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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/progGuideDB/language.xml | 44 |
1 files changed, 44 insertions, 0 deletions
diff --git a/docs/progGuideDB/language.xml b/docs/progGuideDB/language.xml index 3bbaba3f8..ac7aecb5b 100644 --- a/docs/progGuideDB/language.xml +++ b/docs/progGuideDB/language.xml @@ -149,6 +149,8 @@ pointcut services(Server s): target(s) && call(public * *(..)) <!-- ============================== --> +<!-- ============================== --> + <sect2 id="advice" xreflabel="advice"> <title>Advice</title> @@ -885,6 +887,48 @@ pointcut setter(Point p, int newval): target(p) && ]]></programlisting> </sect2> + + <sect2 id="pointcut-best-practice" xreflabel="pointcut-best-practice"> + <title>Writing good pointcuts</title> + + <para> + During compilation, AspectJ processes pointcuts in order to try and optimize matching performance. Examining code and determining + if each join point matches (statically or dynamically) a given pointcut is a costly process. + (A dynamic match means the match cannot be fully determined from static analysis and a test will be placed in the code + to determine if there is an actual match when the code is running). + On first encountering a pointcut declaration, AspectJ will rewrite it into an optimal form for the matching process. + What does this mean? Basically pointcuts are rewritten in DNF (Disjunctive Normal Form) and the components of the pointcut + are sorted such that those components that are cheaper to evaluate are checked first. This means users do not have to worry + about understanding the performance of various pointcut designators and may supply them in any order in their + pointcut declarations. + </para> + <para> + However, AspectJ can only work with what it is told, and for optimal performance of matching the user should think + about what they are trying to achieve and narrow the search space for matches as much as they can in the definition. + Basically there are three kinds of pointcut designator: kinded, scoping and context: + </para> + <itemizedlist> + <listitem> + Kinded designators are those which select a particular kind of join point. For example: execution, get, set, call, handler + </listitem> + <listitem> + Scoping designators are those which select a group of join points of interest (of probably many kinds). For example: within, withincode + </listitem> + <listitem> + Contextual designators are those that match (and optionally bind) based on context. For example: this, target, @annotation + </listitem> + </itemizedlist> + <para> + A well written pointcut should + try and include at least the first two types (kinded and scoping), whilst the contextual designators may be included if wishing to + match based on join point context, or bind that context for use in the advice. Supplying either just a kinded designator or + just a contextual designator will work but could affect weaving performance (time and memory used) + due to all the extra processing and analysis. + Scoping designators are very fast to match, they can very quickly dismiss groups of join points that should not be further + processed - that is why a good pointcut should always include one if possible. + </para> + + </sect2> </sect1> <!-- ============================== --> |