annotate.info: Limitations

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Limitations of the Annotation Interface

The level two annotations mechanism is known to have a number of
technical and architectural limitations.  As a consequence, in 2001,
with the release of GDB 5.1 and the addition of GDB/MI, the annotation
interface was marked as deprecated.
   This chapter discusses the known problems.

Dependant on CLI output

The annotation interface works by interspersing markups with GDB normal
command-line interpreter output.  Unfortunately, this makes the
annotation client dependant on not just the annotations, but also the
CLI output.  This is because the client is forced to assume that
specific GDB commands provide specific information.  Any change to
GDB's CLI output modifies or removes that information and,
consequently, likely breaks the client.
   Since the GDB/MI output is independant of the CLI, it does not have
this problem.

Scalability

The annotation interface relies on value annotations (*note Value
Annotations::) and the display mechanism as a way of obtaining
up-to-date value information.  These mechanisms are not scalable.
   In a graphical environment, where many values can be displayed
simultaneously, a serious performance problem occurs when the client
tries to first extract from GDB, and then re-display, all those values.
The client should instead only request and update the values that
changed.
   The GDB/MI Variable Objects provide just that mechanism.

Correctness

The annotation interface assumes that a variable's value can only be
changed when the target is running.  This assumption is not correct.  A
single assignment to a single variable can result in the entire target,
and all displayed values, needing an update.
   The GDB/MI Variable Objects include a mechanism for efficiently
reporting such changes.

Reliability

The GDB/MI interface includes a dedicated test directory
(`gdb/gdb.mi'), and any addition or fix to GDB/MI must include
testsuite changes.

Maintainability

The annotation mechanism was implemented by interspersing CLI print
statements with various annotations.  As a consequence, any CLI output
change can alter the annotation output.
   Since the GDB/MI output is independant of the CLI, and the GDB/MI is
increasingly implemented independant of the CLI code, its long term
maintenance is much easier.