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| <title>GDB’s Obsolete Annotations: Limitations</title> |
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| <a name="Limitations"></a> |
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| Next: <a href="Migrating-to-GDB_002fMI.html#Migrating-to-GDB_002fMI" accesskey="n" rel="next">Migrating to GDB/MI</a>, Previous: <a href="Annotations-Overview.html#Annotations-Overview" accesskey="p" rel="prev">Annotations Overview</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> |
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| <a name="Limitations-of-the-Annotation-Interface"></a> |
| <h2 class="chapter">2 Limitations of the Annotation Interface</h2> |
| |
| <p>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 <small>GDB</small> 5.1 and the addition of <small>GDB/MI</small>, |
| the annotation interface was marked as deprecated. |
| </p> |
| <p>This chapter discusses the known problems. |
| </p> |
| <a name="Dependant-on-CLI-output"></a> |
| <h3 class="section">2.1 Dependant on <small>CLI</small> output</h3> |
| |
| <p>The annotation interface works by interspersing markups with |
| <small>GDB</small> normal command-line interpreter output. Unfortunately, this |
| makes the annotation client dependant on not just the annotations, but |
| also the <small>CLI</small> output. This is because the client is forced to |
| assume that specific <small>GDB</small> commands provide specific information. |
| Any change to <small>GDB</small>’s <small>CLI</small> output modifies or removes that |
| information and, consequently, likely breaks the client. |
| </p> |
| <p>Since the <small>GDB/MI</small> output is independent of the <small>CLI</small>, it does not |
| have this problem. |
| </p> |
| <a name="Scalability"></a> |
| <h3 class="section">2.2 Scalability</h3> |
| |
| <p>The annotation interface relies on value annotations (see <a href="Value-Annotations.html#Value-Annotations">Value Annotations</a>) and the display mechanism as a way of obtaining up-to-date |
| value information. These mechanisms are not scalable. |
| </p> |
| <p>In a graphical environment, where many values can be displayed |
| simultaneously, a serious performance problem occurs when the client |
| tries to first extract from <small>GDB</small>, and then re-display, all those |
| values. The client should instead only request and update the values |
| that changed. |
| </p> |
| <p>The <small>GDB/MI</small> Variable Objects provide just that mechanism. |
| </p> |
| <a name="Correctness"></a> |
| <h3 class="section">2.3 Correctness</h3> |
| |
| <p>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. |
| </p> |
| <p>The <small>GDB/MI</small> Variable Objects include a mechanism for efficiently |
| reporting such changes. |
| </p> |
| <a name="Reliability"></a> |
| <h3 class="section">2.4 Reliability</h3> |
| |
| <p>The <small>GDB/MI</small> interface includes a dedicated test directory |
| (<samp>gdb/gdb.mi</samp>), and any addition or fix to <small>GDB/MI</small> must include |
| testsuite changes. |
| </p> |
| <a name="Maintainability"></a> |
| <h3 class="section">2.5 Maintainability</h3> |
| |
| <p>The annotation mechanism was implemented by interspersing <small>CLI</small> print |
| statements with various annotations. As a consequence, any <small>CLI</small> |
| output change can alter the annotation output. |
| </p> |
| <p>Since the <small>GDB/MI</small> output is independent of the <small>CLI</small>, and the |
| <small>GDB/MI</small> is increasingly implemented independent of the <small>CLI</small> |
| code, its long term maintenance is much easier. |
| </p> |
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| Next: <a href="Migrating-to-GDB_002fMI.html#Migrating-to-GDB_002fMI" accesskey="n" rel="next">Migrating to GDB/MI</a>, Previous: <a href="Annotations-Overview.html#Annotations-Overview" accesskey="p" rel="prev">Annotations Overview</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p> |
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