XGitUrl: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=topblokeformulae.git;a=blobdiff_plain;f=strategy.tex;h=6fb4b4f9d2b72837ccfc8b602c7696cb93c74fd6;hp=50efed7c8598cbf61a0e9b349b9dece2e3634267;hb=bb9635f169e0014d28a8ba992e5ab285b1ff16ea;hpb=d38e61b9455e0d0d4e9faadf5df29bb75a125331
diff git a/strategy.tex b/strategy.tex
index 50efed7..6fb4b4f 100644
 a/strategy.tex
+++ b/strategy.tex
@@ 1,11 +1,27 @@
\section{Strategy}
+Here we describe the update algorithm. This is responsible for
+refreshing patches against updated versions of their dependencies,
+for merging different versions of the various braches created by
+distributed development, and for implementing decisions to add and
+remove dependencies from patches.
When we are trying to do a merge of some kind, in general,
we want to merge some source commits $S_0 \ldots S_n$.
We'll write $S_0 = L$. We require that $L$ is the current git ref
for $\patchof{L}$.
+Broadly speaking the update proceeds as follows: during the Ranking
+phase we construct the intended graph of dependencies between patches
+(which involves select a merge order for the base branch of each
+patch). Then during the Traversal phase we walk that graph from the
+bottom up, constructing for each patch by a series of merges and other
+operations first a new base branch head commit and then a new tip
+branch head commit. These new head commits are maximums  that is,
+each has as ancestors all of its branches' sources and indeed all
+relevant commits in that branch.
\subsection{Notation}
+We have two possible strategies for constructing new base branch
+heads: we can either Merge (works incrementally even if there the
+patch has multiple dependencies, but may sometimes not be possible) or
+we can Regenerate (trivial if there is a single dependency, and is
+always possible, but may involve the user reresolving conflicts if
+there are multiple dependencies).
+
+\section{Notation}
\begin{basedescript}{
\desclabelwidth{5em}
@@ 15,63 +31,233 @@ for $\patchof{L}$.
The set of direct dependencies (in the form $\py$)
requested in the commit $K$ ($K \in \pn$) for the patch $\p$.
\item[ $\pc \succ_1 \{ \p, \pq \ldots \}$ ]
The Topbloke commit set $\pc$ has as direct contributors
(see below) exactly $\p, \pq, \ldots$. This is an acyclic relation.
+\item[ $\pc \hasdirdep \p$ ]
+The Topbloke commit set $\pc$ has as a direct contributor the
+commit set $\p$. This is an acyclic relation.
\item[ $\p \succ \pq$ ]
+\item[ $\p \hasdep \pq$ ]
The commit set $\p$ has as direct or indirect contributor the commit
set $\pq$.
This is an acyclic relation, and is the completion of $\succ_1$ into a
+Acyclic; the completion of $\hasdirdep$ into a
partial order.
\item[ $\set E_{\pc}$ ]
$ \bigcup_i \pendsof{S_i}{\pc} $.
All the ends of $\pc$ in the sources.
+\item[ $\pendsof{\set J}{\p}$ ]
+Convenience notation for
+the maximal elements of $\bigcup_{J \in \set J} \pendsof{J}{\p}$
+(where $\set J$ is some set of commits).
+
+\item[ $\pendsof{\set X}{\p} \le T$ ]
+Convenience notation for
+$\bigforall_{E \in \pendsof{\set X}{\p}} E \le T$
+
+%\item[ $\set E_{\pc}$ ]
+%$ \bigcup_i \pendsof{S_{\pc,i}}{\pc} $.
+%All the ends of $\pc$ in the sources.
+
+%\item[ $ \tipzc, \tipcc, \tipuc, \tipfc $ ]
+%The git ref for the Topbloke commit set $\pc$: respectively,
+%the original, current, updated, and final values.
\end{basedescript}
\subsection{Planning phase}
+\stdsection{Inputs to the update algorithm}
+
+\begin{basedescript}{
+\desclabelwidth{5em}
+\desclabelstyle{\nextlinelabel}
+}
+\item[ $\pc_0$ ]
+The topmost patch which we are trying to update. This and
+all of its dependencies will be updated.
+
+\item[ $h : \pc^{+/} \mapsto \set H_{\pc^{+/}}$ ]
+Function for getting the existing heads $\set H$ of the branch $\pc^{+/}$.
+This will include the current local and remote git refs, as desired.
+
+\item[ $g : \pc, \Gamma \mapsto \Gamma'$ ]
+Function to allow explicit adjustment of the direct dependencies
+of $\pc$. It is provided with a putative set of direct dependencies
+$\Gamma$ computed as an appropriate merge of the dependencies requested by the
+sources and should return the complete actual set $\Gamma'$ of direct
+dependencies to use. This allows the specification of any desired
+(acyclic) relation $\hasdirdep$.
