libroot_build: *Actually* fix attribute usage on Haiku.

[haiku.git] / docs / user / book.dox

/*!
        \mainpage Welcome to the Haiku Book

        Below you will find documentation on the Application Programming
        Interface (API) of the Haiku operating system. This API describes
        the internals of the operating system allowing developers to write
        native C++ applications and device drivers. See the
        <a href="https://api.haiku-os.org">online version</a> for the most
        updated version of this document. If you would like to help contribute
        contact the <a href="https://www.freelists.org/list/haiku-doc">documentation
        mailing list</a>. For guidelines on how to help document the API see
        the \link apidoc Documenting the API\endlink page. A list of
        contributors can be found \ref credits page. Documenting the API is
        an ongoing process so contributions are greatly appreciated.

        The Haiku API is based on the BeOS R5 API but changes and additions have
        been included where appropriate. Important compatibility differences are
        detailed on the \ref compatibility page. New classes and methods
        and incompatible API changes to the BeOS R5 API are noted in the
        appropriate sections.

        A complete reference to the BeOS R5 API is available on the web in
        <a href="https://haiku-os.org/legacy-docs/bebook/">The Be Book</a>.
        The Be Book is used with permission from
        <a href="https://www.access-company.com/">Access Co.</a>, the current
        owners of Be's intellectual property.

        \section book_kits Kits and Servers

        The API is split into several kits and servers each detailing a different
        aspect of the operating system.
                - The \ref app is the starting point for developing applications
                        and includes classes for messaging and for interacting with
                        the rest of the system.
                - The \ref game provides classes for producing game sounds and
                        working with full screen apps.
                - The \ref interface is used to create responsive and attractive
                        graphical user interfaces building on the messaging facilities
                        provided by the Application Kit.
                        - The \link layout_intro Layout API \endlink is a new addition
                                to the Interface Kit in Haiku which provides resources to
                                layout your application flexibly and easily.
                - The \ref locale includes classes to localize your application to
                        different languages, timezones, number formatting conventions and
                        much more.
                - The \ref mail includes classes to work with e-mail files, folders,
                        protocols, and filters, as part of Haiku's unique mail handling system.
                - The \ref media provides a unified and consistent interface for media
                        streams and applications to intercommunicate.
                - The \ref midi2 describes an interface to generating, processing,
                        and playing music in MIDI format. For reference documentation on the
                        \ref midi1 is also included.
                - The \ref network handles everything network related, from interface
                        IP address settings to HTTP connections.
                - The \ref storage is a collection of classes that deal with storing and
                        retrieving information from disk.
                - The \ref support contains support classes to use in your application
                        including resources for thread safety, IO, and serialization.
                - The \ref translation provides a framework for converting data streams
                        between media formats.

        \section book_special_topics Special Topics

        - \ref drivers
        - \ref keyboard
        - \ref json
*/

///// Define main kits /////

/*!
        \defgroup app Application Kit
        \brief The Application Kit is the starting point for writing native Haiku
                GUI applications.

        The application kit is exactly what its name suggests &mdash; it is the
        basis of Haiku applications. You should first read through this document
        and the references here before moving on to the other parts of the API.

        The Application Kit classes can be divided into two groups: the messaging
        classes and the system interaction classes. The larger of the two groups is
        the messaging classes. Since the Haiku API relies on pervasive
        multithreading messaging is an essential topic for any application. Have a
        look at the \link app_messaging Introduction to Messaging \endlink for more
        information.

        The following messaging classes which allow you to easily and securely
        communicate between threads.
                - BHandler
                - BInvoker
                - BLooper
                - BMessage
                - BMessageFilter
                - BMessageQueue
                - BMessageRunner
                - BMessenger

        The second group is the system interaction classes. These classes
        provide hooks for your application to interact with the rest of the system.
        The most important class in this group is BApplication. Below is a list of
        all system interaction classes:
                - BApplication
                - BClipboard
                - BCursor
                - BPropertyInfo
                - BRoster


        \defgroup game Game Kit
        \brief The Game Kit provides classes for producing game sounds and
                working with full screen apps.


        \defgroup interface Interface Kit
        \brief API for displaying a graphical user interface.

