Introduce pkgDepCache::Transaction for transactional depcache updates

2 files changed, 109 insertions, 0 deletions

diff --git a/apt-pkg/depcache.cc b/apt-pkg/depcache.cc
index 970b4c01d..ec34d010b 100644
--- a/apt-pkg/depcache.cc
+++ b/apt-pkg/depcache.cc
@@ -2650,3 +2650,74 @@ unsigned long long pkgDepCache::BootSize(bool initrdOnly)
    return std::accumulate(sizes, sizes + MAX_ARTEFACT, off_t{0}) * BootCount * 110 / 100;
 }
 									/*}}}*/
+// pkgDepCache::Transaction						/*{{{*/
+struct pkgDepCache::Transaction::Private
+{
+   template <typename T>
+   static T *copyArray(T *array, size_t count)
+   {
+      auto out = new T[count];
+      memcpy(&out[0], &array[0], sizeof(T) * count);
+      return out;
+   }
+   // State information
+   pkgDepCache &cache;
+   Behavior behavior;
+   std::unique_ptr<StateCache[]> PkgState{copyArray(cache.PkgState, cache.GetCache().Head().PackageCount)};
+   std::unique_ptr<unsigned char[]> DepState{copyArray(cache.DepState, cache.GetCache().Head().DependsCount)};
+   signed long long iUsrSize{cache.iUsrSize};
+   unsigned long long iDownloadSize{cache.iDownloadSize};
+   unsigned long iInstCount{cache.iInstCount};
+   unsigned long iDelCount{cache.iDelCount};
+   unsigned long iKeepCount{cache.iKeepCount};
+   unsigned long iBrokenCount{cache.iBrokenCount};
+   unsigned long iPolicyBrokenCount{cache.iPolicyBrokenCount};
+   unsigned long iBadCount{cache.iBadCount};
+
+   void rollback()
+   {
+      memcpy(&cache.PkgState[0], &PkgState[0], sizeof(PkgState[0]) * cache.GetCache().Head().PackageCount);
+      memcpy(&cache.DepState[0], &DepState[0], sizeof(DepState[0]) * cache.GetCache().Head().DependsCount);
+
+      cache.iUsrSize = iUsrSize;
+      cache.iDownloadSize = iDownloadSize;
+      cache.iInstCount = iInstCount;
+      cache.iDelCount = iDelCount;
+      cache.iKeepCount = iKeepCount;
+      cache.iBrokenCount = iBrokenCount;
+      cache.iPolicyBrokenCount = iPolicyBrokenCount;
+      cache.iBadCount = iBadCount;
+   }
+};
+
+pkgDepCache::Transaction::Transaction(pkgDepCache &cache, Behavior behavior) : d(new Private{cache, behavior}) {}
+
+void pkgDepCache::Transaction::temporaryRollback()
+{
+   d->rollback();
+}
+
+void pkgDepCache::Transaction::commit()
+{
+   d.reset();
+}
+
+void pkgDepCache::Transaction::rollback()
+{
+   if (d == nullptr)
+      return;
+
+   temporaryRollback();
+   d.reset();
+}
+
+pkgDepCache::Transaction::~Transaction()
+{
+   if (not d)
+      return;
+   if (d->behavior == Behavior::ROLLBACK || (d->behavior == Behavior::AUTO && d->cache.iBrokenCount > d->iBrokenCount))
+      rollback();
+   else
+      commit();
+}
+									/*}}}*/
diff --git a/apt-pkg/depcache.h b/apt-pkg/depcache.h
index 39d34d3e4..d2a883180 100644
--- a/apt-pkg/depcache.h
+++ b/apt-pkg/depcache.h
@@ -267,6 +267,42 @@ class APT_PUBLIC pkgDepCache : protected pkgCache::Namespace
       bool InstallSuggests;
    };
 
+   /**
+    * \brief Perform changes to the depcache atomically.
+    *
+    * The default policy for a transaction is to rollback if the number of broken packages
+    * increased, otherwise to commit. Call commit() or rollback() to override the default
+    * policy.
+    */
+   class APT_PUBLIC Transaction final
+   {
+      struct Private;
+      std::unique_ptr<Private> d;
+
+      public:
+      enum class Behavior
+      {
+	 COMMIT,
+	 ROLLBACK,
+	 AUTO,
+      };
+
+      explicit Transaction(pkgDepCache &cache, Behavior behavior);
+      /** \brief Commit the transaction immediately */
+      void commit();
+      /** \brief Rollback the transaction immediately */
+      void rollback();
+      /** \brief Like rollback, but can be called multiple times.
+       *
+       * You can for example create a new transaction, then temporarily
+       * rollback to the state before the previous transaction in that
+       * transaction.
+       */
+      void temporaryRollback();
+      /** \brief Commit or rollback the transaction based on default policy */
+      ~Transaction();
+   };
+
    private:
    /** The number of open "action groups"; certain post-action
     *  operations are suppressed if this number is > 0.
@@ -274,6 +310,8 @@ class APT_PUBLIC pkgDepCache : protected pkgCache::Namespace
    int group_level;
 
    friend class ActionGroup;
+   friend class Transaction;
+
    public:
    int IncreaseActionGroupLevel();
    int DecreaseActionGroupLevel();