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Overview

Comment: | Updated commentary regarding cycles at this point, items instead of comments, etc. |
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Downloads: | Tarball | ZIP archive | SQL archive |

Timelines: | family | ancestors | descendants | both | trunk |

Files: | files | file ages | folders |

SHA1: | af5904e6b7fade5c921695af0088a8c1 |

User & Date: | aku 2007-11-29 09:14:51 |

Context

2007-11-29
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09:15 | Fix bad variable name. check-in: 48593049 user: aku tags: trunk | |

09:14 | Updated commentary regarding cycles at this point, items instead of comments, etc. check-in: af5904e6 user: aku tags: trunk | |

09:13 | Extended checks for looped changesets. check-in: 96064544 user: aku tags: trunk | |

Changes

Changes to tools/cvs2fossil/lib/c2f_pbreakacycle.tcl.

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# created by the symbols which are translated as branches, and # break any which are 'backward', which means that they have # at least one incoming revision changeset which is committed # after at least one of the outgoing revision changesets, per # the order computed in pass 6. In "cvs2svn" this is called # "retrograde". # NOTE: We might be able to use our knowledge that we are # looking at all changesets to create a sql which selects all # the branch changesets from the state in one go instead of # having to check each changeset separately. Consider this # later, get the pass working first. # # NOTE 2: Might we even be able to select the backward branch # changesets too ? foreach cset [$graph nodes] { if {![$cset bysymbol]} continue CheckAndBreakBackward $graph $cset } return } proc CheckAndBreakBackward {graph cset} { while {[IsBackward $graph $cset]} { # Knowing that the branch is backward we now look at the # individual revisions in the changeset and determine # which of them are responsible for the overlap. This # allows us to split them into two sets, one of # non-overlapping revisions, and of overlapping ones. Each # induces a new changeset, and the second may still be # backward and need further splitting. Hence the looping. # # The border used for the split is the minimal commit # position among the minimal sucessor commit positions for # the revisions in the changeset. # Note that individual revisions may not have revision # changesets are predecessors and/or successors, leaving # the limits partially or completely undefined. # limits : dict (revision -> list (max predecessor commit, min sucessor commit)) ComputeLimits $cset limits border log write 5 breakacycle "Breaking backward changeset [$cset str] with commit position $border as border" # Then we sort the file level items based on there they # sit relative to the border into before and after the # border. SplitRevisions $limits $border normalrevisions backwardrevisions set replacements [project::rev split $cset $normalrevisions $backwardrevisions] cyclebreaker replace $graph $cset $replacements # At last check that the normal frament is indeed not # backward, and iterate over the possibly still backward # second fragment. struct::list assign $replacements normal backward ................................................................................ } return } proc IsBackward {dg cset} { # A branch is "backward" if it has at least one incoming # revision changeset which is committed after at least one of # the outgoing revision changesets, per the order computed in # pass 6. # Rephrased, the maximal commit position found among the # incoming revision changesets is larger than the minimal # commit position found among the outgoing revision # changesets. Assuming that we have both incoming and outgoing # revision changesets. # The helper "Positions" computes the set of commit positions # for a set of changesets, which can be a mix of revision and # symbol changesets. set predecessors [Positions [$dg nodes -in $cset]] set successors [Positions [$dg nodes -out $cset]] ................................................................................ proc ToPosition {cset} { $cset pos } proc ValidPosition {pos} { expr {$pos ne ""} } proc ComputeLimits {cset lv bv} { upvar 1 $lv thelimits $bv border # Initialize the boundaries for all revisions. array set limits {} foreach revision [$cset revisions] { set limits($revision) {0 {}} } # Compute and store the maximal predecessors per revision foreach {revision csets} [$cset predecessormap] { set s [Positions $csets] if {![llength $s]} continue set limits($revision) [lreplace $limits($revision) 0 0 [max $s]] } # Compute and store the minimal successors per revision foreach {revision csets} [$cset successormap] { set s [Positions $csets] if {![llength $s]} continue set limits($revision) [lreplace $limits($revision) 1 1 [min $s]] } # Check that the ordering at the file level is correct. We # cannot have backward ordering per revision, or something is # wrong. foreach revision [array names limits] { struct::list assign $limits($revision) maxp mins # Handle min successor position "" as representing infinity integrity assert { ($mins eq "") || ($maxp < $mins) } {Branch revision $revision is backward at file level ($maxp >= $mins)} } # Save the limits for the splitter, and compute the border at # which to split as the minimum of all minimal successor # positions. set thelimits [array get limits] ................................................................................ set res {} foreach {k v} $dict { lappend res $v } return $res } proc MinSuccessorPosition {item} { lindex $item 1 } proc SplitRevisions {limits border nv bv} { upvar 1 $nv normalrevisions $bv backwardrevisions set normalrevisions {} set backwardrevisions {} foreach {rev v} $limits { struct::list assign $v maxp mins if {$maxp >= $border} { lappend backwardrevisions $rev } else { lappend normalrevisions $rev } } integrity assert {[llength $normalrevisions]} {Set of normal revisions is empty} integrity assert {[llength $backwardrevisions]} {Set of backward revisions is empty} return } # # ## ### ##### ######## ############# proc KeepOrder {graph at cset} { ................................................................................ if {[$cset pos] eq ""} return # For the revision changesets we are sure that they are # consumed in the same order as generated by pass 7 # (RevTopologicalSort). Per the code in cvs2svn. # IMHO this will work if and only if none of the symbol # changesets are "backwards", which explains the breaking of # the backward changesets first, in the pre-hook. A difference # to cvs2svn however is that we are breaking all backward # symbol changesets, both branch and tag. cvs2svn can # apparently assume here that tag symbol changesets are not # backwards, ever. We can't, apparently. It is unclear to me # where the difference is. # An interesting thing IMHO, is that after breaking backward # symbol changesets we should not have any circles any # longer. Each circle which was still present had to involve a # backward symbol, and that we split. # Proof: Let us assume we that have a circle # C: R1 -> ... -> Rx -> S -> Ry -> ... -> Rn -> R1 # Let us further assume that S is not backward. That means # ORD(Rx) < ORD(Ry). The earlier topological sorting without # symbols now forces this relationship through to be # ORD(Rx) < ORD(R1) < ORD(Rx). # We have reached an impossibility, a paradox. Our initial # assumption of S not being backward cannot hold. # # Alternate, direct, reasoning: Without S the chain of # dependencies is Ry -> .. -> R1 -> .. -> Rx, therefore # ORD(Ry) < ORD(Rx) holds, and this means S is backward. # NOTE. Even with the backward symbols broken, it is not clear # to me yet what this means in terms of tagging revisions # later, as we now have more than one place where the symbol # occurs on the relevant LOD. struct::set exclude myrevisionchangesets $cset ::variable mylastpos set new [$cset pos] if {$new != ($mylastpos + 1)} { if {$mylastpos < 0} { |
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# created by the symbols which are translated as branches, and # break any which are 'backward', which means that they have # at least one incoming revision changeset which is committed # after at least one of the outgoing revision changesets, per # the order computed in pass 6. In "cvs2svn" this is called # "retrograde". foreach cset [$graph nodes] { if {![$cset isbranch]} continue CheckAndBreakBackward $graph $cset } return } proc CheckAndBreakBackward {graph cset} { while {[IsBackward $graph $cset]} { # Knowing that the branch changeset is backward we now # look at the individual branches in the changeset and # determine which of them are responsible for the # overlap. This allows us to split them into two sets, one # of non-overlapping branches, and of overlapping # ones. Each set induces a new changeset, and the second # one may still be backward and in need of further # splitting. Hence the looping. # # The border used for the split is the minimal commit # position among the minimal sucessor commit positions for # the branches in the changeset. # Note that individual branches may not have changesets # which are their predecessors and/or successors, leaving # the limits partially or completely undefined. # limits : dict (revision -> list (max predecessor commit, min sucessor commit)) ComputeLimits $cset limits border log write 5 breakacycle "Breaking backward changeset [$cset str] with commit position $border as border" # Secondly we sort the file level items based on there # they sit relative to the border into before and after # the border. SplitItems $limits $border normalitems backwarditems set replacements [project::rev split $cset $normalitems $backwarditems] cyclebreaker replace $graph $cset $replacements # At last check that the normal frament is indeed not # backward, and iterate over the possibly still backward # second fragment. struct::list assign $replacements normal backward ................................................................................ } return } proc IsBackward {dg cset} { # A branch is "backward" if it has at least one incoming # revision changeset which is committed after at least one of # the outgoing revision changesets, per the order computed by # pass 6. # Rephrased, the maximal commit position found among the # incoming revision changesets is larger than the minimal # commit position found among the outgoing revision # changesets. Assuming that we have both incoming and outgoing # revision changesets for the branch. # The helper "Positions" computes the set of commit positions # for a set of changesets, which can be a mix of revision and # symbol changesets. set predecessors [Positions [$dg nodes -in $cset]] set successors [Positions [$dg nodes -out $cset]] ................................................................................ proc ToPosition {cset} { $cset pos } proc ValidPosition {pos} { expr {$pos ne ""} } proc ComputeLimits {cset lv bv} { upvar 1 $lv thelimits $bv border # Initialize the boundaries for all items. array set limits {} foreach revision [$cset items] { set limits($revision) {0 {}} } # Compute and store the maximal predecessors per item (branch) foreach {item csets} [$cset predecessormap] { set s [Positions $csets] if {![llength $s]} continue set limits($item) [lreplace $limits($item) 0 0 [max $s]] } # Compute and store the minimal successors per item (branch) foreach {item csets} [$cset successormap] { set s [Positions $csets] if {![llength $s]} continue set limits($item) [lreplace $limits($item) 1 1 [min $s]] } # Check that the ordering at the file level is correct. We # cannot have backward ordering per branch, or something is # wrong. foreach item [array names limits] { struct::list assign $limits($item) maxp mins # Handle min successor position "" as representing infinity integrity assert { ($mins eq "") || ($maxp < $mins) } {Item <$item> is backward at file level ($maxp >= $mins)} } # Save the limits for the splitter, and compute the border at # which to split as the minimum of all minimal successor # positions. set thelimits [array get limits] ................................................................................ set res {} foreach {k v} $dict { lappend res $v } return $res } proc MinSuccessorPosition {item} { lindex $item 1 } proc SplitItems {limits border nv bv} { upvar 1 $nv normalitems $bv backwarditems set normalitems {} set backwarditems {} foreach {rev v} $limits { struct::list assign $v maxp mins if {$maxp >= $border} { lappend backwarditems $rev } else { lappend normalitems $rev } } integrity assert {[llength $normalitems]} {Set of normal items is empty} integrity assert {[llength $backwarditems]} {Set of backward items is empty} return } # # ## ### ##### ######## ############# proc KeepOrder {graph at cset} { ................................................................................ if {[$cset pos] eq ""} return # For the revision changesets we are sure that they are # consumed in the same order as generated by pass 7 # (RevTopologicalSort). Per the code in cvs2svn. # This works if and only if none of the symbol changesets are # "backwards", hence our breaking of the backward changesets # first, in the pre-hook. # Note that tah changesets cannot be backward as they don't # have successors at all. # An interesting thing IMHO, is that after breaking the # backward symbol changesets we should not have any circles # any longer. Each circle which would still be present has to # involve a backward symbol, and we split them all, so there # can't be a circle.. # Proof: # Let us assume we that have a circle # C: R1 -> ... -> Rx -> S -> Ry -> ... -> Rn -> R1 # Let us further assume that the symbol changeset S in that # circle is not backward. That means ORD(Rx) < ORD(Ry). The # earlier topological sorting without symbols now forces this # relationship through to be ORD(Rx) < ORD(R1) < ORD(Rx). We # have reached an impossibility, a paradox. Our initial # assumption of S not being backward cannot hold. # # Alternate, direct, reasoning: Without S the chain of # dependencies is Ry -> .. -> R1 -> .. -> Rx, therefore # ORD(Ry) < ORD(Rx) holds, and this means S is backward. struct::set exclude myrevisionchangesets $cset ::variable mylastpos set new [$cset pos] if {$new != ($mylastpos + 1)} { if {$mylastpos < 0} { |