--- /dev/null
+<part id='dependency-resolution'>
+<title>Dependency Resolution</title>
+&dependency_resolution_package_modeling;
+&dependency_resolution_decision_making;
+&dependency_resolution_task_scheduling;
+</part>
--- /dev/null
+<chapter id='dependency-resolution-decision-making'>
+<title>Decision Making</title>
+<sect1 id='dependency-resolution-decision-making-dependency-expression-evaluation'>
+ <title>Dependency Expression Evaluation</title>
+ <para>
+ In terms of boolean logic, a dependency expression can
+ be expressed in disjunctive normal form (DNF), which is
+ a disjunction of conjunctive clauses. Each conjunctive clause
+ represents one possible alternative combination of dependency
+ atoms capable of satisfying the dependency expression.
+ </para>
+</sect1>
+<sect1 id='dependency-resolution-decision-making-look-ahead'>
+ <title>Look-Ahead</title>
+ <para>
+ When there are multiple combinations to choose from,
+ a look-ahead mechanism will choose an optimal combination
+ to satisfy constraints and minimize cost. The
+ following package states influence the cost calculation for
+ a given combination:
+ <itemizedlist>
+ <listitem>
+ installed
+ </listitem>
+ <listitem>
+ selected (for installation)
+ </listitem>
+ <listitem>
+ not selected (for installation)
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ In cost calculations, virtual packages by themselves are
+ considered to cost nothing since they do not directly install anything.
+ It is the dependencies of a virtual package that contribute to it's cost.
+ </para>
+ <sect2 id='dependency-resolution-decision-making-look-ahead-constraint-propagation'>
+ <title>Constraint Propagation</title>
+ <para>
+ Combinations that include packages from the "installed" or
+ "selected" categories are less costly than those that
+ include packages from the "not selected" category.
+ When a package is chosen for installation, it transitions to the
+ "selected" state. This state change propagates
+ to the cost calculations of later decisions,
+ influencing later decisions to be consistent with earlier decisions.
+ This feedback mechanism serves to propagate constraints and can
+ influence the modeling process to
+ converge on a more optimal final state.
+ </para>
+ </sect2>
+ <sect2 id='dependency-resolution-decision-making-look-ahead-expanded-search-space'>
+ <title>Expanded Search Space</title>
+ <para>
+ When evaluating virtual atoms, an expanded search space is
+ considered which recursively traverses
+ the dependencies of virtual packages
+ from all slots matching a given virtual atom. All combinations in
+ this expanded search space are considered when choosing an optimal
+ combination to satisfy constraints with minimal cost.
+ </para>
+ </sect2>
+</sect1>
+</chapter>
--- /dev/null
+<chapter id='dependency-resolution-package-modeling'>
+<title>Package Modeling</title>
+
+<sect1 id='dependency-resolution-package-modeling-constraint-satisfaction'>
+ <title>Constraint Satisfaction</title>
+ <sect2 id='dedependency-resolution-package-modeling-constraint-satisfaction-constraint-types'>
+ <title>Constraint Types</title>
+ <para>
+ Dependency resolution involves satisfaction of
+ many constraints:
+ <itemizedlist>
+ <listitem>
+ Persistent configuration parameters, like those that come from
+ make.profile, make.conf, and the /etc/portage directory.
+ </listitem>
+ <listitem>
+ Current command parameters, which may include options, atoms, or sets.
+ </listitem>
+ <listitem>
+ <link linkend='dependency-resolution-package-modeling-constraint-satisfaction-package-dependencies'>
+ Package Dependencies</link>
+ </listitem>
+ </itemizedlist>
+ </para>
+ </sect2>
+
+ <sect2 id='dependency-resolution-package-modeling-constraint-satisfaction-package-dependencies'>
+ <title>Package Dependencies</title>
+ <para>
+ Common types of package dependencies:
+ <itemizedlist>
+ <listitem>
+ Files required for building or installing. Downloads may
+ be necessary to satisfy these.
+ </listitem>
+ <listitem>
+ Other packages required to be installed for
+ buildtime or runtime.