+
+\end{basedescript}
+
+\section{Ranking phase}
+
+We run the following algorithm:
+\begin{enumerate}
+\item Set $\allpatches = \{ \}$.
+\item Repeatedly:
+\begin{enumerate}
+\item Clear out the graph $\hasdirdep$ so it has neither nodes nor edges.
+\item Execute {\bf RankRecurse}($\pc_0$)
+\item Until $\allpatches$ remains unchanged.
+\end{enumerate}
+\end{enumerate}
+
+{\bf RankRecurse}($\pc$) is:
+\begin{enumerate}
+\item Add $\pc$ to $\allpatches$ if it is not there already.
+\item Let $\set S_{\pcn} = h(\pcn)
+ \cup
+ \bigcup_{\p \in \allpatches}
+ \bigcup_{H \in h(\pn) \lor H \in h(\py)}
+ \{ \baseof{E} \;  \; E \in \pendsof{H}{\pcy} \} $
+
+and $W = w(h(\pcn))$
+
+We write $\set S = \set S_{\pcn}$ where unambiguous.
+\item While $\exists_{S \in \set S} S \ge W$:
+
+Update $W \assign S$ and $\set S \assign \set S \, \backslash \{ S \}$
+\end{enumerate}
+
+\section{Planning phase}
+
+The results of the planning phase consist of:
+\begin{itemize*}
+\item{ The relation $\hasdirdep$ and hence the partial order $\hasdep$. }
+\item{ For each commit set $\pc$, a confirmed set of sources $\set S_{\pc}$. }
+\item{ For each commit set $\pc$, the order in which to merge the sources
+ $E_{\pc,j} \in \set E_{\pc}$. }
+\item{ For each $E_{\pc,j}$ an intended merge base $M_{\pc,j}$. }
+\end{itemize*}
We use a recursive planning algorith, recursing over Topbloke commit
sets (ie, sets $\py$ or $\pn$). We'll call the commit set we're
processing at each step $\pc$. We start with $\pc = \pl$
where $\pl = \patchof{L}$.

+processing at each step $\pc$.
At each recursive step
we intend to merge all $\set E_{\pc} = \{ E_{\pc,j \ldots} \}$
+we make a plan to merge all $\set E_{\pc} = \{ E_{\pc,j \ldots} \}$
and all the direct contributors of $\pc$ (as determined below)
into the existing git ref for $\pc$, to make $T_{\pc}$.
The direct contributors of $\pcn$ are the Topbloke commit sets
corresponding to the tip branches for the direct dependencies of
$\pc$.
The sole direct contributor of $\pcy$ is $\pcn$.
+into $\tipzc$, to make $\tipfc$.
+
+We start with $\pc = \pl$ where $\pl = \patchof{L}$.
+
\subsubsection{Planning step for $\pc = \pcn$.}
+\subsection{Direct contributors for $\pc = \pcn$}
+
+The direct contributors of $\pcn$ are the commit sets corresponding to
+the tip branches for the direct dependencies of the patch $\pc$. We
+need to calculate what the direct dependencies are going to be.
Choose an (arbitrary, but ideally somehow optimal in
a way not discussed here) ordering of $\set E_{\pc}$, $E_j$ (for
$j = 1 \ldots m$). Remove from that set (and ordering) any $E_j$ which
+a way not discussed here) ordering of $\set E_{\pc}$, $E_{\pc,j}$
+($j = 1 \ldots m$).
+For brevity we will write $E_j$ for $E_{\pc,j}$.
+Remove from that set (and ordering) any $E_j$ which
are $\le$ and $\neq$ some other $E_k$.
Initially let $T_{\pc,0}$ be the git ref for $\pcn$. And let
$\set D_0 = \depsreqof{T_{\pc,0}}$.
+Initially let $\set D_0 = \depsreqof{\tipzc}$.
For each $E_j$ starting with $j=1$ choose a corresponding intended
merge base $M_j$ such that $M_j \le E_j \land M_j \le T_{\pc,j1}$.
Calculate $\set D_j$ as the 3way merge of the sets $\set D_{j1}$ and
$\depsreqof{E_j}$ using as a base $\depsreqof{M_j}$. This will
generate $D_m$ as the putative direct contributors for $\pcn$.
+generate $D_m$ as the putative direct contributors of $\pcn$.
+
+However, the invocation may give instructions that certain direct
+dependencies are definitely to be included, or excluded. As a result
+the set of actual direct contributors is some arbitrary set of patches
+(strictly, some arbitrary set of Topbloke tip commit sets).
