the toolkit object can be g_object_unref’ed when the
instance is GCed.
The initialize-instance method for subclasses of gobject should chain
up early, adding the instance’s alien to glib-cleanups before
calling out to the toolkit. This ensures that an allocated toolkit
object will not be dropped; its alien address is on the list of GC
cleanups before it is even allocated. After the callout, the
initialize method should also g_object_ref_sink any floating
refs it receives.
The following scenarios are typical of Gtk resource management.
Temporary alien: The (alien) address of a PangoFontDescription is read from a PangoLayout member. The layout “owns” the font description. Scheme does not. The address should only be used while without-toolkit (or without-interrupts), else the toolkit may "dispose" of it while Scheme is using it.
Schemely: A toolkit object is created and reflected in Scheme by a
gobject instance. Scheme owns the toolkit object, holds a reference,
and should eventually g_object_unref it. The instance may be
shared among any number of Scheme widgets or other data structures
(e.g a file->pixbuf cache) and never explicitly “killed”.
When there are no more Scheme objects sharing the instance, it
will be GCed and its GC cleanup procedure will “kill”
(g_object_unref) the toolkit object. This may release toolkit
resources or not depending on references elsewhere in the toolkit
data structures. In any case the instance was GCed — the object
cannot be erroneously used by Scheme in the future.
Signals: The g-signal-connect procedure takes pains not to hold
a strong reference to a gobject instance. These instances can be GCed
even while signal handlers are connected. The registered callbacks
hold only a weak reference to the instance. It is assumed a callback
will not be invoked after an instance is GCed, else an error should be
signaled.
TODO: A world save hook might warn of gobject instances still on the glib-cleanups list. A world restore hook could kill them.
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Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being list their titles, with
the Front-Cover Texts being list, and with the Back-Cover Texts
being list.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.