        The Interface Kit holds all the classes you'll need to develop a GUI.
        Building on the messaging facilities provided by the Application Kit,
        the Interface Kit can be used to create a responsive and attractive
        graphical user interface.

        The most important class in the Interface Kit is the BView class, which
        handles drawing and user interaction. Pointer and keyboard events are
        processed in this class.

        Another important class is the BWindow class, which holds BViews and makes
        them visible to the user. The BWindow class also handles BView focusing
        and BMessage dispatching, among other things.

        A new addition Haiku has added over the BeOS API is the Layout API, which
        is based around the BLayoutItem and BLayout classes. These classes will
        take care of making sure all your GUI widgets end up where you want them,
        with enough space to be useful. You can start learning the Layout API
        by reading the \link layout_intro introduction \endlink.


        \defgroup locale Locale Kit
        \brief Collection of classes for localizing applications.

        \defgroup mail Mail Kit
        \brief API for working with e-mail messages and protocols.

        \defgroup media Media Kit
        \brief Collection of classes that deal with audio and video.

        \defgroup midi1 The old MIDI Kit (libmidi.so)
        \brief The old MIDI kit.


        \defgroup midi2 MIDI 2 Kit
        \brief The Midi Kit is the API that implements support for generating,
                processing, and playing music in MIDI format.

        <A HREF="https://www.midi.org/">MIDI</A>, which  stands for 'Musical
        Instrument Digital Interface', is a well-established  standard for
        representing and communicating musical data. This document serves as
        an overview. If you would like to see all the components, please look
        at \link midi2 the list with classes \endlink.

        \section book_midi2twokits A Tale of Two MIDI Kits

        BeOS comes with two different, but compatible Midi Kits. This
        documentation focuses on the "new" Midi Kit, or midi2 as we like to
        call it, that was  introduced with BeOS R5. The old kit, which we'll
        refer to as midi1, is more complete than the new kit, but less powerful.

        Both kits let you create so-called MIDI endpoints, but the endpoints
        from midi1 cannot be shared between different applications. The midi2
        kit solves that  problem, but unlike midi1 it does not include a General
        MIDI softsynth, nor does it have a facility for reading and playing
        Standard MIDI Files. Don't worry: both kits are compatible and you can
        mix-and-match them in your applications.

        The main differences between the two kits:
                - Instead of one BMidi object that both produces and consumes events,
                        we have BMidiProducer and BMidiConsumer.
                - Applications are capable of sharing MIDI producers and consumers
                        with other applications via the centralized Midi Roster.
                - Physical MIDI ports are now sharable without apps "stealing" events
                        from each other.
                - Applications can now send/receive raw MIDI byte streams (useful if
                        an application has its own MIDI parser/engine).
                - Channels are numbered 0&ndash;15, not 1&ndash;16
                - Timing is now specified in microseconds rather than milliseconds.

        \section book_midi2concepts Midi Kit Concepts

        A brief overview of the elements that comprise the Midi Kit:
                - \b Endpoints. This is what the Midi Kit is all about: sending MIDI
                        messages between endpoints. An endpoint is like a MIDI In or MIDI
                        Out socket on your equipment; it either receives information or it
                        sends information. Endpoints that send MIDI events are called
                        \b producers; the endpoints that receive those events are called
                        \b consumers. An endpoint that is created by your own application
                        is called \b local; endpoints from other applications are
                        \b remote. You can access remote endpoints using \b proxies.
                - \b Filters. A filter is an object that has a consumer and a producer
                        endpoint. It reads incoming events from its consumer, performs some
                        operation, and tells its producer to send out the results. In its
                        current form, the Midi  Kit doesn't provide any special facilities
                        for writing filters.
                - \b Midi \b Roster. The roster is the list of all published producers
                        and consumers. By publishing an endpoint, you allow other
                        applications to talk to it. You are not required to publish your
                        endpoints, in which case only your own application can use them.
                - \b Midi \b Server. The Midi Server does the behind-the-scenes work.
                        It manages the roster, it connects endpoints, it makes sure that
                        endpoints can communicate, and so on. The Midi Server is started
                        automatically when BeOS boots, and you never have to deal with it
                        directly. Just remember that it runs the show.
                - \b libmidi. The BMidi* classes live inside two shared libraries:
                        libmidi.so and libmidi2.so. If you write an application that uses
                        old Midi Kit, you must link it to libmidi.so. Applications that use
                        the new Midi Kit must link to libmidi2.so. If you want to
                        mix-and-match both kits, you should also link to both libraries.

