X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?p=topbloke-formulae.git;a=blobdiff_plain;f=strategy.tex;h=6fb4b4f9d2b72837ccfc8b602c7696cb93c74fd6;hp=532b24e86ef0be422888ab8f51ea973c369f8bd7;hb=bb9635f169e0014d28a8ba992e5ab285b1ff16ea;hpb=e6e07a7cef3baaf2751438efa0b70828ef1b1da5 diff --git a/strategy.tex b/strategy.tex index 532b24e..6fb4b4f 100644 --- a/strategy.tex +++ b/strategy.tex @@ -1,9 +1,27 @@ -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 $\patchof{L}$. - -\stdsection{Notation} +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. + +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. + +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} @@ -14,7 +32,7 @@ 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 contributors the +The Topbloke commit set $\pc$ has as a direct contributor the commit set $\p$. This is an acyclic relation. \item[ $\p \hasdep \pq$ ] @@ -23,22 +41,86 @@ set $\pq$. 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[ $ \grefzc, \grefcc, \grefuc, \greffc $ ] -The git ref for the Topbloke commit set $\pc$: respectively, -the original, current, updated, and final values. +%\item[ $ \tipzc, \tipcc, \tipuc, \tipfc $ ] +%The git ref for the Topbloke commit set $\pc$: respectively, +%the original, current, updated, and final values. \end{basedescript} +\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 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 + \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 planning phase computes: +The results of the planning phase consist of: \begin{itemize*} -\item{ The relation $\hasdirdep$ and hence the ordering $\hasdep$. } -\item{ For each commit set $\pc$, the order in which to merge +\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*} @@ -49,7 +131,7 @@ 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 $\grefzc$, to make $\greffc$. +into $\tipzc$, to make $\tipfc$. We start with $\pc = \pl$ where $\pl = \patchof{L}$. @@ -67,7 +149,7 @@ 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 $\set D_0 = \depsreqof{\grefzc}$. +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 @@ -96,34 +178,86 @@ $\pqn$ 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 $\greffc$ from -$\grefzc$, as planned. By construction, $\hasdep$ has $\patchof{L}$ +$\hasdep$. 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 -$\greffa{\patchof{L}}$. +$\tipca{\patchof{L}}$ with $\tipfa{\patchof{L}}$. -After we are done, the result has the following properties: -\[ \eqn{Best Tip}{ - \bigforall_{E_i \in \set E_{\pc}} \greffc \ge E_i +After we are done with each commit set $\pc$, the +new tip $\tipfc$ has the following properties: +\[ \eqn{Tip Sources}{ + \bigforall_{E_i \in \set E_{\pc}} \tipfc \ge E_i +}\] +\[ \eqn{Tip Dependencies}{ + \bigforall_{\pc \hasdep \p} \tipfc \ge \tipfa \p }\] \[ \eqn{Perfect Contents}{ - \greffc \haspatch \p \equiv \pc \hasdep \py + \tipfc \haspatch \p \equiv \pc \hasdep \py }\] -For brevity we will write $\grefu$ for $\grefuc$, etc. We will start -out with $\grefc = \grefz$, and at each step of the way construct some -$\grefu$ from $\grefc$. The final $\grefu$ becomes $\greff$. +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 $\ge \grefc$. If +Firstly, we will check each $E_i$ for being $\ge \tipc$. If it is, are we fast forward to $E_i$ ---- formally, $\grefu = \text{max}(\grefc, E_i)$ --- +--- formally, $\tipu = \text{max}(\tipc, E_i)$ --- and drop $E_i$ from the planned ordering. -\subsection{Merge Contributors for UP TO HERE} +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.~~$\qed$ + +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 $\py$ + with $M=M_j, L=T_{\pc,j-1}, R=E_j$, and calculate what the resulting desired direct dependencies file