Glossary

Term	Definition	Chapter
active object	Responsible for issuing requests to	8, 9
	asynchronous service providers and
	handling those requests on completion.
	Derives from CActive.
active scheduler	Responsible for scheduling events to the	8, 9
	active objects in an event-handling program.
asynchronous	A system, component or class, which	8, 9
service provider	provides a service asynchronously, typically
	to an active object. Asynchronous requests
	are indicated by function calls with a
	TRequestStatus reference parameter.
backward	Updating a component in such a way that	18
compatibility	client code which used the original version
	can continue to work with the updated
	version. See also forward compatibility.
binary	Modifying a library in such a way that code	18
compatibility	which linked against the previous version
	can continue to run with the new version
	without needing recompilation.
C function	In the context of Symbian OS, this refers to a	3
	function with a trailing C in its name, e.g.

NewLC(). If successful, this type of function leaves one or more objects on the cleanup stack when it returns.

340	GLOSSARY
Term	Definition	Chapter
chunk	A unit of memory allocation, where a linear	13
	region of RAM is mapped into contiguous
	logical addresses.
clanger	The Clangers are a race of highly-civilized,	throughout
	small, bright pink, long-nosed,
	mouse-shaped persons who stand upright
	on big flappy feet (see www.clangers.co.uk
	for more information).
cleanup stack	Takes responsibility for cleaning up the	3
	objects pushed onto it if a leave
	occurs.
client interface	A member function in a client-side session	11, 12
function	(or subsession) class that sends a specific
	message request to a server, identified by an
	opcode.
context switch	A switch in execution between one thread	10, 11, 12
	or process and another. This involves saving
	the context of the currently executing thread
	or process (i.e. its address space mappings)
	and restoring the context of the newly
	executing thread or process.
descriptor	A string, so-called because it is	4, 5
	self-describing. All descriptor classes derive
	from TDesC, which describes an area of
	memory used as either a string or binary
	data.
descriptorize	To marshal a flat data object, typically a	6, 11, 12
	struct or T class, into a descriptor for
	inter-thread data transfer.
DLL (dynamic	Dynamic link libraries contain functions	13
link library)	that are linked and stored separately from
	the programs that use them.
DLL export table	An area in the DLL which lists the DLL	13
	addresses of exported items. On Symbian
	OS, these items are indexed by
	ordinal.
E32	Collective term for the base components of
	Symbian OS.
ECOM	A generic framework in Symbian OS from	14
	v7.0 for use with plug-in modules.

	GLOSSARY	341
Term	Definition	Chapter
emulator	An implementation of Symbian OS hosted	13
	on a PC running Microsoft Windows.
	Compare with target hardware.
entry point	A function called when a DLL is loaded or	13
	attached by a thread or process. In Symbian
	OS, the function E32Dll() is usually
	coded as the entry point.
EPOC, EPOC32	Earlier names for Symbian OS. Rumors that
	this stood for ‘Electronic Piece of Cheese’
	are unconfirmed.
exec call	A call to the kernel via a software interrupt	10
	(see this useful paper by John Pagonis for
	more details www.symbian.com/developer/
	techlib/papers/userland/userland.pdf)
F32	Collective term for the components making
	up the Symbian OS file server.
FEP (Front-End	Allows the input of characters by a user, for	13
Processor)	example, by handwriting recognition or
	voice, and converts the input transparently
	into text.
file server	The server thread that mediates all file	11
	system operations. All application programs
	that use files are clients of this thread.
flat buffer	A dynamic buffer using flat storage, i.e. a	7
	single segment of memory (see also
	segmented buffer).
forward	Updating a component in such a way that	18
compatibility	code which works with the new version also
	works with the original version. See also
	backward compatibility.
framework	A component that allows its functionality to	13, 14
	be extended by plug-in modules, sometimes
	known as framework extensions. The
	framework loads the extensions as required
	at runtime.
framework	Provides plug-in functionality to a	14
extension	framework, typically by implementing
	interfaces defined by that framework. On
	Symbian OS, a framework extension is
	implemented as a polymorphic DLL.