        Here is a pretty picture:

        \image html midi2concepts.png

        \section book_midi2mediakit Midi Kit != Media Kit

        Be chose not to integrate the Midi Kit into the Media Kit as another media
        type, mainly because MIDI doesn't require any of the format negotiation that
        other media types need. Although the two kits look similar -- both have a
        "roster" for finding or registering "consumers" and "producers" -- there are
        some very important differences.

        The first and most important point to note is that BMidiConsumer and
        BMidiProducer in the Midi Kit are \b NOT directly analogous to
        BBufferConsumer and  BBufferProducer in the Media Kit! In the Media Kit,
        consumers and producers are the data consuming and producing properties
        of a media node. A filter in the Media Kit, therefore, inherits from both
        BBufferConsumer and BBufferProducer, and implements their virtual member
        functions to do its work.

        In the Midi Kit, consumers and producers act as endpoints of MIDI data
        connections, much as media_source and media_destination do in the Media Kit.
        Thus, a MIDI filter does not derive from BMidiConsumer and BMidiProducer;
        instead, it contains BMidiConsumer and BMidiProducer objects for each of its
        distinct endpoints that connect to other MIDI objects. The Midi Kit does not
        allow the use of multiple virtual inheritance, so you can't create an object
        that's both a BMidiConsumer and a BMidiProducer.

        This also contrasts with the old Midi Kit's conception of a BMidi object,
        which stood for an object that both received and sent MIDI data. In the new
        Midi Kit, the endpoints of MIDI connections are all that matters. What lies
        between the endpoints, i.e. how a MIDI filter is actually structured, is
        entirely at your discretion.

        Also, rather than use token structs like media_node to make connections
        via the MediaRoster, the new kit makes the connections directly via the
        BMidiProducer object.

        \section book_midi2remotelocal Remote vs. Local Objects

        The Midi Kit makes a distinction between remote and local MIDI objects.
        You can  only create local MIDI endpoints, which derive from either
        BMidiLocalConsumer or BMidiLocalProducer. Remote endpoints are endpoints
        that live in other applications, and you access them through BMidiRoster.

        BMidiRoster only gives you access to BMidiEndpoints, BMidiConsumers, and
        BMidiProducers. When you want to talk to remote MIDI objects, you do so
        through the proxy objects that BMidiRoster provides. Unlike
        BMidiLocalConsumer and BMidiLocalProducer, these classes do not provide a
        lot of functions. That is intentional. In order to hide the details of
        communication with MIDI endpoints in other applications, the Midi Kit must
        hide the details of how a particular endpoint is implemented.

        So what can you do with remote objects? Only what BMidiConsumer,
        BMidiProducer, and BMidiEndpoint will let you do. You can connect
        objects, get the properties of these objects -- and that's about it.

        \section book_midi2lifespan Creating and Destroying Objects

        The constructors and destructors of most midi2 classes are private,
        which means that you cannot directly create them using the C++
        <CODE>new</CODE> operator, on the  stack, or as globals. Nor can you
        <CODE>delete</CODE> them. Instead, these objects are obtained through
        BMidiRoster. The only two exceptions to this rule are BMidiLocalConsumer
        and BMidiLocalProducer. These two objects may be directly created and
        subclassed by developers.

        \section book_midi2refcount Reference Counting

        Each MIDI endpoint has a reference count associated with it, so that
        the Midi Roster can do proper bookkeeping. When you construct a
        BMidiLocalProducer or  BMidiLocalConsumer endpoint, it starts with a
        reference count of 1. In addition, BMidiRoster increments the reference
        count of any object it hands to you as a result of
        \link BMidiRoster::NextEndpoint() NextEndpoint() \endlink or
        \link BMidiRoster::FindEndpoint() FindEndpoint() \endlink.
        Once the count hits  0, the endpoint will be deleted.

        This means that, to delete an endpoint, you don't call the
        <CODE>delete</CODE>  operator directly; instead, you call
        \link BMidiEndpoint::Release() Release() \endlink.
        To balance this call, there's also an
        \link BMidiEndpoint::Acquire() Acquire() \endlink, in case you have two
        disparate parts of your application working with the endpoint, and you
        don't want to have to keep track of who needs to Release() the endpoint.

