5. libgdb

5.1 libgdb 1.0

5.2 libgdb 2.0

Since libgdb development is on-going, its architecture is still evolving. The following components have so far been identified:

• Observer - `gdb-events.h'.
• Builder - `ui-out.h'
• Event Loop - `event-loop.h'
• Library - `gdb.h'

The model that ties these components together is described below.

5.3 The libgdb Model

A client of libgdb interacts with the library in two ways.

• As an observer (using `gdb-events') receiving notifications from libgdb of any internal state changes (break point changes, run state, etc).
• As a client querying libgdb (using the `ui-out' builder) to obtain various status values from GDB.

Since libgdb could have multiple clients (e.g. a GUI supporting the existing GDB CLI), those clients must co-operate when controlling libgdb. In particular, a client must ensure that libgdb is idle (i.e. no other client is using libgdb) before responding to a `gdb-event' by making a query.

5.4 CLI support

At present GDB's CLI is very much entangled in with the core of libgdb. Consequently, a client wishing to include the CLI in their interface needs to carefully co-ordinate its own and the CLI's requirements.

It is suggested that the client set libgdb up to be bi-modal (alternate between CLI and client query modes). The notes below sketch out the theory:

• The client registers itself as an observer of libgdb.
• The client create and install cli-out builder using its own versions of the ui-file gdb_stderr, gdb_stdtarg and gdb_stdout streams.
• The client creates a separate custom ui-out builder that is only used while making direct queries to libgdb.

When the client receives input intended for the CLI, it simply passes it along. Since the cli-out builder is installed by default, all the CLI output in response to that command is routed (pronounced rooted) through to the client controlled gdb_stdout et. al. streams. At the same time, the client is kept abreast of internal changes by virtue of being a libgdb observer.

The only restriction on the client is that it must wait until libgdb becomes idle before initiating any queries (using the client's custom builder).

5.5 libgdb components

Observer - `gdb-events.h'

Builder - `ui-out.h'

Event Loop - `event-loop.h'

The event-loop will eventually be made re-entrant. This is so that can better handle the problem of some commands blocking instead of returning.

Library - `gdb.h'