X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=topbloke-formulae.git;a=blobdiff_plain;f=strategy.tex;h=27c9fd82b98d79868af1d126318e16004d42c2ae;hp=d9a2545f1db52b98ed9d8330cd1dfd55e91c561f;hb=HEAD;hpb=f0f7eceb4c3b65e4728d0b04b23e28906d5038fb

diff --git a/strategy.tex b/strategy.tex
index d9a2545..27c9fd8 100644
--- a/strategy.tex
+++ b/strategy.tex
@@ -6,7 +6,7 @@ remove dependencies from patches.
 
 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
+(and incidentally 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
@@ -32,24 +32,41 @@ The set of direct dependencies (in the form $\py$)
 requested in the commit $K$ ($K \in \pn$) for the patch $\p$.
 
 \item[ $\pc \hasdirdep \p$ ]
-The Topbloke commit set $\pc$ has as a direct contributor the
-commit set $\p$.  This is an acyclic relation.
+The patch $\pc$ has as a direct dependency the
+patch $\p$.  This is an acyclic relation.
 
 \item[ $\p \hasdep \pq$ ]
-The commit set $\p$ has as direct or indirect contributor the commit
-set $\pq$.
+The patch $\p$ has as direct or indirect dependency the
+patch $\pq$.
 Acyclic; the completion of $\hasdirdep$ into a
 partial order.
 
 \item[ $\pendsof{\set J}{\p}$ ]
 Convenience notation for
-the maximal elements of $\bigcup_{J \in \set J} \pendsof{J}{\p}$
+the $\le$-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[ $\allsrcs$ ]
+$\bigcup_{\p \in \allpatches} \set H^{\pn} \cup \set H^{\py}$.
+All the input commits to the update algorithm.  (See below.)
+
+\item[ $\set H^{\pc^{_=/-}}$ ]
+
+The existing head commit(s) $\set H$ of the branch $\pc^{+/-}$.
+These are the heads which will be merged and used in this update.
+This will include the current local and remote git refs, as desired.
+Obtained from the function $h$ (see below).
+
+\item[ $W$ ]
+
+During the Traversal phase, when we generate new commits, the working
+head of the branch we are working on.  Starts at $W_0$, updated as the
+algorithm progresses, and ultimately used to set $T$.
+
 %\item[ $\set E_{\pc}$ ]
 %$ \bigcup_i \pendsof{S_{\pc,i}}{\pc} $.
 %All the ends of $\pc$ in the sources.
@@ -70,9 +87,14 @@ $\bigforall_{E \in \pendsof{\set X}{\p}} E \le T$
 The topmost patch which we are trying to update.  This and
 all of its dependencies will be updated.
 
-\item[ $h : \pc^{+/-} \mapsto \set H_{\pc^{+/-}}$ ]
+\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[ $w : \pc^{+/-} \mapsto W_0^{\pc^{+/-}}$ ]
+
+Function for getting the existing local head of the branch
+$\pc^{+/-}$.  I.e., the current value of the branch ref for $\pc^{+/-}$.
+$W_0^{\pc^{+/-}} \in \set H$.
 
 \item[ $g : \pc, \Gamma \mapsto \Gamma'$ ]
 Function to allow explicit adjustment of the direct dependencies
@@ -80,262 +102,43 @@ 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 $\hasdirdep$.
+(acyclic) relations $\hasdirdep$ and $\hasdep$.
 