        When you're done with any endpoint object, you must Release() it.
        This is true  for both local and remote objects. Repeat after me:
        Release() when you're done.

        \section book_midi2events MIDI Events

        To make some actual music, you need to
        \link BMidiProducer::Connect() Connect() \endlink your consumers to
        your producers. Then you tell the producer to "spray" MIDI events to all
        the connected consumers. The consumers are notified of these incoming
        events through a set of hook functions.

        The Midi Kit already provides a set of commonly used spray functions,
        such as  \link BMidiLocalProducer::SprayNoteOn() SprayNoteOn() \endlink,
        \link BMidiLocalProducer::SprayControlChange() SprayControlChange()
        \endlink, and so on. These correspond one-to-one with the message types
        from the MIDI spec. You don't need to be a MIDI expert to use the kit, but
        of course some knowledge of the protocol helps. If you are really hardcore,
        you can also use the
        \link BMidiLocalProducer::SprayData() SprayData() \endlink to send raw MIDI
        events to the consumers.

        At the consumer side, a dedicated thread invokes a hook function for every
        incoming MIDI event. For every spray function, there is a corresponding hook
        function, e.g. \link BMidiLocalConsumer::NoteOn() NoteOn() \endlink and
        \link  BMidiLocalConsumer::ControlChange() ControlChange() \endlink.
        The hardcore MIDI fanatics among you will be pleased to know that you can
        also tap into the \link BMidiLocalConsumer::Data() Data() \endlink hook and
        get your hands dirty with the raw MIDI data.

        \section book_midi2time Time

        The spray and hook functions accept a bigtime_t parameter named "time". This
        indicates when the MIDI event should be performed. The time is given in
        microseconds since the computer booted. To get the current tick measurement,
        you call the system_time() function from the Kernel Kit.

        If you override a hook function in one of your consumer objects, it should
        look  at the time argument, wait until the designated time, and then perform
        its action. The preferred method is to use the Kernel Kit's
        <CODE>snooze_until()</CODE> function, which sends the consumer thread to
        sleep  until the requested time has come. (Or, if the time has already
        passed, returns immediately.)

        Like this:

        \code
void MyConsumer::NoteOn(
    uchar channel, uchar note, uchar velocity, bigtime_t time)
{
    snooze_until(time, B_SYSTEM_TIMEBASE);
    ...do your thing...
}
        \endcode

        If you want your producers to run in real time, i.e. they produce MIDI data
        that needs to be performed immediately, you should pass time 0 to the spray
        functions (which also happens to be the default value). Since time 0 has
        already passed, <CODE>snooze_until()</CODE> returns immediately, and the
        consumer will process the events as soon as they are received.

        To schedule MIDI events for a performance time that lies somewhere in the
        future, the producer must take into account the consumer's latency.
        Producers  should attempt to get notes to the consumer by or before
        <I>(scheduled_performance_time - latency)</I>. The time argument is still
        the scheduled performance time, so if your consumer has latency, it should
        snooze like this before it starts to perform the events:

        \code
snooze_until(time - Latency(), B_SYSTEM_TIMEBASE);
        \endcode

        Note that a typical producer sends out its events as soon as it can;
        unlike a consumer, it does not have to snooze.

        \section book_midi2ports Other Timing Issues

        Each consumer object uses a Kernel Kit port to receive MIDI events from
        connected producers. The queue for this port is only 1 message deep.
        This means that if the consumer thread is asleep in a
        <CODE>snooze_until()</CODE>, it will not read its port. Consequently,
        any producer that tries to write a new event to this port will block until
        the consumer thread is ready to receive a new message. This is intentional,
        because it prevents producers from generating and queueing up thousands of
        events.

        This mechanism, while simple, puts on the producer the responsibility
        for sorting the events in time. Suppose your producer sends three Note
        On events, the first on t + 0, the second on t + 4, and the third on t + 2.
        This last event won't be received until after t + 4, so it will be two ticks
        too late. If this sort of thing can happen with your producer, you should
        somehow sort the events before you spray them. Of course, if you have two or
        more producers connected to the same consumer, it is nearly impossible to
        sort this all out (pardon the pun). So it is not wise to send the same kinds
        of events from more than one producer to one consumer at the same time.

