X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=topbloke-formulae.git;a=blobdiff_plain;f=strategy.tex;h=7b977e5870ea2a34256850fee8ab34eee2c2f54e;hp=50efed7c8598cbf61a0e9b349b9dece2e3634267;hb=cc6f8a852918817eecd961f9d2ce85b7ba13eb6f;hpb=d38e61b9455e0d0d4e9faadf5df29bb75a125331 diff --git a/strategy.tex b/strategy.tex index 50efed7..7b977e5 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 re-resolving conflicts if +there are multiple dependencies). + +\section{Notation} \begin{basedescript}{ \desclabelwidth{5em} @@ -15,63 +31,226 @@ 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} + +{\bf Ranking} is: +\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 Rank-Recurse}($\pc_0$) . +\item Until $\allpatches$ remains unchanged. +\end{enumerate} +\end{enumerate} + +{\bf Rank-Recurse}($\pc$) is: +\begin{enumerate} +\item Add $\pc$ to $\allpatches$ if it is not there already. +\item Let $\set S_{\pcn} = h(\pcn) + \cup \{ \baseof{E} \; | \; \pendsof{ \left[ + \bigcup_{\p \in \allpatches} h(\pn) \cup h(\py) + \right] + }{ \pcy } \} $ +\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 $\pl = \patchof{L}$. + + +\subsection{Direct contributors for $\pc = \pcn$} -\subsubsection{Planning step 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 $M_j \le E_j \land M_j \le T_{\pc,j-1}$. 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 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 $M=M_j, L=T_{\pc,j-1}, R=E_j$, and calculate what the resulting desired direct dependencies file