 \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 no edges.
-\item Execute {\bf Rank-Recurse}($\pc_0$)
-\item Until $\allpatches$ remains unchanged.
-\end{enumerate}
-\end{enumerate}
-
-{\bf Rank-Recurse}($\pc$) is:
-\begin{enumerate}
-
-\item If we have already done {\bf Rank-Recurse}($\pc$) in this
-ranking iteration, do nothing.  Otherwise:
-
-\item Add $\pc$ to $\allpatches$ if it is not there already.
-
-\item Let
-$$
-  \set S = h(\pcn)
-     \cup 
-        \bigcup_{\p \in \allpatches}
-        \bigcup_{H \in h(\pn) \lor H \in h(\py)}
-         \{ \baseof{E} \; | \; E \in \pendsof{H}{\pcy} \}
-$$
-
-and $W = w(h(\pcn))$
-
-\item While $\exists_{S \in \set S} S \ge W$,
-update $W \assign S$ and $\set S \assign \set S \, \backslash \{ S \}$
-
-(This will often remove $W$ from $\set S$.  Afterwards, $\set S$
-is a collection of heads to be merged into $W$.)
-
-\item Choose an order of $\set S$, $S_i$ for $i=1 \ldots n$.
-
-\item For each $S_i$ in turn, choose a corresponding $M_i$
-such that $$
-   M_i \le S_i \land \left[
-   M_i \le W \lor \bigexists_{S_i, j<i} M_i \le s_i
-   \right]
-$$
-
-\item Set $\Gamma = \depsreqof{W}$.
-
-If there are multiple candidates we prefer $M_i \in \pcn$
-if available.
-
-\item For each $i \ldots 1..n$, update our putative direct
-dependencies:
-$$
-\Gamma \assign \text{\bf set-merge}\left(\Gamma, 
- \left[ \begin{cases} 
-  M_i \in \pcn :     & \depsreqof{M_i} \\
-  M_i \not\in \pcn : & \{ \}
- \end{cases} \right],
- \depsreqof{S_i}
- \right)
-$$
-
-\item Finalise our putative direct dependencies
-$
-\Gamma \assign g(\pc, \Gamma)
-$
-
-\item For each direct dependency $\pd \in \Gamma$,
-
-\begin{enumerate}
-\item Add an edge $\pc \hasdirdep \pd$ to the digraph (adding nodes
-as necessary).
-If this results in a cycle, abort entirely (as the function $g$ is
-inappropriate; a different $g$ could work.)
-\end{enumerate}
-\item Run ${\text{\bf Rank-Recurse}}(\pd)$.
-
-\end{enumerate}
-
-The results of the ranking phase are:
-
-$ \allpatches, \hasdirdep $ and hence the completion of $\hasdirdep$
-into the partial order $\hasdep$.
-
-For each $\pc$, the base branch starting point commit $W_{\pcn} = W$,
-the direct dependencies $\Gamma_{\pc}$,
-the ordered set of base branch sources $\set S_{\pcn} = \set S,
-S_{\pcn,i} = S_i$
-and corresponding merge bases $M_{\pcn,i} = M_i$.
-
+\stdsection{Important variables and values in the update algorithm}
 
-
-\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 $\pc$.
-At each recursive step 
-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 $\tipzc$, to make $\tipfc$.
-
-We start with $\pc = \pl$ where $\pl = \patchof{L}$.
-
-
-\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 $\set E_{\pc}$, $E_{\pc,j}$
-($j = 1 \ldots m$).
-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 $\set D_0 = \depsreqof{\tipzc}$.
-For each $E_j$ starting with $j=1$ choose a corresponding intended
-merge base $M_j$ such that $M_j \le E_j \land M_j \le T_{\pc,j-1}$.
-Calculate $\set D_j$ as the 3-way merge of the sets $\set D_{j-1}$ and
-$\depsreqof{E_j}$ using as a base $\depsreqof{M_j}$.  This will
-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
+\begin{basedescript}{
+\desclabelwidth{5em}
+\desclabelstyle{\nextlinelabel}
 }
+\item[ $\Gamma_{\pc}$ ]
+The desired direct dependencies of $\pc$, a set of patches.
 
-\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.~~$\qed$
+\item[ $\allpatches$ ]
+The set of all the patches we are dealing with (constructed
+during the update algorithm).
 
-WIP UP TO HERE
+\item[ $\tipcn, \tipcy$ ]
+The new tips of the git branches $\pcn$ and $\pcy$, containing
+all the appropriate commits (and the appropriate other patches),
+as generated by the Traversal phase of the update algorithm.
 
-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 $
+\item[ $\allreach$ ]
+The set of all reachable commits.
 
-want to prove $E \le \tipfc$ where $E \in \pendsof{\tipcc}{\py}$
+A reachable commit is one we might refer to explicitly in any of these
+algorithms, and any ancestor of such a commit.  We explicitly
+enumerate all of the input commits ($\allsrcs$), so the reachable
+commits are originally the input commits and their ancestors.
 
-$\pancsof{\tipcc}{\py} = $
+$\allreach$ varies over time as we generate more commits.  Each
+commit we generate will have only reachable commits as ancestors, so
+generating a new commit (only) adds that new commit to $\allreach$.
 
+\item[ $\allreachof{\pn}$, $\allreachof{\py}$ ]
+The sets of reachable commits at the point where we have just generated
+$\tippn$ or $\tippy$, i.e. just after $\alg{Merge-Base}(\p)$ or
+$\alg{Recreate-Base}(\p)$, or $\alg{Merge-Tip}(\p)$, respectively.
 
-computed $\tipfa \py$, and by Perfect Contents for $\py$
-
-
-with $M=M_j, L=T_{\pc,j-1}, R=E_j$,
-and calculate what the resulting desired direct dependencies file
-(ie, the set of patches $\set D_j$)
-would be.  Eventually we 
-
-So, formally, we select somehow an order of sources $S_i$.  For each 
-
-
-Make use of the following recursive algorithm, Plan 
-
-
-
-
- recursively make a plan to merge all $E = \pends$
-
-Specifically, in
+\end{basedescript}