        The article Introduction to MIDI, Part 2 in <A
        HREF="https://open-beos.sourceforge.net/nsl.php?mode=display&id=36">OpenBeOS
        Newsletter 36</A> describes this problem in more detail, and provides a
        solution. Go read it now!

        \section book_midi2filters Writing a Filter

        A typical filter contains a consumer and a producer endpoint. It receives
        events from the consumer, processes them, and sends them out again using the
        producer. The consumer endpoint is a subclass of BMidiLocalConsumer, whereas
        the producer is simply a BMidiLocalProducer, not a subclass. This is a
        common  configuration, because consumers work by overriding the event hooks
        to do work  when MIDI data arrives. Producers work by sending an event when
        you call their  member functions. You should hardly ever need to derive from
        BMidiLocalProducer (unless you need to know when the producer gets connected
        or disconnected, perhaps), but you'll always have to override one or more of
        BMidiLocalConsumer's member functions to do something useful with incoming
        data.

        Filters should ignore the time argument from the spray and hook functions,
        and  simply pass it on unchanged. Objects that only filter data should
        process the  event as quickly as possible and be done with it. Do not
        <CODE>snooze_until()</CODE> in the consumer endpoint of a filter!

        \section book_midi2apidiffs API Differences

        As far as the end user is concerned, the Haiku Midi Kit is mostly the same
        as the BeOS R5 kits, although there are a few small differences in the API
        (mostly bug fixes):
                - BMidiEndpoint::IsPersistent() always returns false.
                - The B_MIDI_CHANGE_LATENCY notification is now properly sent. The Be
                        kit  incorrectly set be:op to B_MIDI_CHANGED_NAME, even though the
                        rest of the  message was properly structured.
                - If creating a local endpoint fails, you can still Release() the object
                  without crashing into the debugger.

        \section book_midi2seealso See also

        More about the Midi Kit:
                - \ref Midi2Defs.h
                - Be Newsletter Volume 3, Issue 47 - Motor Mix sample code
                - Be Newsletter Volume 4, Issue 3 - Overview of the new kit
                - <A HREF="https://haiku-os.org/documents/dev/introduction_to_midi_part_1">Newsletter
                  33</A>, Introduction to MIDI, Part 1
                - <A HREF="https://haiku-os.org/documents/dev/introduction_to_midi_part_2">Newsletter
                  36</A>, Introduction to MIDI, Part 2
                - Sample code and other goodies at the
                  <A HREF="https://haiku-os.org/about/teams/midi_kit">Haiku Midi Kit team page</A>

        Information about MIDI in general:
                - <A HREF="https://www.midi.org">MIDI Manufacturers Association</A>
                - <A HREF="https://www.borg.com/~jglatt/tutr/miditutr.htm">MIDI Tutorials</A>
                - <A HREF="https://www.borg.com/~jglatt/tech/midispec.htm">MIDI Specification</A>
                - <A HREF="https://www.borg.com/~jglatt/tech/midifile.htm">Standard MIDI File Format</A>
                - <A HREF="https://www.io.com/~jimm/midi_ref.html">Jim Menard's MIDI Reference</A>


        \defgroup network Network Kit
        \brief Classes that deal with all network connections and communications.

        The Haiku Network Kit consists of:
        - A modular, add-ons based network stack
        - Two shared libraries, libnetwork.so and libnetapi.so
        - A stack driver, acting as interface between the network stack and
          libnetwork.so
        - Basic network apps
        - A modular GUI preflet

        The libnet.so shared library is the way that BeOS R5 provided POSIX/BSD
        API sockets to apps. Being binary compatible with BeOS R5 has made this
        library implementation tedious. To counter this, the libnetapi.so shared
        library was developed. It contains thin C++ classes wrapping the C
        sockets POSIX/BSD API into these BNet* classes we're used under BeOS.

        The stack driver is the interface between libnet.so and the real stack
        behind it, hosted by the network stack kernel modules. Its purposes
        include:
        -# Providing sockets to file descriptors translation support
        -# Providing support for select() on sockets
        -# Loading the network stack on first access, and then keeping it for
           further accesses

        The following diagram illustrates the network stack design on Haiku:

        \image html obos_net_stack_design_1.gif

        The Network Kit includes a handful of useful networking related apps
        including ping, ifconfig, route, traceroute, and arp.