+ </listitem>
+ <listitem>
+ Blockers that prevent conflicting packages from being installed
+ simultaneously.
+ </listitem>
+ </itemizedlist>
+ </para>
+ </sect2>
+</sect1>
+
+<sect1 id='dependency-resolution-package-modeling-conflicts'>
+ <title>Conflicts</title>
+ <sect2 id='dependency-resolution-package-modeling-blocker-conflicts'>
+ <title>Blocker Conflicts</title>
+ <para>
+ If one package blocks another package, the two packages
+ conflict such that they cannot be installed simultaneously.
+ These conflicts are often due to file collisions.
+ </para>
+ </sect2>
+ <sect2 id='dependency-resolution-package-modeling-slot-conflicts'>
+ <title>Slot Conflicts</title>
+ <para>
+ If two different packages that occupy the same slot are chosen
+ to satisfy dependencies, a slot conflict occurs. The two packages
+ cannot be installed simultaneously and therefore the respective
+ dependencies will not be satisfied simultaneously.
+ </para>
+ </sect2>
+ <sect2 id='dependency-resolution-package-modeling-indirect-conflicts'>
+ <title>Indirect Conflicts</title>
+ <para>
+ If the dependencies of two parent packages cannot be installed
+ simultaneously, it creates an indirect conflict between the parent
+ packages since their respective dependencies cannot be satisfied
+ simultaneously.
+ </para>
+ </sect2>
+</sect1>
+
+<sect1 id='dependency-resolution-package-modeling-dependency-neglection'>
+ <title>Dependency Neglection</title>
+ <para>
+ In order to significantly reduce the resources consumed by
+ the modeling process, the dependencies of
+ installed packages may be neglected.
+ </para>
+ <para>
+ If a more complete dependency calculation is desired,
+ there is a --complete-graph option which will ensure that the
+ dependencies of installed packages are properly considered.
+ </para>
+</sect1>
+
+</chapter>
--- /dev/null
+<chapter id='dependency-resolution-task-scheduling'>
+<title>Task Scheduling</title>
+<sect1 id='dependency-resolution-task-scheduling-dependencies'>
+ <title>Task Dependencies</title>
+ <para>
+ All tasks are executed in an order such
+ that a task's dependencies are satisfied
+ when it is executed. Dependency relationships between tasks
+ form a directed graph.
+ </para>
+</sect1>
+<sect1 id='dependency-resolution-task-scheduling-conflict-avoidance'>
+ <title>Conflict Avoidance</title>
+ <para>
+ In some cases it is possible to adjust package installation order
+ to avoid having two conflicting packages installed simultaneously.
+ </para>
+ <para>
+ TODO: Automatically uninstall packages when necessary to avoid conflicts.
+ </para>
+</sect1>
+<sect1 id='dependency-resolution-task-scheduling-circular-dependencies'>
+ <title>Circular Dependencies</title>
+ <para>
+ TODO: Automatically solve circular dependencies by temporarily disabling
+ conditional dependencies and then rebuilding packages with the conditional
+ dependencies enabled.
+ </para>
+</sect1>
+<sect1 id='dependency-resolution-task-scheduling-parallel'>
+ <title>Parallel Scheduling</title>
+ <para>
+ TODO: Spawn an appropriate number of tasks in parallel when desired.
+ </para>
+</sect1>
+</chapter>
<!ENTITY project "portage">
+ <!ENTITY dependency_resolution SYSTEM "dependency_resolution.docbook">
+ <!ENTITY dependency_resolution_package_modeling SYSTEM "dependency_resolution/package_modeling.docbook">
+ <!ENTITY dependency_resolution_decision_making SYSTEM "dependency_resolution/decision_making.docbook">
+ <!ENTITY dependency_resolution_task_scheduling SYSTEM "dependency_resolution/task_scheduling.docbook">
<!ENTITY package SYSTEM "package.docbook">
<!ENTITY package_ebuild SYSTEM "package/ebuild.docbook">
<!ENTITY package_ebuild_phases SYSTEM "package/ebuild/phases.docbook">
</bookinfo>
&config;
+&dependency_resolution;
&package;
&qa;
projects / portage.git / commitdiff