+
+\subsection{Direct contributors for $\pc = \pcy$}
+
+The sole direct contributor of $\pcy$ is $\pcn$.
+
+\subsection{Recursive step}
+
+For each direct contributor $\p$, we add the edge $\pc \hasdirdep \p$
+and augment the ordering $\hasdep$ accordingly.
+
+If this would make a cycle in $\hasdep$, we abort . The operation must
+then be retried by the user, if desired, but with different or
+additional instructions for modifying the direct contributors of some
+$\pqn$ involved in the cycle.
+
+For each such $\p$, after updating $\hasdep$, we recursively make a plan
+for $\pc' = \p$.
+
+
+
+\section{Execution phase}
+
+We process commit sets from the bottom up according to the relation
+$\hasdep$. For each commit set $\pc$ we construct $\tipfc$ from
+$\tipzc$, as planned. By construction, $\hasdep$ has $\patchof{L}$
+as its maximum, so this operation will finish by updating
+$\tipca{\patchof{L}}$ with $\tipfa{\patchof{L}}$.
+
+After we are done with each commit set $\pc$, the
+new tip $\tipfc$ has the following properties:
+\[ \eqn{Tip Sources}{
+ \bigforall_{E_i \in \set E_{\pc}} \tipfc \ge E_i
+}\]
+\[ \eqn{Tip Dependencies}{
+ \bigforall_{\pc \hasdep \p} \tipfc \ge \tipfa \p
+}\]
+\[ \eqn{Perfect Contents}{
+ \tipfc \haspatch \p \equiv \pc \hasdep \py
+}\]
+
+For brevity we will sometimes write $\tipu$ for $\tipuc$, etc. We will start
+out with $\tipc = \tipz$, and at each step of the way construct some
+$\tipu$ from $\tipc$. The final $\tipu$ becomes $\tipf$.
+
+\subsection{Preparation}
+
+Firstly, we will check each $E_i$ for being $\ge \tipc$. If
+it is, are we fast forward to $E_i$
+ formally, $\tipu = \text{max}(\tipc, E_i)$ 
+and drop $E_i$ from the planned ordering.
+
+Then we will merge the direct contributors and the sources' ends.
+This generates more commits $\tipuc \in \pc$, but none in any other
+commit set. We maintain
+$$
+ \bigforall_{\p \isdep \pc}
+ \pancsof{\tipcc}{\p} \subset
+ \pancsof{\tipfa \p}{\p}
+$$
+\proof{
+ For $\tipcc = \tipzc$, $T$ ...WRONG WE NEED $\tipfa \p$ TO BE IN $\set E$ SOMEHOW
+}
+
+\subsection{Merge Contributors for $\pcy$}
+
+Merge $\pcn$ into $\tipc$. That is, merge with
+$L = \tipc, R = \tipfa{\pcn}, M = \baseof{\tipc}$.
+to construct $\tipu$.
+
+Merge conditions:
+
+Ingredients satisfied by construction.
+Tip Merge satisfied by construction. Merge Acyclic follows
+from Perfect Contents and $\hasdep$ being acyclic.
+
+Removal Merge Ends: For $\p = \pc$, $M \nothaspatch \p$; OK.
+For $\p \neq \pc$, by Tip Contents,
+$M \haspatch \p \equiv L \haspatch \p$, so we need only
+worry about $X = R, Y = L$; ie $L \haspatch \p$,
+$M = \baseof{L} \haspatch \p$.
+By Tip Contents for $L$, $D \le L \equiv D \le M$. OK.~~$\qed$
However, the invocation may specify that certain direct dependencies
are definitely to be included, or excluded. As a result the set
of actual direct contributors is some arbitrary set of patches.
+WIP UP TO HERE
+Addition Merge Ends: If $\py \isdep \pcn$, we have already
+done the execution phase for $\pcn$ and $\py$. By
+Perfect Contents for $\pcn$, $\tipfa \pcn \haspatch \p$ i.e.
+$R \haspatch \p$. So we only need to worry about $Y = R = \tipfa \pcn$.
+By Tip Dependencies $\tipfa \pcn \ge \tipfa \py$.
+And by Tip Sources $\tipfa \py \ge $
+want to prove $E \le \tipfc$ where $E \in \pendsof{\tipcc}{\py}$
+$\pancsof{\tipcc}{\py} = $
+computed $\tipfa \py$, and by Perfect Contents for $\py$
Imagine that we will merge the direct
with $M=M_j, L=T_{\pc,j1}, R=E_j$,
and calculate what the resulting desired direct dependencies file