342

GLOSSARY

Term

freeze

import library (.lib)

IPC (Inter-Process Communication)

just-in-time (JIT)

kernel

L function

leave

mixin

module definition file (.def)

null thread

Definition	Chapter
The process of fixing the association	13
between name and ordinal, for functions
exported from a DLL. It is a colloquial
reference to a .def file (see module
definition file).
A static library that an application program	13
uses at link time to resolve references to
symbols defined in a corresponding DLL.
Information from this library concerning the
location of export functions in the DLL is
included in the application’s executable
file.
Used by clients to communicate with	11, 12
out-of-process servers on Symbian OS.
Just-in-time debugging is used to attach a	15
debugger to a process at the point at which
it is about to terminate.
The core of the operating system. It manages	10
memory, loads processes and libraries and
schedules threads for execution.
A function with a trailing L in its name, e.g.	2
NewL(), which indicates that it may leave.
Symbian OS exception handling. A function	2
leaves when User::Leave()is called. It
causes a return to the current trap harness.
An interface class for ”mixing in” with	1
primary base classes, and the only form of
multiple inheritance encouraged on
Symbian OS.
A file that specifies an ordinal value for each	13, 18
named function or data item to be exported
from a DLL. It is used to insert ordinal
information into the DLL export table,
allowing exports to be accessed by ordinal
from clients of the DLL.
The lowest-priority thread in the system,	10
belonging to the kernel. It only runs when
there is no higher priority thread to run and
usually puts the phone into power-saving
mode.

	GLOSSARY	343
Term	Definition	Chapter
OOM	An error caused when the available RAM	throughout
(out-of-memory)	has been exhausted, preventing further heap
	allocation.
panic	A run-time exception on Symbian OS that	15, 16
	terminates the current thread. Panics tend to
	be caused when assertion statements
	fail.
plug-in	A polymorphic interface DLL used to extend	13, 14
	a framework application.
polymorphic	A DLL that provides plug-in functionality to	13, 14
DLL	another program by implementing a defined
	interface. These are typically known as
	plug-ins and are loaded dynamically by
	another program (usually a framework)
	using RLibrary::Load(). Compare with
	shared library.
process	The unit of memory protection on Symbian	10
	OS. One user process may not access
	another’s memory. A process may contain
	one or more threads.
recognizer	A plug-in that examines data from a file and	13
	returns its data (MIME) type, if recognized.
request	A semaphore associated with a thread,	8, 9
semaphore	which is used to indicate the completion of
	an asynchronous request.
request status	An object that indicates the completion	8, 9
	status of a request, represented by
	TRequestStatus.
ROM	Read-Only Memory. This is permanent	13
	memory that can be read but not (easily)
	written to. It holds code and data that must
	persist when the phone is switched off. On
	Symbian OS, it is usually identified as the Z:
	drive.
SDK	Software Development Kit.
segmented	A dynamic buffer using segmented storage,	7
buffer	which consists of a doubly-linked list of
	segments. Segments are added when the
	buffer needs to expand and removed when
	it is compressed. See also flat buffer.

344	GLOSSARY
Term	Definition	Chapter
server call	A call to the kernel in which the kernel	11, 12
	server thread runs on behalf of the user
	program. See this useful paper by John
	Pagonis for more information
	www.symbian.com/developer/techlib/
	papers/userland/userland.pdf
session	The channel of communication between a	11, 12
	client and a server.
shared library	A library that is loaded by the DLL loader	13
	when an executable that links to it is
	loaded. Compare with polymorphic
	DLL.
static library	Other executable code may link to this	13
	library to resolve references to exported
	functions. Builds with a .lib
	extension.
target hardware	A phone handset running Symbian OS	10, 13
	(compare with emulator)
thin template	An idiom used to minimize code bloat from	19
	the use of standard C++ templates.
thread-local	A machine word of memory that may be	13
storage (TLS)	used to anchor information in the context of
	a DLL or a thread. Used instead of writable
	static data, which is not supported for
	Symbian OS DLLs.
TRAP, TRAPD	Trap harness macros within which	2
	leaving code may be executed and any
	leaves ”caught”. Can be likened to a
	combination of try and catch in standard
	C++.
two-phase	An idiom used on Symbian OS to ensure	4
construction	that an object can be initialized safely using
	leaving code.
UID (unique	A unique 32-bit number used in a	13
identifier)	compound identifier to identify an object,
	file type, etc. When users refer to ”UID”
	they often mean UID3, the identifier for a
	particular program.
UID type	A set of three UIDs that, in combination,	13
	identify a Symbian OS object.

	GLOSSARY	345
Term	Definition	Chapter
UID1	The first UID in a compound identifier (UID	13
	type). It identifies the general type of a
	Symbian OS object and can be thought of as
	a system-level identifier; for example
	executables, DLLs and file stores are all
	distinguished by UID1.
UID2	The second UID in a compound identifier	13
	(UID type). It is used to distinguish within a
	type (e.g. between types of DLL) and can be
	thought of as an interface identifier. For
	example, static interface and polymorphic
	interface DLLs are distinguished by UID2.
UID3	The third UID in a compound identifier	13
	(UID type). It identifies a particular subtype
	and can be thought of as a project identifier
	(for example, UID3 may be shared by all
	objects belonging to a given program,
	including library DLLs, framework DLLs,
	and all documents).
Unicode	A 16-bit character set that is used to assign	5, 6
	unique character codes for a wide range of
	languages.