select() system call. The
select() system call is a function that scans a set of BSD like socket descriptors and
returns when one or more sockets are ready for either network read or
write. Asynchronous I/O is based on signals instead of a select() call. Each
time a socket is ready for a network operation, for example read, a signal is generated. This
signal can then be caught by the application in an signal handler. Using the select()
call is called reactive whereas using signals is called pro-active.
The W3C Reference Library supports both approaches under Windows, and therefore you must choose
which model you prefer. The choice can depend on what type of application you are using and what
other libraries you are using.
Interleaved I/O Using select()
In this mode the Event Manager registers all
active sockets and passes them to a select() call which then processes the registered
sockets. When select() returns the Event Manager dispatches the appropriate handlers as
the sockets get ready.
What to do: This is the default mode and you don't have to do anything
Asynchronous I/O based using Signals
Here the Event Manager registers all active sockets
using WSAAsyncSelect which is part of the WinSock API. When AsyncSelect()
which is the asynchronous equivalent to the select() returns, the Event Manager
dispatches the results of the AsyncSelect().
What to do: Define WWW_WIN_ASYNC as a preprocessor directive when generating the
project for the Library.
Console vs Windows Application
A Windows application can use either a character based command line interface, or a graphic windows
interface. Many MS-DOS applications do run as a simple command line tool which doesn't use GUI at
all. Under Win32, there is a notion of a console application. This means that
all user interaction happens through a standard DOS shell interface, with a FILE pointer like that
in Unix. This does not exist under Win16, where a Windows window is required.
The Library supports both the console and the windows interface, and again you must choose what
version you prefer. This is often something you have to decide as you are creating the project.
Windows Application
If you want to make a windows application then this is the mode to use. Eric Prud'hommeaux has
provided a Windows application wrapper for the W3C Line Mode
Browser which you can use in order to build the browser as a Windows application. This is found
in www.c. Three other modules, scroll.c and lib.c provide the window for the
application.
What to do: This is the default mode and you don't
have to do anything
Console Application
The console option is available only in Win32 in which case all user interaction happens through the
Win32 console window. This model strongly resembles a Unix vt100 terminal interface.
What to do: Define _CONSOLE as preprocessor
directives when generating the project for the Library.
Static vs Dynamic Libraries
Windows has a concept of both static and dynamic libraries, the latter also known as
DLLs. It is out of scope here to describe the difference between DLLs and static libraries,
but as DLLs is based on a lot more flexible memory model it is almost always the best solution for
Windows applications.
The W3C Reference Library support both models in that if can be built as either one big static
library or as a set of small DLLs. As mentioned, it is in almost all cases recommended to build DLLs
instead of static libraries, and on Win16 it is required because a static library is too big.
Static Library
The libraries may be build as one large static library. This is how libwww is implemented on Unix
platforms. Subsequent references to the various DLLs may all be assumed to refer to the staticly
linked libwww. Care has been taken to insure that there are no #define conflicts where one
library would want a #define that would interfere with the modules in other libraries. When
building a static library, see the following sections on Select Options and Input/Output Options, accumulate all the #defines that are required, and build
the whole libwww with those #defines.
What to do: This is the default mode and you don't
have to do anything but please note, that it is not recommended to staticly link to the libraries if
you are building a Win16 application as it creates segment size problems.
Dynamic Libraries (DLLs)
The libwww can also be built as a set of DLLs that follows the modular architecture of the
Library. This enables the application programmer to choose exactly what functionality should be
enabled in the application. The boundaries between these DLLs are based on module interdependency
and some assumptions regarding which modules may be replaced by the application. Unlike static
linking, dynamic linking requires that all the modules in a DLL be replaced at once. This is because
the DLL needs all internal references to be resolved at build time.
What to do: Define WWW_WIN_DLL as
preprocessor directives when generating the project for the Library.
windll.dll and contains also the
definition of the global trace flag definition.
What to do: Include the windll.dll as a part of
your project and make sure that it is built as the first DLL.
What to do: Generate the DLLs according to the def
files so the exported interface is identical to the set of functions defined in the actual c files
included in the DLL.