        See the User Guide for more information about the
        <a href="https://haiku-os.org/docs/userguide/en/preferences/network.html">Network preferences app</a>
        included as part of the Network Kit.


        \defgroup storage Storage Kit
        \brief Collection of classes that deal with storing and retrieving
                information from disk.


        \defgroup support Support Kit
        \brief Collection of utility classes that are used throughout the API.

        The Support Kit provides a handy set of classes that you can use in your
        applications. These classes provide:
                - \b Thread \b Safety. Haiku can execute multiple threads of an
                        application in parallel, letting certain parts of an application
                        continue when one part is stalled, as well as letting an application
                        process multiple pieces of data at the same time on multicore or
                        multiprocessor systems. However, there are times when multiple
                        threads desire to work on the same piece of data at the same time,
                        potentially causing a conflict where variables or pointers are
                        changed by one thread causing another to execute incorrectly. To
                        prevent this, Haiku implements a \"locking\" mechanism, allowing one
                        thread to \"lock out\" other threads from executing code that might
                        modify the same data.
                  - \b Archiving \b and \b IO. These classes allow a programmer to
                        convert objects into a form that can more easily be transferred to
                        other applications or stored to disk, as well as performing basic
                        input and output operations.
                  - \b Memory \b Allocation. This class allows a programmer to hand off
                        some of the duties of memory accounting and management.
                  - \b Common \b Datatypes. To avoid unnecessary duplication of code
                        and to make life easier for programmers, Haiku includes classes that
                        handle management of ordered lists and strings.

        There are also a number of utility functions to time actions, play system
        alert sounds, compare strings, and atomically manipulate integers. Have a
        look at the overview, or go straight to the complete
        \link support list of components \endlink of this kit.

        \section book_overview Overview
                - Thread Safety:
                        - BLocker provides a semaphore-like locking mechanism allowing for
                                recursive locks.
                        - BAutolock provides a simple method of automatically removing a
                                lock when a function ends.
                        - \ref TLS.h "Thread Local Storage" allows a global variable\'s
                                content to be sensitive to thread context.
                - Archiving and IO:
                        - BArchivable provides an interface for \"archiving\" objects so
                                that they may be sent to other applications where an identical
                                copy will be recreated.
                        - BArchiver simplifies archiving of BArchivable hierarchies.
                        - BUnarchiver simplifies unarchiving hierarchies that have been
                                archived using BArchiver.
                        - BFlattenable provides an interface for \"flattening\" objects so
                                that they may be easily stored to disk.
                - BDataIO provides an interface for generalized read/write streams.
                        - BPositionIO extends BDataIO to allow seeking within the data.
                        - BBufferIO creates a buffer and attaches it to a BPositionIO
                                stream, allowing for reduced load on the underlying stream.
                        - BMemoryIO allows operation on an already-existing buffer.
                        - BMallocIO creates and allows operation on a buffer.
                - Memory Allocation:
                        - BBlockCache allows an application to allocate a \"pool\" of
                                memory blocks that the application can fetch and dispose of as
                                it pleases, letting the application make only a few large memory
                                allocations, instead of many small expensive allocations.
                - Common Datatypes:
                        - BList allows simple ordered lists and provides common access,
                                modification, and comparison functions.
                        - BString allows strings and provides common access, modification,
                                and comparison functions.
                - BStopWatch allows an application to measure the time an action takes.
                        - \ref support_globals "Global functions"
                        - \ref TypeConstants.h "Common types and constants"
                        - Error codes for all kits


        \defgroup translation Translation Kit
        \brief Provides a framework for converting data streams between media
                formats.


        \defgroup libtranslation (libtranslation.so)

        \defgroup libbe (libbe.so)


        \defgroup libroot (libroot.so)
*/

///// Subgroups /////

/*!
        \defgroup support_globals Global functions
        \ingroup support

        \defgroup layout Layout API
        \brief Provides classes for automatically laying out UIs.
        \ingroup interface
*/


///// Special Topics /////

/*!
        \defgroup drivers Device Drivers

        \defgroup json Json Handling
        \brief Provides for parsing and writing of data in Json encoding.
*/